How to make a simple constant current source

[travelerrich1]

Hey Vegmatic, thanks for the video. Looking to stabilize a current as small as 1mA for transcranial direct stimulation, or tDCS. For brain modification, decreasing or increasing the distance to threshhold for neuronal activation or deactivation. I'll be using scalp electrodes with changing resistance during a session (people move, electrolyte dries up), with a variable resistor in my voltage regulator feedback loop set at the beginning of a session. Any recommendation for a low, ~1mA current?

[ShagAsian]

@vegmatic1966 Im using a 12volt battery. Should i use voltage regulator to reduce the voltage then enter it thru the current source? Thanks for the fast reply!!!

[vegmatic1966]

@ShagAsian You will still have to dissipate the same power (in heat) across the voltage and current regulators. Voltage across the device x current through the device = watts. In this case heat that needs to be dissipated. A switching regulator is another matter and would be a better solution to the current regulation. Battery life will improve as well.

[ShagAsian]

What should I do if I want to regulate my circuit to have only about 1 to 1.5 A?

[vegmatic1966]

@ShagAsian Use an LM317 or stronger regulator.

[ShagAsian]

@vegmatic1966 i got 3A and 5A rated ones which are LM350, LD1084V, LM338T, I got them to hold at 1A to 1.5A but they overheat and shuts off. I tried to put some small sheet of aluminum in the back as heatsink but at 1.5A they are shutting off after they get too hot. is there a way to distrubute that heat more efficiently without using a fan? Thank you very much for your help and the reply!!!!

[vegmatic1966]

@ShagAsian You need a large heatsink with fins to dissipate the heat. You may have excessive voltage drop across the regulator due to your power supply. Try to measure the voltage across the IC (input to output) before it shuts down. If it is more than 5 or 6 volts, try to reduce your supply voltage so the regulator will produce less heat.

[dzcovel]

Thanks for the video!

[ruser0084]

So is this a just a clever and simple use of feedback? Cool, I like it What happens at infinite load (open circuit ) on the current source output? Does the voltage regulator have some sort of high voltage protection and if so how high does the voltage rise?

[SirArghPirate]

Informative. Thanks.

[Forssa1]

It's 1.25V, not 1.2V.

[Wizard4592]

hehe, your test bench looks just like mine

[paliver]

... and a heat sink ... (or at least a fire extinguisher)