I've built one for ~ $30 in parts from Radio Shack using an LM317 current limiter.
But the data sheet for the LM317 says the minimum operating current is 2.0 mA, yet the amount delivered to the brain should be 1 mA. How did it work?
But the data sheet for the LM317 says the minimum operating current is 2.0 mA, yet the amount delivered to the brain should be 1 mA. How did it work?
From the datasheet
>all quiescent operating current is returned to the output terminal. This imposes the requirement for a minimum load current. If the load current is less than this minimum, the output voltage will rise.
I've used an LM317 drawing less than 2mA, so I assumed it was possible (in hindsight I must have used the solution, below).
The solution is very simple however, make a separate parallel circuit that will draw at least 2mA. This can be accomplished just by placing a resistor of appropriate value between the Vout and ground.
different types (small,large case) of LM317 havemaybe different parametrs