BCR402U_09 Datasheet, PDF (7/9 Pages) Infineon Technologies AG – LED Driver

Application circuit:
Stand alone current source
BCR 402U
+Vs
4
Rext
(optional)
6
Vdrop
BCR402U
Application circuit:
Boost mode current source with
external power transistor
BCR 402U
+Vs
4
Rext
(optional)
6
Vdrop
I_LED
1
2,3,5
Is
Iout
1
2,3,5
Is
Iout R1
R2
Application hints
BCR402U serves as an easy to use constant current source for LEDs. In stand alone
application an external resistor can be connected to adjust the current from 20 mA to 65 mA.
Rext can be determined by using the diagram 'Output current versus external resistor',
or by refering to diagram 'Reference voltage versus output current'. Look for your desired
output current on the x axis and read out the corresponding Vdrop. Calculate Rext:
Rext = Vdrop / (Iout -(Vdrop/Rint))
Please take into account that the resulting output currents will be slightly lower due to the
self heating of the component and the negative thermal coefficient.
In boost mode configuration the LED current can be extended to drive high power LEDs.
Select the power trasistor according the power dissipation and output current requirements.
(e.g. BC817SU or BCX68-25, etc.) Dimension R2 to reduce the transistor current transfer
ratio to 20 ... 50. For ILED / Iout =50 e.g. ILED= 350 mA, Iout is 7 mA.
R2 = VbeON / Iout.
Dimension R1 for minimum supply voltage condition:
R1 = (Vsmin -1.4V -VbeON)/ Iout.
Please visit our web site for application notes: www.infineon.com/lowcostleddriver
• AN077 gives hints to thermal design
• AN097 helps in case of high supply voltages
• AN101 gives an overview to LED biasing
7
2009-07-31