OSRAM OPTOTRONIC User Manual

www.osram.com/ledset

Application guide.

The LEDset interface.

CONTENTS

General notes:

As the specifi cations of the applied components are subject to change, OSRAM does not take

liability for the technical accuracy of the application solutions shown in this application guide.

For current specifi cations, please refer to the data sheets of the respective components.

Please also note that LED standards are changing rapidly and that this application guide can

therefore only refl ect the status of the listed standards on the date published. Please check the

latest edition of any standard at the following websites or with your national trade association.

www.cenelec.org

www.cen.eu

www.iec.ch

2

CONTENTS

1. Introduction 4

1.1. Features and benefi ts 5

2. LEDset specifi cations 6

2.1. General overview 6

2.2. LEDset characteristic 7

2.2.1. General description 7

2.2.2. Implementation in the OSRAM ECG 8

2.3. Technical details 9

2.3.1. Bias current (Iset) 9

2.3.2. +12Vset 9

2.3.3. Fault protection 9

2.3.4. Insulation 9

2.3.5. Color coding 10

2.3.6. Cable length 10

2.3.7. Fault conditions/troubleshooting 10

2.3.7.1. Incorrect wiring 10

2.3.7.2. Missing control wire (Vset) 10

2.3.8. Connection of multiple ECGs 11

3. LEDset applications 12

3.1. Current setting 12

3.1.1. Setting by external resistor 12

3.1.2. Step dimming (StepDIM) 15

3.2. Local dimming 17

3.2.1. Potentiometer application 17

3.2.2. Light sensor application 18

3.2.2.1. Using OSRAM DIM
MICO/PICO 18

3.2.2.2. Using customized sensors 19

3.2.2.3. General notes on local
dimming: LEDset, “current set”
combination 20

3.3. Thermal derating 22

3.3.1. Overtemperature protection 24

3.3.1.1. Application solution 1 –
TMP300 solution 24

3.3.1.2. Application solution 2 –
LM26 solution 26

3.3.1.3. Application solution 3 –
NPC SM6611 solution 27

3.3.1.4. Application solution 4 –
SI S-5841 solution 28

3.3.1.5. Application solution 5 –
MM3488 solution 29

3.3.1.6. Application solution 6 –
TC620(1) solution 30

3.3.1.7. General notes on IC
temperature switches:
choice and usage 33

3.3.2. Overtemperature protection

(discrete NTC) 34

3.3.2.1. Application solution 1 –
overtemperature protection
by comparator 34

3.3.2.2. Application solution 2 –
overtemperature management
by comparator:
two-step output 36

3.3.2.3. Application solution 3 –
overtemperature management:
continuous derating
and switch-off 38

3.3.2.4. Application solution 4 –

LEDset and current set
combination: direct NTC
connection 40

3.3.2.5. Application solution 5 –
overtemperature management:
microcontroller
(MCU) approach 42

3.4. +12Vset auxiliary supply 46

3.4.1. Aesthetic use 46

3.4.2. Active cooling 47

3.5. Constant lumen output 48

3.6. Combination of features 49

3

INTRODUCTION

1. Introduction

LED technology is changing the world of general lighting. In

luminaire design, however, the various benefi ts of LEDs, e.g.

their high level of fl exibility in operating luminaires, can only

be achieved with perfectly matched control gears. This is fur-

ther complicated by the rapid improvement of the effi cacy

and current capability of LED technologies, which asks for

even greater adaptability of the corresponding control gears.

Purpose of this application guide:

The purpose of this application guide is to provide basic techni-

cal information on the LEDset interface, focusing on application

solutions that illustrate the specifi c functions of this new inter-

face and show how these can be used. The application solutions

demonstrate that the LEDset interface opens up many opportu-

nities for customizing your LED-based luminaire: the simplicity

and fl exibility of LEDset gives you the freedom to develop new

luminaire system features.

OPTOTRONIC

this demand for greater adaptability by supporting a wide

power and current range and by their future-proof design,

which makes them ready for coming LED generations.

®

control gears with LEDset interface can meet

4

1.1. Features and benefi ts

INTRODUCTION

LEDset helps you to meet important market requirements:

• Future-proof solutions in terms of lumen output

• Long-life operation

• Customization of the luminaire

• Energy saving

OPTOTRONIC

®

+12Vset
Signal (Vset)
GNDset

Power lines

LED module

In combination with OSRAM LED power supplies, the

LEDset interface offers full fl exibility and a future-proof

system with the following features and benefi ts:

• Current setting

• Thermal protection

• High current accuracy

• Auxiliary supply 12 V

• Local dimming

• Simple wiring

Current
setting

• By resistor

Figure 1: LEDset application features.

Local
dimming

• With lin/log
potentio­meter

• StepDIM

Over­temperature
derating

Auxiliary
supply

• For control
logic (µc, IC)
on the LED
module

• For 12 V low­power LED
module

Constant
lumen output

5

LEDset SPECIFICATIONS

2. LEDset specifi cations

2.1. General overview

LEDset is a 3-wire analog control interface designed for

OPTOTRONIC

allows setting the output current of the electronic control

gear (ECG) by providing a highly accurate voltage reference

(Vset) to the ECG. Thanks to the control accuracy and sim-

plicity of LEDset, control gears become highly adaptable and

can cover a wide range of applications. The output current

can be set/dimmed by a passive device (e.g. resistor) or by

an external imposed-voltage control signal.

Moreover, the interface gives more freedom in the design of

customized systems by providing a stabilized 12 V auxiliary

voltage (+12Vset) that can supply an active circuit, for exam-

ple on the LED module, extending a simple temperature-

dependent current derating circuit to a more complex micro-

controller-based fl ux control.

®

constant-current LED power supplies. It

The main features of the LEDset interface can be

summarized as follows:

• Output current setting interface for constant-current ECGs

• 3-wire interface

– +12Vset: Stabilized 12 V auxiliary voltage (+/-10 %)
– Vset: Voltage reference in the range of 0 to 12 V (+10 %)
– GNDset: Ground reference of the LEDset interface

• Output current setting by analog input voltage control (Vset)

– For current setting, the Vset control voltage is within the

range of 10 V

– The LEDset characteristic is a fi xed relationship between

the Vset voltage and the percentage of the maximum

nominal current of the control gear (relative coding)

• High-output LED current accuracy

– Overall control system provides an Inom

of up to +/-5 %

– Accurate bias current generator on Vset for very precise

current setting via passive control (fi xed/variable resistor)

• 12 V auxiliary output (+12Vset) for the supply of electronic

ICs/circuits or the control of a fan (future extension)

• ECGs can be used in a wide power and current operating

range

tolerance

max

Figure 2: LEDset interface wiring (block diagram).

6

2.2. LEDset characteristic

LEDset SPECIFICATIONS

2.2.1. General description

With the LEDset interface, the output current can be defi ned

relative to the maximum nominal output current of the control

gear.

The basic relationship between the LEDset voltage (Vset)

and the ECG output current (Iout) is defi ned by the following

equation:

Iout Inom

max

(Vset 1)

9

where Inom

is the maximum nominal output current of

max

the ECG and Vset voltage is the voltage between Vset and

GNDset.

The relationship is valid for values of Iout that are within

the current range of the control gear, i.e. between Imin

and Inom

max

.

The generic Iout versus the Vset characteristic is shown in

fi gure 3.

Figure 3: Generic Iout vs. Vset characteristic.

Designation of lines:
Blue line: Ideal case
Orange line: Typical real ECG behavior with Imin

limitation and no turn-off capability

0 < Vset < Vmin

Vmin < Vset < 10 V

10 V < Vset < 11 V

11 V < Vset < +12 Vset (or Vset, open)

Table 1: LED output current as function of Vset.

Iout = lmin or lout = 0 (see chapter 2.2.2. for details)

Iout according to LEDset relationship

Iout = Inom

max

Iout = Imin (i.e. Iout = 0 if the ECG has a turn-off capability)

7

LEDset SPECIFICATIONS

Note:

Vmin is the Vset voltage value corresponding to the minimum

deliverable current (Imin) of the ECG. The Imin is specifi ed in

the datasheet of the applied ECG. Based on the LEDset rela-

tionship between Iout and Vset, it is possible to calculate the

typical Vmin of the ECG.

2.2.2. Implementation in the OSRAM ECG

Based on the general LEDset specifi cation, two different

LEDset implementations can currently be found in constant-

current OSRAM ECGs (for details, please refer to the data-

sheet of the specifi c product).

Example:

When using the OT 35/220-240/700 with a nominal current

of 700 mA, the minimum current is 100 mA (according to the

datasheet of the ECG) and the Vmin is as follows:

Vmin Vmin9 + 1 2.28 V

Imin

Inom

Basically, the two cases differ due to the minimum current

limitation of the ECGs. An ECG’s turn-off capability – rather

than the minimum current holding between Vmin and 0 V –

makes the difference between the cases.

The following diagrams describe the different cases imple-

mented in OSRAM LEDset ECGs:

Figure 4a: Case I. Figure 4b: Case II.

Product examples:
3DIM + LEDset (LT)

OT 45/220-240/700 3DIMLT E
OT 90/220-240/700 3DIMLT E

8

LEDset

OT 90/220-240/700 LT E

Product examples:
LEDset (LT) + current setting (CS)

OT 35/220-240/700 LTCS
OT 45/220-240/700 LTCS

2.3. Technical details

This chapter gives a general overview of the technical details

of the LEDset interface. For further details and deviations

from this basic information, please refer to the datasheet

and instruction sheet of the respective control gear.

LEDset SPECIFICATIONS

2.3.4. Insulation2.3.1. Bias current (Iset)

The LEDset interface is an active interface since the Vset in-

put can actually generate a constant current output (bias

current), allowing the Vset voltage to be achieved through

“passive” circuits (e.g. current setting by resistor, light sen-

sors etc.).

The integrated current generator provides a very stable bias

current (Iset) of 274 µA over the complete operating range of

the control gear. Thanks to this feature, unwanted current

variations due to temperature changes, which occur in many

ECGs with similar control interfaces, can be avoided.

2.3.2. +12Vset

The stabilized 12 V auxiliary voltage is able to supply a

current of up to 15 mA (laux). The voltage accuracy is within

a tolerance of ±10 %. A future power extension will provide

an even greater capability to supply more powerful loads

(such as an external fan for active cooling applications).

For details regarding the maximum allowable output power,

please refer to the datasheet and instruction sheet of the

respective control gear.

All ECGs with LEDset interface have the following minimal

insulation barriers:

Primary

circuit

Primary

circuit

Secondary

circuit

LEDset

Table 2: Insulation barriers of LEDset ECGs.

There is no galvanic insulation between the LEDset interface

and the secondary circuit.

Note: If the LEDset ECG is to be used in a system that must

be classifi ed as SELV (Safety Extra-Low Voltage), any circuit

connected to the LEDset interface of an SELV or SELV-

equivalent control gear can only be used if double-insulated

from the mains.

–

Depending

on the ECG

Depending

on the ECG

Secondary

circuit

Depending

on the ECG

–

No insulation

LEDset

Depending

on the ECG

No insulation

–

2.3.3. Fault protection

The +12Vset is protected against short circuit (+12Vset –

GNDset). Vset is protected up to the 12 V + 10 %.

The LEDset interface has no specifi c protection against elec-

trostatic discharge (ESD). Therefore, it is recommended that

any circuit (e.g. accessible potentiometer) connected to the

LEDset interface port has a proper insulation against touch-

able parts.

Moreover, the negative pole of the LED load (LED-) must not

be connected to the GNDset terminal.

9

LEDset SPECIFICATIONS

2.3.5. Color coding

The color coding for the connector of the LEDset interface is

defi ned as follows:

LED+ Red

LED-

LEDset GNDset Gray

LEDset Vset

LEDset +12Vset

Table 3: Color coding.

LED+ and LED- are the power outputs of the control gear.

The position and order of the terminals can vary between the

different LEDset ECG types.

Black

Violet

Blue

2.3.7. Fault conditions/troubleshooting

2.3.6. Cable length

The maximum length of LEDset cables should not exceed

2 m. Further limitations to cable length generally derive from

EMI emission or immunity issues or directly from product

specifi cation details. For detailed information, please refer to

the datasheet or instruction sheet of the respective LEDset

control gear.

2.3.7.1. Incorrect wiring 2.3.7.2. Missing control wire (Vset)

The LEDset interface has been designed to inherently pro-

tect itself and the LED module against incorrect wiring on the

secondary side of the control gear. Incorrect connections

between LED+ and Vset or GNDset can irreversibly damage

the ECG.

Other possible incorrect wirings on the secondary side do

not affect the operation of the ECG once they are removed

(irrespective of problems regarding the connected external

LEDset ECGs).

LEDset is an interface intended for the current setting and

thermal management of an LED module. If the Vset terminal

is not connected to the control unit, the thermal protection of

the LED module and its correct current setting will not work.

This fault condition may result in an undetected overheating

of the LED module. In order to protect the LED module in

this condition, the absence of a control signal (Vset open or

Vset ≥ 11 V) is detected and the ECG is shut down or set to

its minimum current (see fi gure 3).

10

LEDset SPECIFICATIONS

2.3.8. Connection of multiple ECGs

Depending on the LEDset control gear, the Vset signals can

be connected in parallel to set the current of multiple ECGs

by a resistor. This connection is allowed in case of a local

dimming application on a luminaire supplied by more than

one ECG.

In general, if n is the number of ECGs to be connected to-

gether to a local dimmer or current setting resistance, Rset/n

is the resistance value to be considered (where Rset is the

value needed to set the current of one single ECG).

Example: an offi ce luminaire with two ECGs locally dimmed

by a 22 kΩ potentiometer.

Figure 5 shows a parallel connection of two LEDset inter-

faces. The interfaces share a resistor Rset, with which it is

possible to set the output current. Current setting by external

resistor is explained in detail in chapter 3.1.1.

Figure 5: Parallel connection of two LEDset interfaces.

11

LEDset APPLICATIONS

3. LEDset applications

3.1. Current setting

3.1.1. Setting by external resistor

If the application requires a specifi c fi xed output current, the

easiest way to set the output current is to apply a resistor

between Vset and GNDset.

Figure 6: Current setting by external resistor.

As mentioned in chapter 2.3.1., the LEDset interface is an

active interface that is able to generate a constant current

output (Iset) and thus allows the use of “passive” circuits

(e.g. resistor) to achieve the setting voltage (Vset).

The resistor can be placed either on the terminal block of the

ECG or on the LED module (plug-and-play solution but with

two additional wires that have to be considered for cabling

design).

As a function of the LEDset interface, the Vset value is

related to the percentage of the ECG’s maximum nominal

current.

(Vset 1)

9

100

12

Iout

Inom

[%]

max

This means that the absolute value of the output current

depends on the maximum nominal current of the ECG.

Setting the output current Iout

700 mA will differ from setting the same Iout on an ECG with

Inom

= 1500 mA.

max

on an ECG with Inom

max

max

=

The following table shows the output current values obtained by applying

a 1 % resistor (from E96 series unless otherwise specifi ed) for two different

ECGs with a nominal current of 700 mA and 1500 mA, respectively.

LEDset APPLICATIONS

Rset – E96 series

Vset [V] Iout/Inom [%] Inom [mA] = 700 Inom [mA] = 1500
(unless otherwise
specifi ed)

0 0.0 0 0 0

3830 1.0 1 4 8

7500 2.1 12 82 176

11300 3.1 23 163 349

14700 4.0 34 235 505

15000 4.1 35 242 518

19100

20000 (E24)

5.2 47 329

5.5 50

348

706

747

21000 5.8 53 370 792

23200 6.4 60 417 893

25500

27000 (E24)

7.0 67 466

7.4 71

498

998

1066

28000 7.7 74 519 1112

30100 8.2 81 564 1208

34000

36500 (E48)

9.3 92 647

10.0 100 700 1500

1386

38300 > 10.0 100 700 1500

39000 (E24)

> 10.0 100

700 1500

40200 (and up to 60000) > 10.0 100 700 1500

Table 4: Current setting by external resistor.
For more information, please see the notes on page 14.

13

LEDset APPLICATIONS

Note 1: The E96 series covers a wide range of values. The

table contains only some sample values of this series. Please

check the standard E96 series to fi nd the value best suited

for meeting your current setting requirements.

Note 2: The values given above are calculated without con-

sidering the possible power and/or output voltage and/or

minimum output current limitations which depend specifi cally

on the output characteristics of the chosen ECG. Please

refer to the respective product datasheet.

Note 3: The resistor tolerance has an effect on the accuracy

of the current setting. Available standard tolerances are 5 %,

2 %, 1 %, 0.5 %, 0.25 % and 0.1 %. LEDset ECGs are de-

signed to provide up to 5 % of the overall control accuracy

(Rset – Iout) if Rset is a resistor with a tolerance of up to 1 %.

If higher than 1 %, the tolerance of Rset must be considered in

the Iout tolerance calculation.

Note 4: Since the Iset current value is very low, the power

rating of the resistor is not an issue to be considered when

selecting the resistor (considering a maximum value of

50 kΩ

Note 5: If the value of the commercial resistor differs too

much from the calculated resistance, connecting resistors in

series/parallel might help to obtain the precise required value.

Note 6: It is not recommended to set the Vset by dividing

the +12Vset voltage by a resistor divider. This setting is in

fact more complicated. Moreover, the stated accuracy toler-

ance of ±5 % for the overall control system may not be lon-

ger achieved because it is directly affected by the +12Vset

voltage tolerance which is ±10 %.

PRset = 3.8 mW).

Example:

This example is meant to help in choosing the most suitable commercial resistor for a given system.

The calculation applies to an OT 35/220-240/700 LTCS in LEDset confi guration to set an output current of 580 mA.

Starting from the basic relationship:

Vset 1 + 9 8.33 V

Iout

where Iout = 580 mA and Inom

= 700 mA

max

Inom

Therefore:

Rset 30.87 kΩ

Vset

where Iset = 274 µA

Iset

Looking at available values of commercial resistors (i.e. E96 series), 30.9 kΩ is the best choice.

The recalculated real current setting would be:

Vset

14

Rset

Iset

8.47 V

and therefore Iout = 580.7 mA

3.1.2. Step dimming (StepDIM)

Based on the previous chapter (3.1.1.), the current setting

by resistor can be easily extended by an additional step dim-

ming function. By switching between two external resistance

values, the output current can be changed to two different

levels (i.e. one to set the nominal current to 100 % and one

to step down to 40 %). Shorting the Vset to GNDset allows

turning off the LED module while the ECG is still supplied

with mains voltage.

LEDset APPLICATIONS

Possible solutions are shown in the following block diagram:

7a: Manual solution. 7b: Relay-based solution.

Figure 7: Step dimming by two resistor values.
For more information, please see the note on page 16.

15

LEDset APPLICATIONS

Switching can be carried out either by a switch (manual

activation, see fi gure 7a) or by using a relay (see fi gure 7b).

While Rset

resistance Rset

sets the current level Iout1, the equivalent parallel

1

(Rset1||Rset2) sets Iout2.

EQ

Note: In both cases (7a and 7b), two main issues need
to be considered when selecting the components:

• Performance

The relay contacts or switch contacts must be suitable for

applications with a very low current. Selecting the right

type (low contact resistance, oxidation-proof etc.), i.e.

golden-plated or bifurcated contacts, is therefore essential.

For a relay-based solution (see fi gure 7b) where the control

line is not galvanically insulated from the mains or the mains

potential, the following relays can, for example, be used:

• Safety/SELV (Separated or Safety Extra-Low Voltage)

In case of SELV systems, insulation between contact cir-

cuit and actuator part – the human fi nger (7a) or the coil

of the relay (7b) – must be considered. For example, if

the relay control line is in some way referred to the mains

potential, a double insulation must be provided between

the coil circuit and the contact side of the component so

that the SELV property of the system is ensured. In case

of a control line that is already double-insulated from the

mains, a standard low-cost signal relay can be used.

In any case, please refer to the safety standard EN
61347-2-13 for ECG requirements and to EN 60589-1
for luminaire requirements.

Control line
Supplier

OMRON

PANASONIC

Table 5: Step dimming by resistor – suitable relays.

230 V

AC

G2R1Z230VAC

G2R1AP3230VAC

Low voltage

G5V1 series (one contact pole)

G6S series (golden-plated – 3 V, 5 V, 12 V, 24 V)

PA(D)1a series (bifurcated – 3 V, 5 V, 12 V, 24 V)

The use of double-contact or/and bi-stable relays extend

the confi guration possibilities of the LEDset interface

(more current steps, pulse-based relay control line etc.).

16

3.2. Local dimming

3.2.1. Potentiometer application

If an application requires the dimmability of a luminaire, a sim-

ple and economical solution can be to implement a local dim-

ming function by a logarithmic or linear potentiometer. In this

case, the term “local dimming” refers to the possibility to set

the current of a single luminaire system by a potentiometer.

LEDset APPLICATIONS

Figure 8: Local dimming – potentiometer application.

The LEDset interface has been designed for the application

of standard potentiometers with standard rated resistances

of 47 kΩ or 50 kΩ and a tolerance of ±20 %.

Using a potentiometer with a nominal value within this range

allows dimming by changing the current from Inom

(at Vset > 10 V but less than 11 V) to 0 mA (at Vset < 1 V) or

higher, taking account of the Imin limit and the turn-off

capability (see cases I and II in chapter 2.2.2.).

Note 1: Potentiometers with nominal values lower than

47 kΩ - 20 % do not provide the complete dimmable range of

the output current. Nominal values higher than 50 kΩ + 20 %,

however, can enable the device to reach the range of Vset

max

> 11 V, changing the output current setting to Imin or 0 %

(see table 1).

Note 2: Local dimming means that the used dimming device

is a single-insulated potentiometer or a potentiometer that

is part of a multifunctional device and needs to be double-

insulated from the parts related to the mains potential if the

application is SELV-classifi ed (see general note on insulation

in chapter 2.3.4).

Suitable potentiometers for this application are for example:

• Vishay P16 NP 47K 20 % A (linear potentiometer)

• Vishay P10 YM AG 47K 5 % (medium-cost potentiometer)

• Tyco CB10KH473ME (low-cost potentiometer)

17

LEDset APPLICATIONS

3.2.2. Light sensor application

Daylight compensation can be easily obtained with the

LEDset interface by connecting existing commercial light

sensors (only plug-and-play sensors as described in the

3.2.2.1. Using OSRAM DIM MICO/PICO

DIM MICO/PICO is a light sensor from OSRAM which is

compatible with 1…10 V interfaces. The sensor works once

it is connected directly between Vset and GNDset.

This sensor is used to monitor, measure and maintain the

brightness level of its detection area to a preset value, which

is adjustable by a setpoint potentiometer screw. Once the

daylight decreases and the brightness of the area reaches or

falls below the preset value, the sensor starts to increase its

impedance between Vset and GNDset, thus increasing the

Vset voltage level. The higher current demand to the LEDset

ECG results in an artifi cial light compensation by the light of

the LED module.

following chapter). Light sensing can be approached by

using standard 1…10 V-compatible light sensors or by devel-

oping light sensors from IC chips and converting their output

signal to the Vset range of the LEDset interface.

Figure 9: Local dimming – light sensor application with DIM MICO/PICO.

Note: The 274 µA of Iset are enough to supply the sensor.

Particular attention should be paid to presetting the bright-

ness setpoint of the sensor, referring to the setup procedures

described in the DIM MICO/PICO datasheet. In any case,

Vset should be in the range of 10 to 11 V at the desired

maximum current output (no daylight present) to avoid

reaching the turn-off range of the LEDset interface charac-

teristic (see fi gure 4).

This warning does not apply if a LEDset ECG is used in

combination with a current set (CS) confi guration. For more

details, please see chapter 3.2.2.3. General notes on local

dimming: LEDset and “current set” combination.

For more detailed information about DIM MICO/PICO,

please refer to www.osram.com/lms-sensors

18

LEDset APPLICATIONS

3.2.2.2. Using customized sensors

Various light sensors can be used in place of the previously

mentioned OSRAM DIM MICO/PICO. Once the output

sensor is compatible with the LEDset interface, the resulting

control possibilities can perfectly fi t the needs of the appli-

cation.

In the following example, a light sensor is connected to a

microcontroller (MCU) before going to the Vset output signal,

introducing more fl exibility into the light management and,

at the same time, adding more managing possibilities (i.e.

temperature management as explained in chapter 3.3.2.5.

Application solution 5 – overtemperature management:

microcontroller (MCU) approach).

Please consider: When using a LEDset interface, the Vset

voltage range needs to be considered. Regardless of the used

sensor, the maximum Vset voltage should not exceed 11 V

(as described in chapter 2.2.1. General description) because,

otherwise, Imin or the turn-off condition (Iout = 0 mA) could

be reached.

For some ECGs, it is possible to exceed the 11 V in a specifi c

operation mode, while keeping the nominal output current

(Inom

) at its maximum value. This behavior is described in

max

the next chapter (3.2.2.3.).

Figure 10: Local dimming – light sensor – custom application.

19

LEDset APPLICATIONS

3.2.2.3. General notes on local dimming:
LEDset, “current set” combination

For some applications, the turn-off capability provided by

the LEDset characteristic above 11 V might not be an

appro priate feature.

Therefore, some LEDset ECGs can combine the LEDset

interface with the so-called “current set” (CS) feature.

Product examples are the OT 35/220-240/700 LTCS and

OT 45/220-240/700 LTCS (LTCS means “LEDset” (LT)

and “current set” (CS)).

On those devices, it is possible to set the current control

functionality by dip switch to work with a “pure” LEDset

interface as described in chapter 2, or to combine it with a

current set (CS) confi guration: 350, 500 and 700 mA where

the maximum nominal currents (Inom

The Vset signal can still be used to control/set the output

current of the ECG as in a “pure” LEDset control –

with the difference being only in regards to the Vset charac-

teristic above 11 V.

A typical characteristic of this confi guration is shown in

fi gure 11.

) can be selected.

max

20

LEDset APPLICATIONS

Figure 11: Local dimming – example of the LTCS characteristic of the OT 35(45)/220-240/700 LTCS.

Above 10 V and higher, the output current is maintained at

its maximum nominal value without turning off the ECG. In

this case, the accuracy features of the LEDset interface

can also be combined with infl exible light sensors with an

output range higher than 11 V. This capability to maintain

the Inom

ECG output easily solves possible issues.

Furthermore, the current set confi guration also allows the

ECG to continuously supply its Inom

input is left open (fl oating).

from 10 to +12 V +10 % without turning off the

max

current if the Vset

max

21

LEDset APPLICATIONS

3.3. Thermal derating

With its simple and fl exible properties, the LEDset interface

allows users to manage the LED module temperature directly

with the ECG.

Luminaire manufacturers prefer to customize their products

via different approaches to manage temperature deratings

and/or protections.

One-step (switch-off) or two-step (intermediate current level

and switch-off) solutions satisfy the simpler, more common

requirements for thermal protection/management (fi gures

12a and 12b). Besides, more sophisticated management so-

lutions need to control a continuous derating of the current

as a function of the temperature before turning off the LED

module (fi gures 12c and 12d).

Moreover, a different luminaire type, luminaire application or

a general luminaire maker approach always requires a specifi c

Iout vs. Tset (LED module temperature) characteristic in

terms of temperature thresholds and current values.

The LEDset interface allows users to strategically defi ne their

module temperature management, thus providing the possi-

bility to implement their own specifi c solution with

reliable accuracy.

Thanks to the auxiliary voltage output of the ECG (+12Vset),

simple and more sophisticated “active” solutions can be

realized and directly implemented on the LED module or on

a smart spot of the luminaire.

Providing an extremely high level of fl exibility and overall

accuracy, the LEDset interface is also suitable for emergency

applications where the fi ne-tuning is essential to ensure

safe and reliable operation at an ambient temperature of

up to 70 °C.

22

LEDset APPLICATIONS

Application solutions Complexity

level

a)

Low

Medium

b)

Low

Medium

c)

Medium

For detailed information,
please see chapters:

3.3.1. Overtemperature protection

3.3.1.1. Application solution 1 – TMP300 solution

3.3.1.2. Application solution 2 – LM26 solution

3.3.1.3. Application solution 3 – NPC SM6611 solution

3.3.1.4. Application solution 4 – SI S-5841 solution

3.3.1.5. Application solution 5 – MM3488 solution

3.3.2. Overtemperature protection (discrete NTC)

3.3.2.1. Application solution 1 – overtemperature protection by comparator

3.3.1. Overtemperature protection

3.3.1.6. Application solution 6 – TC620(1) solution

3.3.2. Overtemperature protection (discrete NTC)

3.3.2.2. Application solution 2 – overtemperature management
by comparator – two-step output

3.3.2. Overtemperature protection (discrete NTC)

3.3.2.3. Application solution 3 – overtemperature management:
continuous derating and switch-off

d)

e)

Figure 12: Thermal derating – overview of application solutions.

Very low

Medium/
high

3.3.2. Overtemperature protection (discrete NTC)

3.3.2.4. Application solution 4 – LEDset and current set
combination: direct NTC connetion

3.3.2. Overtemperature protection (discrete NTC)

3.3.2.5. Application solution 5 – overtemperature management:
microcontroller (MCU) approach

23

LEDset APPLICATIONS

3.3.1. Overtemperature protection

A possible approach for overtemperature protection is to

simply use the so-called “temperature switch ICs” – an easy,

relatively cheap and low-component-number solution.

3.3.1.1. Application solution 1 – TMP300 solution

TMP300 (Texas Instruments) is a digital output temperature

switch IC. Its voltage supply range is 1.8–18 V, therefore it

can be directly supplied by the LEDset +12Vset terminal.

The open drain output is to be connected to the Vset termi-

nal of the LEDset interface, thus obtaining the ECG shut-

The following chapters provide some example solutions of

different simple implementations realized by commercially

available ICs with integrated temperature sensing capability. A

schematic reference shows their interface with LEDset ECGs.

down when the temperature of the LED module exceeds a

certain Tset

The trigger temperature Tset

and +125 °C by an external resistor (Rtemp), calculated as

follows:

Rtemp

(temperature threshold).

TH

can be set between -40 °C

TH

10 (50 + Tset

TH

)

3

[kΩ]

Figure 13: Thermal protection – TMP300 solution.

For more information, please see the general notes on page 33.

24

The schematic of the circuit is shown in fi gure 13. Proper

by-pass capacitors (100 nF 25V X7R SMD type) should be

added on the supply line and Rtemp to ensure a noiseless

application.

The hysteresis of the temperature threshold can be set in

two different ways:

• 5 °C if pin 4 is grounded;

• 10 °C if pin 4 is connected to pin 6 (Vcc).

LEDset APPLICATIONS

A setting resistance (Rset) can be integrated into the

circuit in order to set the operating current of the system

as described in 3.1.1.

Example:

Conditions:

Iout = Inom

TsetTH = 80 °C

Rtemp 433 kΩ

max

10

(50 + TsetTH)

3

Form E96 series, a commercial value is 432 kΩ ± 1 %.

Based on this value, the

3 Rtemp

Tset

TH

10

79.6 °C50

Figure 14: TMP300 solution – output characteristic.

2

For Rset, a 39 kΩ ± 1 % will provide that Iout = 100 %

. Connecting pin 4 to the GNDset enables a hysteresis

Inom

max

of 5 °C. Figure 14 shows the resulting behavior of this circuit.

1

Figure 15: TMP300 solution – real circuit (1) appearance with connector
block (2).

25

LEDset APPLICATIONS

3.3.1.2. Application solution 2 – LM26 solution

LM26 (National Semiconductor) is a digital output tempera-

ture switch IC with a factory-programmed trip point ranging

from -55 °C to 110 °C (in increments of 1 °C). LM26 can have

four different confi gurations of the digital output. Version C

(active-high, push-pull on OS output) is needed for this appli-

cation.

In fi gure 16, a reference schematic is shown. Since the maxi-

mum operating voltage is limited to 5.5 V, a voltage regulator

is needed in order to supply LM26 from the LEDset interface.

The simplest solution is to clamp the supply voltage on pin 4

with a Zener diode (D

current to the diode, a proper value of R

). In order to ensure a suffi cient reverse

1

has to be selected.

1

A by-pass capacitor (C1) between pin 4 and ground (pin 2) is

recommended.

Figure 16: Thermal protection – LM26 solution.

The hysteresis of the temperature threshold can be set at:

• 10 °C if pin 1 is grounded;

• 2 °C if pin 1 is connected to pin 4 (Vcc).

The LM26 digital output drives a transistor (Q

) which pulls

1

the Vset node down when an overtemperature condition is

detected. Q

can either be a bipolar or a logic-level FET de-

1

vice with a voltage rating above 12 V. A device with low leak-

age current (namely lower than 1 µA) is mandatory. For this

reason, bipolar transistors are preferred (i.e. BC847).

For more information, please see the general notes on page 33.

26

Figure 17: LM26 solution – output characteristic.

2

1

Figure 18: LM26 solution – real circuit (1) appearance with connector
block (2).

LEDset APPLICATIONS

3.3.1.3. Application solution 3 – NPC SM6611 solution

SM6611 (NCP) is a temperature switch IC able to change

the state of an output pin (invert) when the chip temperature

exceeds a preset temperature (Tset

ture detection is managed by hysteresis (10 °C) to prevent

unstable output switching (sensed temperature close to the

preset temperature). SM6611 series propose 6 preset Tset

temperatures, 2 output confi gurations (push-pull, open drain).

). The TsetTH tempera-

TH

TH

In fi gure 19a, a reference schematic is shown. The maximum

operating voltage of the IC is +15 V and the open drain

output can withstand 10 V maximum. The control could be

directly used as in fi gure 19a. A safer implementation is

shown in fi gure 19b where the output pin is connected to

the Vset via transistor (in case of a voltage higher than 10 V).

A maximum leakage current of 1 µA on the open drain

output allows the use of the IC without affecting the control

accuracy (over the Iset).

Figure 19a: Thermal protection – SM6611 solution. Figure 19b: Thermal protection – SM6611 solution.

Example:

Considering a Tset

of 75 °C, the following devices can

TH

be used:

• SM6611DAH in case of direct connection to LEDset

(case a – not recommended)

• SM6611DBH in case of direct connection to LEDset via

transistor (case b)

For more information, please see the general notes on page 33.

27

LEDset APPLICATIONS

3.3.1.4. Application solution 4 – SI S-5841 solution

The SI S-5841 (SI – Seiko Instruments Inc.) series is a tem-

perature switch IC which detects a certain temperature and

sends a signal to an external device. Various combinations

of the parameters such as the detection temperature, output

form and output logic can be selected.

In package SOT-23-5, fi ve Tset

as factory settings (+55 °C, +65 °C, +75 °C, +85 °C, +95 °C).

The temperature hysteresis is set by the HYS1 pin (and/or

HYS2 pin), offering the choice between four values: 0 °C,

2 °C, 4 °C, 10 °C (the confi guration depends on ordering part

number and package type).

More than the previous ICs, the S-5841 series also has a

noise suppression time (t

temperatures are available

TH

). If the temperature is lower than

delay

the detection temperature (+TD), the DET pin is at a low level.

Although the output from the comparator goes active due to

noise if the period in which this status continues is shorter

than the noise suppression time, the DET pin keeps its low

level. However, if the period in which the output of the inter-

nal comparator is active is longer than the noise suppression

time, the DET pin is set to a high level. In case of +12 V

range supply voltage, the noise suppression time is about

1.2 –1.5 s.

In fi gure 20a, a reference schematic is shown. The maximum

operating voltage of the IC is +12 V and the open drain

output can withstand 12 V maximum. The control could be

directly used as in fi gure 20a. By the way, a safer and highly

recommended implementation is shown in fi gure 20b where

the output pin is connected to the Vset via a transistor and

the supply voltage is simply reduced by a Zener diode and a

resistor (+12 V can have a tolerance of +10 %).

Figure 20a: Thermal protection – S-5841 solution (direct connection).

A maximum leakage current of 1 µA on the open drain output

allows the use of the IC without affecting the control accuracy

(over the Iset).

For more information, please see the general notes on page 33.

28

Figure 20b: Thermal protection – S-5841 solution (via output transistor and voltage regulator).

Example:

Considering a Tset

of 75 °C and a hysteresis of 4 °C,

TH

the following devices can be used:

• S-5841B75D-M5T1U (open drain) in case of direct

connection to LEDset (case a – not recommended)

• S-5841B75A-M5T1U (CMOS out) in case of connection

to LEDset via transistor (case b)

In both cases, pin 1 must be tied to Vcc (pin 4).

LEDset APPLICATIONS

3.3.1.5. Application solution 5 – MM3488 solution

The MM3488 (MITSuMI) is a temperature switch IC that

changes the IC output level from “low” to “high” when the

temperature around the IC reaches the detection tempera-

ture. With the hysteresis function (5 °C, 10 °C, 15 °C), the IC

output level returns to “low” when the ambient temperature

drops to the temperature hysteresis selected after detection.

Detection temperature Tset

1.0 °C between 60 and 90 °C with rank expansion (available

as factory-trimmed value), with a detection temperature

accuracy of ±2.0 °C.

The very-small-outline package SSON-4B allows saving

space on the LED module, compensating for the higher

can be selected in steps of

TH

overall number of components with respect to the previous

solutions.

A noise rejection time t

between 250 and 500 µs allows

noise

debouncing the temperature signal, preventing unstable out-

put switching caused by possible noise.

In fi gure 21, a reference schematic is shown. Since the maxi-

mum operating voltage is limited to 5.5 V, a voltage regulator

is needed in order to supply the MM3488 via the LEDset

interface. The simplest solution is to clamp the supply volt-

age with a Zener diode (D

reverse current to the diode, a proper value of R

selected. A by-pass capacitor (C

). In order to ensure a suffi cient

1

has to be

1

) between pin 4 and ground

1

(pin 2) is recommended.

D

= 5 V1 5 % signal Zener diode (i.e. NXP BZT52H-C5V1)

1

C

= 100 nF 25 V 10 % X7R 0603

1

Q

= NPN signal transistor (BC847)

1

R

= 1K 5 % 0603

1

R

= 10K 5 % 0603

2

R

= 100K 5 % 0603

3

Figure 21: Thermal protection – MM3488 solution (via output transistor).

Since the IC output is only an open drain, a pull-up resistor

is needed.

For more information, please see the general notes on page 33.

Example:

Considering a Tset

of 75 °C and a hysteresis of 5 °C,

TH

the following device can be used:

• MM3488575RRE

29

LEDset APPLICATIONS

3.3.1.6. Application solution 6 – TC620(1) solution

The TC620 and TC621 (from Microchip) are programmable

logic output temperature detectors designed for use in ther-

mal management applications. The TC620 features an on-

board temperature sensor, while the TC621 connects to an

external NTC thermistor for remote sensing applications.

Both devices feature dual thermal interrupt outputs (“high

limit” and “low limit”), each of which is programmed with a

single external resistor. With the TC620, these outputs are

driven active (high) when the measured temperature equals

the user-programmed limits. The CONTROL (hysteresis)

output is driven high when the temperature equals the “high

limit” setting and returns to “low” when the temperature falls

below the “low limit” setting. This output can be used to pro-

vide “on/off” control to a cooling fan or heater. The TC621

provides the same output functions, except that the logical

states are inverted.

Below, an application example using the TC620 is given.

Thanks to the two programmable temperatures, it is possible

to set an intermediate current level before turning the LED

module off completely.

C1 = 100 nF 25 V 10 % X7R 0603
Q

, Q2 = NPN signal transistor (i.e. BC847)

1

R

= 330 kΩ 5 % 0603

2

R

= 330 kΩ 5 % 0603

3

Figure 22: Thermal derating – TC620 solution.

For more information, please see the general notes on page 33.

30

Rset
Rset
R
RLS

1

2

see example on the right

HS

LEDset APPLICATIONS

Figure 23: TC620 solution – output characteristic. Figure 24: TC620 solution – R

Example:

Conditions:

Tset

= 80 °C IoutH = 0 % Inom

H

TsetL = 70 °C IoutL = 70 % Inom

max

max

With the TC620 datasheet, it is possible to calculate the

resistance value for the temperature trip points:

2.1312

R

TRIP

0.5997 T

(see fi gure 24)

Therefore:

R

= 161.5 kΩ

HS

In order to achieve the 70 % of Inom

lel resistance Rset

EQ

about 26.7 kΩ (see table 4 in chapter 3.1.1.).

Rset

Rset

Rset

EQ

2

1

Rset1 + Rset

1

Rset

Rset

Rset1 Rset

Recalculating, the real Iout = 70.2 % of Inom

RHS = 162 kΩ (E96 1% series) TsetH = 80.6 °C

vs. temperature.

TRIP

, the equivalent paral-

max

(Rset1||Rset2) to be chosen must be

Rset

2

26.7 kΩ

2

EQ

61.8 kΩ

EQ

Rset2 = 61.9 kΩ

(E96 1 % series)

.

max

R

= 151.9 kΩ

LS

RLS = 150 kΩ (E96 1% series) TsetL = 68.8 °C

Regarding Rset resistor:

Rset

= 47 kΩ 1 % (100 % of Inom

1

– see chapter 3.1.1.)

max

31

LEDset APPLICATIONS

Note: For a precise calculation, the V
BC847 transistor, the voltage drop is in the range between 40 and 50 mV depending
on the temperature of the device. In fi gure 25, the voltage drop relates to a temperature
range between -55 and +150 °C. In the described application solution, however, the
temperature of Q
voltage drop variation will be smaller than in fi gure 25.

The Rset

is generally within a tighter range when it is active. Therefore, the

2

model should be as follows:

EQ

of Q2 should also be considered. For a

CEsat

Considering the calculated Rset1 and Rset2 and introducing a

voltage drop of Q1 = 45 mV :

BC847B; l
(1) T
(2) T
(3) T

Figure 25: BC847 – collector-emitter saturation voltage vs. collector current
(NXP reference data).

= 150 °C.

amb

= 25 °C.

amb

= -55 °C.

amb

C/lB

= 20.

Rset

Iset + V

Vset 7.37 V

2

Rset

1 +

Rset

CEsat

2

1

and therefore Iout = 70.4 % of Inom

The error introduced by the transistor affects the overall control

accuracy of the ECG by about 0.2 % (to be added to the 5 % of the

ECG itself). The severity of the error depends on the working point

and the transistor Vce. Choosing a lower output current increases

the severity of the error (i.e. Iout = 35 % of Inom

32

0.3 %).

max

max

3.3.1.7. General notes on IC temperature switches:
choice and usage

• For all the above application solutions, the Rset can be

either a fi xed resistor or a variable resistor usable for local

dimming (as described in 3.2.).

LEDset APPLICATIONS

• For all the above application solutions except application

solution 6, the output of the IC (direct output or output via

transistor) can be connected to the Vset line via an Rset

resistor. In this way, in case of overtemperature, the output

current can be set to a percentage of Inom

instead of

max

completely switching off the LED module as shown in the

example cases. Application solution 6 allows implementing

both conditions, partial load and switch-off control.

• When choosing IC temperature switches, the following

issues must be considered:

– Leakage current of the output stage of the control

module: In case of an open-drain output solution directly

connected to Vset, the leakage current should be as low

as possible (10 µA already lead to an error of 3 %) in

order not to affect the overall control accuracy.

– Supply voltage: If the IC cannot withstand the +12 V,

a voltage regulator must be used.

– Supply current: In LEDset ECGs of the fi rst generation,

the supply current provided by the +12Vset terminal must

be kept lower than 15 mA.

– Transistor output solution:

- Suitable if the maximum voltage of the output pin of the

IC cannot withstand the maximum Vset that applies to

the respective application.

- Suitable if the leakage current of the output pin of the

IC becomes too high (a leakage current of more than

10 µA affects the overall control accuracy of the ECG by

3 % (to be added to the 5 % of the ECG itself).

2

Figure 26: Two-step solution without switch-off.

33

LEDset APPLICATIONS

3.3.2. Overtemperature protection (discrete NTC)

The application solutions analyzed in 3.3.1. show the imple-

mentation of the LED module’s overtemperature protection

by means of a dedicated IC chip that integrates the tempera-

ture sensing. Similar results can be achieved by implementing

electronic circuits based on a discrete NTC component and

an OPAMP (operation amplifi er) which acts like a comparator.

Benefi ts of this solution:

• The cost of the circuit components is lower.

• In some applications, the sensing component needs to be

placed very close to the LED or in other places where

3.3.2.1. Application solution 1 –
overtemperature protection by comparator

This chapter shows how an overtemperature protection

circuit can be implemented by using an OPAMP IC in posi-

tive feedback confi guration (acting like a comparator).

space can be a problem. The use of a discrete NTC

(i.e. an SMD NTC) can solve this issue.

• It allows the implementation of continuous derating

functions (not only steps of Iout).

Drawbacks:

• The NTC resistance variation needs to be converted into a

useful signal according to the operating range of the Vset

characteristic. This implies the need for a higher number of

(low-cost) components.

• Depending on the complexity, the tuning of the circuit de-

sign needs more time, especially concerning the variation

of the Vset output with respect to the tolerance of the dis-

crete components used.

Figure 27: Thermal derating – NTC + OPAMP solution. Figure 28: NTC + OPAMP solution – output characteristic.

34

The circuit confi guration allows setting a hysteresis bet ween

on and off state, thus avoiding spurious and unwanted light

fl ickering/toggling: focusing on the comparator circuit, the

R

, R4 and R3 resistors set the trip threshold voltages V

1

(related to Tset

TH

- ΔT

Hyst

) and V

- (related to TsetTH).

TRIP

TRIP

+

LEDset APPLICATIONS

These V

related to the divider realized by the R

voltages are compared with the voltage

TRIP

and NTC resistors.

2

Based on the NTC characteristic (resistance vs. temperature)

and the pull-up resistor (R

the circuit to customer needs. Once the V

the NTC) becomes higher than V

goes to low state. Consequently, Q

in this case), it is possible to tune

2

(voltage across

NTC

+, the comparator output

TRIP

opens and the LED

1

module is supplied by the current which has been set by the

Rset resistance.

However, when V

of the comparator turns on Q

becomes lower than V

NTC

and thus the Iout becomes

1

-, the output

TRIP

0 mA.

Example:

Requirements:

Tset

= 76 °C

TH

ΔT

= 6 °C

Hyst

Iout = Inom

Iout

fault

max

= 0 mA

2

1

By selecting the following components,
the result shown in fi gure 30 can be achieved:

= 100 kΩ 0603 1 % (general purpose)

R

1

R

= 270 kΩ 0603 1 % (general purpose)

2

R

= 560 kΩ 0603 1 % (general purpose)

3

R

= 36 kΩ 0603 1 % (general purpose)

4

Rset = 39 kΩ 0603 5 % (general purpose)
R

= NTCS0805E3683GXT (680 kΩ 2 % 0805) (glass-protected – Vishay)

NTC

U

= LM2904M – SO8 (general purpose)

1

Q

= BC847 – SOT23 (general purpose)

1

C

= 100 nF X7R 0603 (general purpose)

1

(by-pass capacitor to be placed as close as possible to the power pins of U1)

Figure 29: NTC + OPAMP solution – real circuit (1) appearance with
connector block (2).

Figure 30: Thermal derating – NTC + OPAMP solution (example).

35

LEDset APPLICATIONS

3.3.2.2. Application solution 2 –
overtemperature management by comparator: two-step output

The following application is basically similar to the one described in

chapter 3.3.1.6. Application solution 6 – TC620(1) solution. The

circuit is obtained by using a low-cost dual OPAMP, which allows

setting two trip temperatures (Tset

hysteresis by extending the circuit functionality described in chapter

3.3.2.1. Application solution 1 – over temperature protection by

comparator.

and TsetL) and their relative

H

Figure 31: Thermal derating – NTC + OPAMP solution: two-step output – schematic. Figure 32: NTC + OPAMP solution: two-step output – characteristic.

36

Example:

Requirements:

Tset

= 70 °C

H

Tset

= 55 °C

L

ΔT

= 5 °C

Hyst

LEDset APPLICATIONS

Iout = Inom

Iout

warning

Iout

fault

max

= 60 % Inom

= 0 mA

max

By selecting the following components,
the result shown in fi gure 33 can be achieved:

R1 = 68.1 kΩ 0603 1 % (general purpose)
R

= 270 kΩ 0603 1 % (general purpose)

2

R

= 560 kΩ 0603 1 % (general purpose)

3

R

= 20.5 kΩ 0603 1 % (general purpose)

4

R

= 560 kΩ 0603 1 % (general purpose)

5

R

= 36 kΩ 0603 1 % (general purpose)

6

Rset

= 18 kΩ 0603 1 % (general purpose)

1

Rset

= 22 kΩ 0603 1 % (general purpose)

2

R

= NTCS0805E3683GXT (680 kΩ 2 % 0805) (glass-protected – Vishay)

NTC

U

= LM2904M – SO8 (general purpose)

1

Q

, Q2 = BC847 – SOT23 (general purpose)

1

C

, C2 = 100 nF X7R 0603 (general purpose)

1

(by-pass capacitor to be placed as close as possible to the power pins of U1)

Notes:

• Rset = Rset

• The dividing rate between Rset

+ Rset2 sets the Inom.

1

1

and Rset2 allows adjusting the Iout

warning

output level.

• The distribution of the resistance values of R
adjusting the Tset

• Adjusting the values of R

Δ

T

(in principle, ΔT

Hyst

and TsetL temperature trip thresholds.

H

(for TsetH) and R3 (for TsetL) allows changing the respective

5

can be set with different values for TsetH and TsetL).

Hyst

Increasing the resistance value decreases the

, R4 and R6 allows setting and

1

Δ

T

and vice versa.

Hyst

Figure 33: Thermal derating – NTC + OPAMP solution: two-step output (example).

2

1

Figure 34: NTC + OPAMP solution: two-step output – real circuit (1)
appearance with connector block (2).

37

LEDset APPLICATIONS

3.3.2.3. Application solution 3 –

overtemperature management: continuous derating and switch-off

The following application shows a cost-effi cient solution obtained by using a low-

cost dual OPAMP (such as LM2904). The idea is to manage the overtemperature

state of the LED module by continuously derating the current in a defi ned temp e-

rature range (from Tset

current when the protection temperature is reached (Tset

to TsetH), ending with the switch-off of the supply output

L

). The design of the

H

circuit becomes a bit more complicated but the solution is very cheap and only

requires about 15 components which do not take up a lot of space.

Figure 35: Thermal derating –
NTC + OPAMP solution: continuous derating and switch-off.

38

Figure 36: Thermal derating –
NTC + OPAMP solution: continuous derating and switch-off characteristic.

Example:

Requirements:

Tset

= 75 °C

H

Tset

= 60 °C

L

ΔT

= 5 °C

Hyst

LEDset APPLICATIONS

Iout = Inom

Iout

warning

Iout

fault

max

= from 100 % to 60 % Inom

= 0 mA

in a linear way

max

By selecting the following components,
the result shown in fi gure 37 can be achieved:

R

= 100 kΩ 0603 1 % (general purpose)

1

R

= 270 kΩ 0603 1 % (general purpose)

2

R

= 0R 0603 1 % (general purpose)

3

R

= 681 kΩ 0603 1 % (general purpose)

4

R

= 36.8 kΩ 0603 1 % (general purpose)

5

R

= Not mounted (general purpose)

6

Rset

= 18 kΩ 0603 1 % (general purpose)

1

Rset

= 22 kΩ 0603 1 % (general purpose)

2

Rset

= Not mounted

3

R

= NTCS0805E3683GXT (680 kΩ 2 % 0805) (glass-protected – Vishay)

NTC

D

= 1N4148 (general purpose)

1

U

= LM2904M – SO8 (general purpose)

1

Q

= BC847 – SOT23 (general purpose)

1

C

, C2 = 100 nF X7R 0603 (general purpose)

1

(by-pass capacitor to be placed as close as possible to the power pins of U1)
C3 = 1 nF COG 0603 (general purpose)
(by-pass capacitor to be placed across D1)

Notes:

• Rset = Rset

• The dividing rate between Rset

+ Rset2 sets the Inom.

1

1

and Rset2 allows adjusting the Iout

output slope

warning

level.

• The distribution of the resistance values of R
adjusting the Tset

• Moving the values of R
resistance value decreases the

and TsetL temperature trip thresholds.

H

allows adjusting the respective ΔT

4

Δ

T

Hyst

, R2 and R5 allows setting and

1

and vice versa.

. Increasing the

Hyst

Figure 37: Thermal derating – NTC + OPAMP solution: continuous derating and
switch-off characteristic (example).

2

1

Figure 38: NTC + OPAMP solution: continuous derating and switch-off –
real circuit (1) appearance with connector block (2).

39

LEDset APPLICATIONS

3.3.2.4. Application solution 4 –

LEDset and current set combination: direct NTC connection

As described in chapter 3.2.2.3. General notes on local dimming: LEDset,

“current set” combination, there are ECGs which can combine the LEDset inter-

face characteristic with the optional current set confi guration. ECGs with this kind

of combination offer another very simple and economical application: the direct

connection of an NTC. Additional resistors named Rs and Rp can be used to fi ne-

tune the Tset

and the linearization of the characteristic above the TsetTH.

TH

Figure 39: Thermal derating – direct NTC connection. Figure 40: Direct NTC connection – output characteristic.

40

For this kind of application, the choice of the NTC is funda-

mental to meet the requirements in terms of the Tset

TH

(temperature from which to start the derating) and the slope

rate (based on the NTC parameters B25/85 and B25/100) of

the characteristic Iout vs. Tset above the Tset

. For the fi ne

TH

tuning, the Rp resistor allows changing the TsetTH point to

reach the temperature required to start the derating.

LEDset APPLICATIONS

Example:

The following example shows the result that can be achieved

by using a standard SMD NTC component from a well-known

NTC thermistor producer.

Rs = 0 Ω (short circuit only)
R

= NCP15WM474J03RC

NTC

(470 kΩ 3 % B25/85 = 4582 - 0805 - Murata)

Two curves are shown to highlight the effect of the Rp resistor on the
determination of the Tset

= 270 kΩ 0603 1 % (general purpose)

Rp

1

Rp

= 120 kΩ 0603 1 % (general purpose)

2

. The following Rp values have been used:

TH

Figure 41: Thermal derating – direct NTC connection (example).

41

LEDset APPLICATIONS

3.3.2.5. Application solution 5 – overtemperature

management: microcontroller (MCU) approach

Since the cost of small 8-bit microcontrollers has dropped

over the past years, they have become an affordable solution

for implementing simple functionalities and increasing the

fl exibility of a system at the same time. These microcon-

trollers are equipped with various kinds of peripherals, e.g.

A/D converters (8–10 bits), which allow the measurement of

analog input coming from an NTC, as well as a light sensing

circuit. I2C or UART-embedded HW peripherals allow ex-

changing data via a communication bus or interfacing other

ICs (e.g. light sensors such as SFH7770 can be directly con-

nected via I2C bus).

In terms of temperature/overtemperature management,

this type of MCU (e.g. Microchip PIC12F1822 or Atmel

Tiny25/45) offers a high level of fl exibility as it can be

programmed to achieve different goals:

Different NTC sensors can be interfaced by saving different

NTC characteristics in the MCU memory.

• The NTC signal can be “transformed” into Vset output (and

therefore Iout) via a very fl exible and fully customizable relation.

• Some MCUs, e.g. the types mentioned on the left, have an

embedded temperature sensor which can be used to eval-

uate the temperature of the LED module. In this way, it is

possible to save MCU resources/pins for other functions

such as sensing inputs.

• Information on the LED module and the luminaire, e.g.

current temperature value, set-up parameters and warning

temperature, can be communicated to the user in various

smart ways: via digital bus (by wire), by infrared receiver

and transmitter or by using an LED coding approach (e.g.

turning a dedicated LED on and off at a certain frequency).

• The LED module itself can be used to warn the user in

advance of a possible overtemperature problem. For this

purpose, the LED module can be put into “blinking” mode

by turning the light on and off or switching it between its

maximum and minimum level (see fi gure 43).

This MCU approach is illustrated by the schematic diagram

on the right.

42

LEDset APPLICATIONS

Note:

The DAC interface can be implemented in various ways. The only

thing to take into account is that the DAC circuit must be able to

sink the Iset current (274 µA) imposed by the Vset connection.

Figure 42: Thermal derating – MCU solution.

A simple voltage regulator is required to regulate the +12Vset to 5 V which
are needed to supply the MCU.

The voltage divider R
The middle point of the divider is connected to an A/D channel of the MCU.

/NTC is connected to the same 5 V supply as the MCU.

2

On the output side, the PWM output used to generate the

Vset is connected to a fi lter (active or passive) to rectify the

signal. In the example (fi gure 42), only a general DAC inter-

face block is shown. DAC output is sensed by an A/D chan-

nel of the MCU, thus controlling the Vset output in a closed-

loop system, which ensures the highest accuracy of the output.

In the MCU memory (ROM or EEPROM if present), the NTC

divider characteristic can be stored as a lookup table. Here

are some notes on this:

• The higher the number of the stored points, the more ac-

curate is the output of the measurement.

• If the measured temperature is between two points, an in-

terpolation can be used.

• The number of lookup table points should be higher in the

region of interest (i.e. if the overtemperature is 70 °C, the

number of points should be higher between 60 and 80 °C).

• A higher AD resolution improves the accuracy of the mea-

surement but also affects the memory resources.

• A little digital fi lter should be applied on the AD raw values

if no external hardware fi lter is used on this input (RC fi lter).

Once the fi ltered AD

count value is translated into a tempera-

1

ture value by the stored temperature lookup table, the Vset

reference value must be generated. For converting the tem-

perature value into a Vset value, another lookup table (e.g.

Vset lookup table) has to be used.

The output result is used as a reference to generate the duty

cycle of the PWM channel corrected by the feedback com-

ing from the AD

channel.

2

43

LEDset APPLICATIONS

Using two lookup tables – one for the temperature and one

for the Vset – allows the designer to be very fl exible:

• The NTC can be changed by modifying only the points of

the temperature lookup table.

• The Vset output characteristic can be changed (e.g. when

the temperature monitor system is used for a different lumi-

naire) by modifying only the points of the Vset lookup table.

• By storing more than one lookup table for the temperature

and the Vset (the only limitation is the available memory

size), more applications can be covered by the same MCU

and the same fi rmware. In this case, the correct table con-

fi guration has to be selected by pulling one or more MCU

pins at +5 V or GND.

• Since the Vset output is generated digitally by the MCU,

it is possible to toggle it between two values in a certain

temperature range and with a chosen frequency (low

enough to be far from the cut-off frequency of the pass

band of the used ECG), generating a light toggling if nec-

essary. The example below (fi gure 43) shows a possible

implementation. Reaching the determined temperature be-

fore the overtemperature protection value, a toggling be-

tween two current levels (e.g. 100–50 % or 100–0 %) al-

lows the luminaire to warn the user about a possible shut-

down situation.

• A simpler way to signalize the LED module status can be

provided by a small colored LED (e.g. blue LED) connected

to a general-purpose output pin of the MCU. This LED can

be placed directly on the LED module or somewhere else

in the luminaire.

• A UART communication interface (see fi gure 44) realized

by an IR emitter diode and an IR transistor receiver (e.g.

SFH320FA) allows the digital communication of the lumi-

naire status and enables the manufacturer to customize

the luminaire directly at the end of the production line (i.e.

by downloading the lookup tables) or even to upgrade the

luminaire system behavior after installation (see fi gure 45).

Moreover, the IR emitter diode and IR transistor receiver

can be placed directly on the LED module (option 1) or in

a different, more convenient space of the luminaire system

(option 2).

Figure 43: Example of overtemperature warning by LED module toggling.

44

LEDset APPLICATIONS

Figure 44: Thermal derating – MCU solution: module status signaling by an LED. Figure 45: MCU solution: module status signaling/communication by IR interface.

The MCU approach can be a bit more expensive and may

require more design development skills (need of HW and

SW development) compared to the application solutions

discussed earlier in this chapter. However, together with

OSRAM ECGs equipped with LEDset interface, it signifi cantly

increases the customizability and fl exibility of the luminaire

system.

45

LEDset APPLICATIONS

3.4. +12Vset auxiliary supply

3.4.1. Aesthetic use

The LEDset interface provides a +12Vset supply voltage that

can be used in different ways: not only for thermal manage-

ment, daylight compensation and aging compensation, but

also for aesthetic purposes.

In addition to supplying the circuits shown above, the

+12Vset supply voltage can also be used for some “low-

power” LED applications, e.g. ring backlighting of a luminaire

switch (see fi gure 48).

Figure 46: +12Vset auxiliary supply – aesthetic use. Figure 47: +12Vset auxiliary supply – aesthetic use, controlled LEDs.

CHIPLED or TOPLED low-power LEDs can be supplied by

connecting them directly to the +12Vset via a resistor (see

fi gure 46) or, in case of an MCU application, via a MOSFET/

transistor that can add a blinking feature or a smooth pulsing

solution (by using a PWM output of the MCU; see fi gure 47).

A ring-shaped light guide, for example, can create very nice

aesthetic effects without requiring an additional power supply.

46

Figure 48: Application example:
ring backlighting of a luminaire switch.

3.4.2. Active cooling

Future generations of the LEDset interface might have a

higher power capability via the +12Vset auxiliary supply.

It will then be possible to drive an active cooling system

such as a fan (e.g. when high-power LED modules require

forced cooling). The following block diagram shows such

an application.

LEDset APPLICATIONS

Figure 49: +12Vset auxiliary supply – active cooling system.

The power supplied by the +12Vset auxiliary supply and thus

the cooling capability of the fan can be regulated by an ex-

ternal electronic control circuit, with the LED module temper-

ature being used as control signal. This feature can be easily

and fl exibly integrated with a small MCU on the LED module.

Please refer to the datasheet of the LEDset product and

verify that the current capability of the +12Vset auxiliary

supply matches the selected fan requirements.

47

LEDset APPLICATIONS

3.5. Constant lumen output

The application example in chapter 3.3.2.5. Application

solution 4 – overtemperature management: microcontroller

approach shows that – in addition to the thermal manage-

ment of the module – more features can be added thanks

to the presence of the MCU:

• By using a general-purpose timer of the MCU, it is possible

to measure the working time of the module and store it to

memory.

• The real-time temperature measurement allows the appli-

cation of a “temperature weight” to properly estimate the

lifetime of the module.

• The knowledge of the real supply current of the LED mod-

ule allows the application of a “current weight” to properly

estimate the lifetime of the module.

Figure 50: Aging compensation: characteristic of concept.

48

By estimating the lifetime of the module with the mentioned inputs (estimation algo­rithms are not within the scope of this application guide), it is possible to increase
the nominal output current of the ECG to a certain degree (up to its maximum limit)
by increasing the Vset control voltage, thus compensating the aging effects of the LED
module as shown by the orange line in fi gure 50 (the dashed gray line illustrates the
luminous fl ux decrement that occurs if the aging effects are not compensated).

The concept explained above can be implemented by storing a constant-lumen lookup
table in the MCU memory. By entering the working time of the module (e.g. in kHours),
it is possible to achieve the increase in Vset control voltage required to compensate the
aging effects of the LED module. The working time can be regularly saved in the MCU
memory (e.g. EEPROM), thus providing an accurate estimation of the lifetime.

LEDset APPLICATIONS

3.6. Combination of features

With LEDset, some LED control features can be combined

with one single interface. Figure 51 gives an overview of pos-

sible combinations. OSRAM will assist you in creating your

own specifi c solution.

Features that can be combined:

• Temperature control

• Daylight sensing

• Local dimming by potentiometer

(connected to the control module)

• Use of external switch for on/off switching

(e.g. capacitive touch key)

• Aging compensation

• Auxiliary LED signaling

• Auxiliary IR communication

Figure 51: Combination of LED control features by MCU via LEDset interface.

49

www.osram.com/ledset

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