Vicor Constant Current Demonstration Board User Manual

USER GUIDE | UG:007

Constant Current (CC) Demonstration Board

The Constant Current (CC) Demonstration Board described in this document shows how to use a

Contents Page

Introduction 1

PRM regulator as a constant current source. The CC demonstration board is not designed for
installation in end-user equipment. The system demonstrates the use of a PRM
drive light-emitting diodes (LEDs) or for general laboratory evaluation.

®

and a VTM®to

Features 2

General 3-7

Test Procedure 8-15

Bill of Material 16

Ordering Info 17
Summary

Please read this document before setting up a customer demonstration board.

The User’s Guide is not comprehensive and is not a substitute for common sense and good
practice. For example:

1. When testing electronic products always use approved safety glasses.

2. Provide a strain relief for wires and place the system on the bench in such a way as to prevent
accidental dislodgment from the bench top.

3. Remove power and use caution when connecting and disconnecting test probes and interface
lines to avoid inadvertent short circuits and contact with hot surfaces.

4. Never use a jumper in place of the fuse. Replace the fuse only with its equivalent type and rating.

5. Never attempt to disconnect the CC demonstration board from a VTM customer board while
power is applied. This system is not designed to demonstrate hot plug capability. Additional
components would be required to implement a hot plug capable system.

1.0 Introduction

The PRM Regulator can be set to either regulate its output in a Local Loop mode or regulate the
output of a VTM Voltage Transformer at the point of load in an Adaptive Loop. Adaptive Loop
regulation is realized through the addition of a compensation resistor to the CD pin. Please refer
to the

Factorized Power Architecture (FPA™) white paper for more details. The CC demonstration

board is designed to provide a precise regulated current. This is particularly useful in LED driving
applications where the intensity and brightness are controlled by regulating the current through
the LED.

The VI Chip solution provides an efficient, power dense means of powering high current opto­semiconductor LEDs such as Enfis products UNO and Quattro arrays as well as OSRAM product
OSTAR.

The P048F048T24AL-CC board may be used to provide up to 5 A when employed as a standalone
non-isolated source. A PRM–VTM combination provides isolated current multiplication up to 100
A. Separate VTM boards allow customers to choose a desired output current and voltage range.
To obtain a VTM customer board, simply add “-CB to the VTM part number.

UG:007 vicorpower.com Applications Engineering: 800 927.9474 Page 1

2.0 Features

+IN

J01

+

–

+

–

–IN

–OUT

+

OUT

R33

J02

TP08

TP06

TP04

TP05

TP07

TP02

TP01

TP03

S

W01

F01

C4

C1

C2 C3

R3

VH

C

12

L01

R28

R27

R8

R32

R30 R23

R12

R13R18

R

17

R16

R19

VH

C11

U02A

U02B

R21

R24

VSENSE

VREF V

H

SW02

R10

SLC7530

PS01

V

C

PC

TM

IL

NC1

P

R

+IN

–IN

V

H

SC

SG

OS

NC2

C

D

+

OUT

–OUT

R6

CONN - 10 PIN - MALE

The CC Demonstration Board contains the following:

1. High power density PRM.

2. Adjustable current output of up to 5 A (if no VTM is used).

• Adjustable current output of up to 100 A with the use of a VTM customer board.

3. Adjustable PRM maximum output voltage.

4. Kelvin connections for measuring the efficiency of the VI Chip components independent
of load connect losses.

5. Oscilloscope probe jacks for measuring output voltage, including output voltage ripple.

6. Fused PRM input.

7. Provision for mounting optional VI Chip pushpin heat sink.

8. System enable and disable.

CC Demonstration

Figure 1

Board Schematic

Figure 2

CC Demonstration

Board

Double click the image to see a larger view.

2.1 CC Demonstration Board Description

UG:007 vicorpower.com Applications Engineering: 800 927.9474 Page 2

2.1.1 General

C01

C02

C03

J01

C6

R

15

C7
R16
R17
R18
R19
C9

C8

R11
R12
R13
R14

C5
R

6

R7

R20

R21

R4

R5

U01

U02

T

P6

TP2

TP3

TP1

TP4

T

P5

T

P7

TP8

L01

R33

R32

J02

R30

C14

C15

R31

R24

R25

R26

C11

R27

R22

R23

R28

C12

C13
R29

C10

R10

R8

R9

SW02

Q

01

F01

C4
R

1

R2
R3

SWO1

PS01

D01

1. Source voltage DC input points (+IN, –IN): Designed to accommodate #10 hardware and
Panduit ring lugs. The PRM has no reverse power protection so be sure to observe correct
polarity.

2. Toggling switch (SW01): Used to enable or disable the PRM. The ON position enables the

RM by allowing the PRM PC pin to float. The OFF position disables the PRM by pulling

P
the PRM PC to signal ground (SG).

3. Toggling switch (SW02): Used to open or close the connection between the reference
voltage produced from the potentiometer (R10) and the positive input of the comparator
op amp. This is provided as an added feature to allow the use of an external shunt
regulator. The recommended component is TLV431B. For further details refer to application
note

AN: 018 Providing a Constant Current for Powering LEDs using the PRM and VTM

Make sure to turn this switch to the "open" position when a shunt regulator is in use.

4. Output voltage points (+OUT, –OUT).

5. Output connector (J01): Used for mating with VTM-CB providing V
dedicated to the +OUT, four for the –OUT, and two for the VC. Each contact is rated for
3 A. The excess capacity afforded by these pins can facilitate testing multiple VTM-CBs
from a single PRM-CC using appropriate wiring harness and mating connector. This may
also be achieved using the large pads of the output voltage points.

and VC. As shown

OUT

CC Demonstration

Figure 3

Board Layout

Double click the image to see a larger view.

UG:007 vicorpower.com Applications Engineering: 800 927.9474 Page 3

2.1.2 CC Demonstration Board Components

+Out

–Out

+In

–In

VC
PC
TM
IL

VH

PR

NC

SG

SC

PRM -AL

OS
NC
CD

Vout

Vin

1. Input capacitors (C01, C02, C03): A 22 µF capacitance assuming a low input source
impedance.

2. Fast-acting fuse (F01): Rated for 10 A.

3. Potentiometer V

(R10): Provides an adjustable voltage divider in combination with (R6).

REF

This divider achieves the reference voltage used to set the value of the PRM output
current. Please refer to the application note

AN: 018 Providing a Constant Current for

Powering LEDs using the PRM and VTM for more details on start up sequencing precautions.

4. Potentiometer V
to in the

PRM datasheet. The OS resistor is used to set the output voltage of the PRM.

(R8): Combined with (R27) V

MAX

make up the OS resistor referred

MAX

In this case it is used to limit the PRM maximum output voltage the CC feedback can drive
in order to source more current.

5. Dual op amp (U02): U02A shown in Figure 1 is used as a difference amplifier sensing the
voltage produced by the current flowing though the PRM output sense resistor (R33).
Op amp (U02B) regulates the output of op amp (U02A) against the manually set reference
using the potentiometer (R10) or an external shunt regulator.

6. Output inductor (L01): The PRM soft switches at a frequency greater than 1 MHz while the
VTM soft switches at a frequency of 1.7 MHz. L01 is used to reduce the high frequency
current ripple produced by the high frequency switching inside the PRM.

7. Sense resistor (R33): The voltage across the sense resistor is captured by the difference
amplifier then fed back to the PRM SC pin through the error amplifier in order to maintain
the current regulation. R33 is a 1 w, ±0.1% tolerance, 10 mΩ high precision metal strip
current sense resistor positioned at the –OUT of the PRM.

8. PRM connection highlights:

PRM-AL Schematic Symbol

Figure 4

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A. Auxiliary voltage (VH): The op amp is powered using the VH pin. This pin is a 9 V ±0.3 V

regulated voltage capable of sourcing up to 5 mA. Do not exceed the current rating
for VH. Exceeding the current limit will render the unit inoperative. To increase VH
capability an external circuit scheme using a power transistor can be used as described in
application note

AN: 018 Providing a Constant Current for Powering LEDs using the PRM

and VTM.

B. Secondary control (SC): The output of the comparator op amp (U02B) is connected to the

SC pin. This pin will be driven high to drive the PRM output voltage high and vice versa.
The resistor divider formed by (R23 & R30) controls the maximum voltage at the input of
this SC pin. The output of the comparator is about 9 V. Care must be taken when selecting
values different than the recommended (R23 & R30). Please refer to the application note

AN: 018 Providing a Constant Current for Powering LEDs using the PRM and VTM.

C. Output set resistor (R27): This pin defines the maximum output voltage of the PRM when

the error amplifier output drives the SC pin to its maximum. The combination of both
resistors (R27 & R8) forms the R
R

resistor by turning the potentiometer (R8) clockwise will increase the maximum

OS

resistor required to operate the PRM. Reducing the

OS

output voltage. The Fixed resistor (R27) value is chosen to ensure a maximum output
voltage of 55 V. Please refer to the
how to choose the appropriate R

PRM P048F048T24AL datasheet for more details on

value for the desired PRM maximum output voltage.

O

S

D. VTM control pin (VC): This PRM output pin provides a 10 ms pulse during start up enabling

the downstream VTM. VC is connected to pin (3 & 4) on (J01) connector.

2.1.3 Test Points

1. Input & output Kelvin test points –IN, +IN (TP1 & TP3) and –OUT, +OUT (TP7 & TP8):
These input/output access points of the PRM enable accurate efficiency measurements of
the VI Chip independent of the interconnection losses.

2. PC (TP3): Test point primary control signal. During normal operation this pin is internally
pulled high to 5 V. Drive this pin low by moving (SW01) to the OFF position to disable the
PRM output. This pin will pulsate under fault conditions.

3. V

(TP4): Test point voltage sense serves to show the output voltage of the difference

SENSE

amplifier (U02A). This voltage is proportional to the actual PRM-sensed output current.
The constant of proportionality is equal to the difference amplifier gain formed by the
resistors (R16-R18). If the recommended gain of 100 is used in combination with the
10 mΩ sense resistor the outcome is a one-to-one relationship between the measured
voltage at this test point and the PRM output current. (V

4. V

(TP5): Test point voltage reference value is being compared with the sensed voltage

REF

V

. Op amp B is providing an output voltage to the SC pin in order to retain V

SENSE

V

REF

= I

OUT_ PRM

assuming that R

x Gain = 1. Turn the potentiometer (R10)

SENSE

SENSE

= R

SENCE

x Gain x I

OUT_ PRM

SENSE

clockwise to increase the required output current set point.

5. SG (TP6): Test point signal ground is the ground reference for the internal control IC.

6. Output voltage oscilloscope probe jack (J02): Accepts most oscilloscope probes and
enables precision measurement of the output voltage ripple.

)

=

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2.2 Mounting a Heat Sink

Typical Heat Sink

Figure 5

A pushpin VI Chip heat sink is included with the CC demonstration board to allow extended

bench top testing at full power and lower airflow.

The PRM is equipped with an over-temperature shut down feature. Please refer to the data
sheet for more details.

2.3 No Load Connection

The CC demonstration board relies on the feedback provided by the current flowing through
the sense resistor (R33). If no load is connected to the module output the CC loop will detect a
no-current flow and will steer the SC pin accordingly to the maximum value. The output
voltage of the PRM will be driven to its highest set point. The resistor (R27) can prevent the
PRM from going into an output over-voltage fault during this condition by limiting the
maximum PRM output voltage. The PRM is equipped with over-voltage protection. However, if
the circuit drives the PRM into over-voltage with no load, the PRM may be damaged. Please
refer to the appropriate section for guidelines on properly setting the maximum PRM output
voltage.

2.4 VTM Shut Down

The PRM initiates a VC pulse at start up for the downstream VTM. The VC pulse is used to
synchronize the output of the VTM with the PRM output voltage. If the PRM detects a fault
condition, it will initiate the 12 V, 10 ms pulse to the downstream VTM. Adjusting the (R10)
counterclockwise to limit the output current will drive the PRM output voltage low. It is
possible to manually trigger the under-voltage mechanism where the PRM goes into fault
condition as shown in Figure 6.

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