Multi (wide) Voltage LED using LM317

Question

Just a thought, we know you can change a linear voltage regulator like the LM317 into a series constant current regulator by just adding one resistor (loads of application notes on Farnell Web site) but can it be done with the LM431 adjustable shunt regulator?

Anyone know?

Regs (regards not regulator)

Malcolm

samplerman · Answer

HI The LM341 could be used, but on its own it can only sink 100mA so it may be better to stay with a resistor. If however the device is used with a series pass transistor then higher currents may be passed. The most efficient approach though would be to use a switching regulator chip as 85 to 90% efficiencies can be acheived.

Former Member · Answer

, This above picture is the typical application circuit of LM431, it shows us how to adjust VKA. If we replace R1 with LEDs, LEDs current will be adjusted by R2 and Vref. If Vref and R2 is constant, LEDs current will be constant too