Re: simple 150uA constant current supply

On Mar 30, 3:49 pm, "Dave" <da...@xxxxxxxxxxxx> wrote:
I would like to find the simplest way to provide a constant current of
around 150uA (+/-20%) at around 2V.
Connect a voltage supply (Vin) to the emitter of an NPN transistor
through a resistor (R). Connect a reference voltage (Vref) between
the base and ground. Let Vbe be the base-emitter diode drop. Then
Iout = (Vin-Vref - Vbe)/R. The higher Vin is, the less sensitive to
Vbe the output current will be. You should use a transistor that has
a reasonably high beta at 150 uA. The alternative is to use a
Darlington transistor. The disadvantage is that now you have to base-
emitter drops to deal with.
Regards,
Jon
.

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