Re: simple 150uA constant current supply

On Apr 4, 9:27 pm, "Paul E. Schoen" <pst...@xxxxxxxxx> wrote:
"James Arthur" <dagmargoodb...@xxxxxxxxx> wrote in message

news:ae891525-8234-4422-88f4-80908a2c19b4@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx



On Apr 4, 2:26 pm, "Paul E. Schoen" <pst...@xxxxxxxxx> wrote:

I made a self-referential circuit using a 2N3904 and 2N3906. It works in
the SwitcherCad simulator down to 2.1 volts. It may not be very stable
with
temperature, but it's cheap and easy.

Paul

[snip SWCIII ckt]

For improved temp. stability just compensate Q2's Vbe:

Vcc
-+-
|
+------------.
| |
[D2] [1.5k]
| |
[68k] +---.
| |<' |
+---------| [4.7M]
| Q2 |\ |
| +----'
| |
\| Q1 |
|---------+
.<| |
| [LED]
[150k] |
| ===
===

(D2 added, resistor values adjusted.)

Try it and compare![*]

[*] In SWCIII, .STEP TEMP 0 50 10

Cheers,
James Arthur

That is much better, about 0.48%/Degree C. I didn't know about the .STEP
directive. This info may come in handy.

I think the OP has left the
building, but I have gained useful information.

OP? Runnt oft by the ruckus, I 'spect. But we can still have fun,
can't we?

Cheers,
James Arthur
.

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