International Rrectifier IRPLCFL8U User Manual

IRPLCFL8U

Simplified Three Level Dimming CFL Fluorescent

Ballast using the IRS2530D DIM8

Table of Contents

1. Features ...........................................................................................2

Page

2. Overview ..........................................................................................2

3. Circuit Schematic ............................................................................. 8

4. Electrical Characteristics ..................................................................9

5. Fault Protection Characteristics ....................................................... 9

6. Functional Description....................................................................10

7. Fault Conditions .............................................................................15

8. Ballast Design ................................................................................19

9. Bill of Materials...............................................................................22

10. IRPLCFL8U PCB Layout..............................................................23

11. Inductor Specifications .................................................................27

www.irf.com

RD0803

- 1 -

1. Features

 Drives 1 x 32W Spiral CFL Lamp  Input Voltage: 120Vac  High Frequency Operation  Lamp Filament Preheating  Lamp Fault Protection with Auto-Restart  Low AC Line/Brownout Protection  IRS2530D DIM8TM HVIC Ballast Controller

2. Overview

The 3 way dimming system widely adopted in the US with conventional filament lamps consists of a light bulb that has a modified Edison screw type base which allows 3 connections to be made to a special lamp socket that also has 3 connections.

Standard Edison Screw

Base

Live

Neutral

Figure 2.1: Three way dimming Edison screw base

The 3 way dimming light bulb has two filaments inside which produce different light outputs when connected to the AC line. These filaments are connected in series such that the mid point goes to the line common and the two ends can be connected to the live

3 Way Dimming Edison

Screw Base

Live 1 Live 2

Neutral

www.irf.com

RD0803

- 2 -

either independently or both together. Thus with an external switch that has four positions, it is possible to obtain 3 different light levels or to switch off.

3 Way Dimming Switch

3 Way Dimming Light Bulb

Live

120V AC Line

Neutral

1 2

Figure 2.2: Three way dimming filament lamp system

3 0

1 2

40W Filament60W Filament

Figure 2.2 shows how the live and the neutral connect for 4 different configurations (position 0, 1, 2, and 3). The flow of current for each position is also shown with colored arrow; no current flows for position 0 (switch off), red arrow for position 1, blue arrow for position 2, and magenta arrow for position 3. In position 1, the current will flow through the 40W filament resistor (the lowest dimming level). In position 2, the current will flow through the 60W filament resistor (intermediate dimming level). In position 3, current will flow through both filaments, and the system will be at the maximum dimming level.

Existing Ballast Solution

There are in existence CFL ballast designs that provide three way dimming based on the same switching arrangement shown above. A common approach is a system whereby the line voltage is full wave rectified when one live input is connected and a voltage doubler circuit comes into operation when the other live input is connected or both are connected together thereby having two DC bus voltages in the ballast during dim level settings. This type of design also operates at two different frequencies, a low frequency (typically 40-45kHz) when both live inputs are connected providing a high lamp current and a higher frequency (for example 70-75kHz) when either of the two lives is connected alone which will produce a lower lamp current. In this way the following combinations are achieved:

1. Low DC bus (150V) / high frequency ….. minimum output

2. High DC bus (300V) / high frequency …... medium output

3. High DC bus (300V) / low frequency …… maximum output

This approach has some serious drawbacks:

Firstly, since the ballast must be designed to give 100% light output for the lamp when the bus voltage is 300V and the frequency is 40kHz, it is not easy to achieve satisfactory preheat and ignition when the bus voltage is at 150V because of the limitations in the peak voltage that the output circuit is able to produce from a 150Vpp half bridge voltage.

www.irf.com

RD0803

- 3 -

One strategy that has been used is to omit the preheating phase and steer the oscillator frequency to resonance during ignition using feedback from the output circuit. This ensures that at switch-on the highest possible ignition voltage will be applied to the lamp. In this way the lamp will ignite in whichever position the 3 way switch is set.

Such a scheme could reliably ignite the lamp when the DC bus is at 300V, however without correct preheating the ignition voltage of the lamp and consequently the peak current in the MOSFET half bridge during ignition will be higher. Also the life of the lamp is substantially reduced when there is no preheat due to far greater stress occurring on the cathodes at the point of ignition.

Ignition when the DC bus voltage is at 150V is very difficult. Tests indicated that sweeping the frequency down through resonance sometimes failed to produce sufficient ignition voltage leaving the ballast in open circuit running mode. The conclusion from this is that the ballast needs to oscillate at resonance for an extended period of time in order for the lamp to ignite at 150V considering that the output inductor and capacitor have been designed to produce 100% lamp power at 300VDC bus when the frequency is 40-45kHz.

Many CFL ballast designs do not incorporate a current sense and shutdown function to protect the circuit in the case of ignition failure and so the ballast would eventually fail if left switched on due to the high MOSFET switching losses causing thermal destruction. This would not matter with and integrated ballast / lamp type product when the lamp has failed.

It has also been observed that hard switching occurs at the MOSFET half bridge when the DC bus voltage is low in position 1 since when the ballast is running it will be close to resonance, bearing in mind that the resonant frequency shifts downwards in run mode. Hard switching is very undesirable because of the high peak currents that occur when each MOSFET switches on. This has been shown to result in a higher rate of field failures in ballasts due to MOSFET failure.

The conclusion is that the approach to design described above is unable to provide a reliable ballast.

The dimming level can also be controlled by simply changing the frequency. By changing the frequency between 3 defined settings, however, it was found to be extremely difficult to set a point where the dim level is 50%. The problem with this is that the lamp current against ballast frequency characteristic of the system exhibits a very sharp knee such that as the frequency increases the lamp current is gradually reduced up to a point at which a small increase of frequency will result in a very large reduction in the lamp current.

www.irf.com

RD0803

- 4 -

Ballast / Lamp Operati ng Characteristic

Lamp

Current

Ballast Running

Frequency

Figure 2.3: Lamp current against ballast frequency

To obtain 50% output, the frequency would have to be very precisely set. This is not practical since the tolerances of the output inductor, capacitor and oscillator timing components do not allow this. Even if each ballast was individually adjusted in production variations in lamp behavior over temperature would mean that under some conditions the lamp arc would extinguish at this setting leaving the system in permanent preheat which would burn out the cathodes eventually.

This explains why the 150VDC bus solution has been adopted in some designs as this allows 50% output to be achieved without this problem. However as discussed in the previous section this approach is not without some major disadvantages.

IRPLCFL4 Reference Design

It is however necessary in order to create a reliable design to include a closed loop feedback system that controls the lamp current by adjusting the ballast frequency from a VCO (voltage controlled oscillator) driven by the output of an error amplifier that senses the lamp arc current directly and compares it with a reference. This has been used in the IRPLCFL4 reference design “A 3 Way Dimming CFL Ballast” and has been demonstrated to be capable of controlling the lamp output down to approximately 10% arc current maintaining stability. This also compensates for tolerances in the components of the circuit or the lamp.

www.irf.com

RD0803

- 5 -

∑

Regulated Lamp Current Control System

VCO

DRIVER

Lamp Arc Current

Reference

Figure 2.4: Closed loop lamp arc current regulation

Many of the design issues described above have also been overcome in the ballast circuit of reference design IRPLCFL4. The design, however, required two additional operational amplifiers and additional circuitry since it is based on the IR2156 control IC, which does not incorporate the necessary dimming circuitry. This circuit therefore has a relatively high component count.

COMMON

C1 C2

D1 D2

R10

R12

IC1a

R11

R15

VCC

VDC

R16

R17

RPH

CPH

C9 C10 C11

IC1b

C20

R18

IC2

IR2156

COM

R19

C13

D10

C19

R20

C14

R21

R13

C15

C16

C12

L3a

C17

C18

L3b

R14

Figure 2.5: IRPLCFL4 Circuit Schematic

The component count for the IRPLCFL4 design shown in figure 2.5 is 56 parts.

www.irf.com

RD0803

- 6 -

New Solution: IRPLCFL8U

A completely new approach has been developed that overcomes all of the above limitations. The IRPLCFL8U reference design kit consists of a dimming Fluorescent ballast, with a 3 way dimming switch, driving a single 32W CFL lamp. The design contains an EMI filter and a dimming ballast control circuit using the

IRS2530D(

50 parts. This demo board is intended to help with the evaluation of the IRS2530D dimming ballast control IC, demonstrate PCB layout techniques and serve as an aid in the development of production ballasts using the IRS2530D.

DIM8

). The component count for the IRPLCFL8U, shown in figure 3.1, is

www.irf.com

RD0803

- 7 -

3. Circuit Schematic

SPIRAL

CFL LAMP

CH1

LRES : B

CDC

LRES:A

RLMP2

MHS

RHO

RVCC2 RVCC1

CVCC1

RS1

RS2

IRS2530D

VCC

COM

CVCC2

CRES

CSNUB

RLO

CBS

DIM

VCO

CVCO

CDIM

CH2

DCP2

MLS

RLMP1

RVCO

CCPH

RCS

LRES :C

DCP1

RFB

CFB

RDIM

RPU

PL2

PL1

C1 C2

DZ1

R5 R6

COMMON

DZ2

Figure 3.1: IRPLCFL8U Circuit Schematic

www.irf.com

RD0803

- 8 -

4. Electrical Characteristics

Parameter Units Dimming Level Value

Lamp Type 32W CFL

Maximum 31

Input Power [W]

Input Current [mArms]

Lamp Running Voltage [Vpp]

Lamp Running Current [mArms]

Start Frequency [kHz] 115

Run Frequency [kHz]

Preheat Time [s] 0.5 Input AC Voltage Range [VACrms] 60 - 180 Ballast turn-off voltage [VACrms] 60

TABLE 4.1: Ballast Parameters.

Intermediate 22

Minimum 15

Maximum 386

Intermediate 260

Minimum 175

Maximum 370

Intermediate 540

Minimum 630

Maximum 190

Intermediate 80

Minimum 27

Maximum 42

Intermediate 59

Minimum 60

5. Fault Protection Characteristics

Fault Protection Ballast Restart Operation

Brown-out Non-ZVS Increase

frequency Upper filament broken Crest Factor Over Current Deactivates Lamp exchange Lower filament broken Crest Factor Over Current Deactivates Lamp exchange

Lamp removed Crest Factor Over Current Deactivates Lamp inserted

Failure to ignite VVCOFLT+ Deactivates Lamp exchange

No lamp VLOSD- Does not

start

End of life Crest Factor Over Current Deactivates Lamp exchange

TABLE 5.1: Fault Protections Characteristics.

Line voltage

increase

Lamp inserted

www.irf.com

RD0803

- 9 -

+ 18 hidden pages