Adjustable Constant Current Drive

Is the load floating or grounded? What resistance/ impedance are you driving? What frequency response do you need?

Paul Burke

Its for driving an experimental LED. Not really concerned with frequency response. As long as I can get 250mA(which can be adjusted, so I can check a range of drive currents) in there from that supply voltage and not use any expensive components I'll be happy.

Thanks

Graeme

Look at the NS LM10. Pretty should work just fine and you will not even need the negative supply. Gives you a 200mV Vref and an op amp, to use as an error amp, all in an 8 pin DIP.

Jim

You can use an LM317 voltage regulator as a variable current source. Details are in the data sheet. Another technique is to vary the voltage to the base of an NPN BJT with the LED between the collector and the positive supply. This will provide a constant current to the LED, depending on the base voltage.

Leon

As Leon mentions, maybe this kind of arrangement ...

o-------------------o-------5V | | .-. .-. | | | |4.7 ohm | | | | '-'150 ohm '-' | | | | PNP Darlington .-. |< TIP ??? | |