AN 066 Rev D

1 / 8

16-Jan-2004

Applications Note No. 066

Silicon Discretes

BCR402R: Light Emitting Diode (LED) Driver IC Provides

Constant LED Current Independent of Supply Voltage Variation

1. Introduction

Light-Emitting Diodes (LEDs) and LED displays

suffer from varying illumination levels as a result

of changes in power supply voltages. This is

true for displays used in automotive applications,

battery-operated handheld devices, or fixed

(architectural) installations.

To keep LED

brightness constant, it is necessary to stabilize

the LED’s current over the anticipated power

supply voltage variation range.

Often a resistor in series with the LED(s) is used

to stabilize current. However, this method has

some serious drawbacks. To achieve good LED

current stability over the varying supply voltage

range, the resistor must take on a large value

(infinite resistance, in the ideal case) to make

the

power

supply

plus

series

resistor

combination approach the traits of an ideal

constant current source having infinite output

impedance.

In such cases, there is a large

voltage drop across this series resistor. For a

particular supply voltage, this voltage drop 1)

reduces the number of LEDs that can be driven

by one resistor, requiring additional parallel

resistors with which to drive a given number of

LEDs,

thereby

increasing

system

current

consumption and 2) power is “burned” or wasted

as heat in these series resistors.

Infineon’s LED driver family, consisting of

the BCR401R, BCR402R, BCR402U and

BCR405U, offers an easy, cost-effective and

reliable way to achieve LED current stabilization

while overcoming the drawbacks inherent in

using a series resistor. These LED driver IC’s

cover the most commonly used LED supply

current ranges – 10mA, 20mA, and 50mA.

Refer to Figures 1 and 2. In each device, the

nominal drive current may be easily adjusted

upward from the nominal value by adding a

single external resistor – for BCR401R / 402R,

connect this resistor between pins 3 and 4.

Figure 1. Infineon LED Current Driver Family

Recommended Current Ranges.

Device

Package

Recommended

Current Range

Maximum

Power

Dissipation

BCR401R SOT143R 10 – 60 mA

330 mW *

BCR402R SOT143R 20 – 60 mA

330 mW *

BCR402U SC74

20 – 65 mA

500 mW **

BCR405U SC74

50 – 65 mA

500 mW **

For selecting the proper resistor value to

increase BCR402 drive current above the

nominal level of 20mA, refer to Figure 3, which