BCR402 Infineon Technologies Corporation, BCR402 Datasheet - Page 5

• Manufacturer Part Number: BCR402
• Description: Light Emitting Diode ( Led ) Driver ic Provides Constant Led Current Independent of Supply Voltage Variation
• Manufacturer: Infineon Technologies Corporation

When used in this way, the BCR402R acts as a
“current sink” for the diodes D
top stack of LEDs, and as a “current source” for
the diodes below, e.g. D
there is only one current path, stabilization is
maintained for both upper and lower stacks of
LEDs. There is a vanishingly small difference or
“error” in terms of the current difference between
LEDs in the top stack and the bottom stack, this
difference being created by the base current
consumed by the internal PNP transistor in the
BCR402R. This base current, and therefore the
current difference between top and bottom LED
stacks, is only about 400 microamps at a
nominal 20mA LED current.
human eye will not be able to discern any
differences in brightness in LEDs between top
AN 066 Rev D
(High = ON)
ON / OFF
Control
D
Use enough LEDs in
"top LED stack" such
that voltage at pin 3 of
BCR402R is < 18V
1
, D
2
, ..., D
R2
1K
Figure 7.
N
Q1
:
N+1
1
4
, D
W6s
+V
R1
1
S
N+2
Operation of BCR402R at “High” Voltages e.g. > 18V.
, D
, …, D
3
2
2
As such, the
, …, D
D
D
D1
D2
D
D
N+X
BCR402R
N+1
N+2
N
N+X
N
on the
.
D
Use maximum number of
LEDs in "bottom stack" that
permits sufficient voltage
between pin 2 and ground to
drive them.
N+1
As
, D
N+2
Note: maximum possible number of LEDs that can be used in
entire circuit depends upon +V
diode types. Q1 and R2 are optional, if it is desired to switch LED
stack on and off at this point. If switch is not needed, ground pin
1 of BCR402R. Be sure Q1 can handle voltage present at pin 1
of BCR402R given the value of +V
a broad range of switching transistors suitable for Q1.
5 / 8
, ..., D
and bottom stacks due to this effect. In fact,
there is far more variation in brightness between
individual LEDs of the same type, if they are all
driven with identical currents, than could be
attributed to this small “error” current due to the
BCR402R’s PNP transistor base current.
In closing, for either the high voltage application,
or standard application, an external NPN
transistor (Q1) may be used as an ON / OFF
switch for the LED circuit, if desired. Infineon
Technologies
switching transistors suitable for this purpose,
and the best choice will depend on the voltage
present at pin 1 of the BCR402R, e.g. select a
switching transistor with sufficient collector-
emitter and collector-base breakdown voltages.
N+X
:
Applications Note No. 066
markets
S
& voltage drop across particular
S
selected. Infineon produces
a
broad
Silicon Discretes
16-Jan-2004
range
of