Re: simple 150uA constant current supply

On Sun, 30 Mar 2008 20:50:12 -0400, Fred Bloggs <nospam@xxxxxxxxxx>
wrote:


Thanks Martin but, it's not homework, I don't have any space for an
IC and this is battery powered. I can only spare about 30uA to
'generate' this supply.

There are microscopic nanopower opamps from Linear and others. Since all
you want is nominal +/-20% , and this is the same as Vbatt ranging from
2-3V, then something simple that does not require much battery current
would be like so, total bias around 16ua, compliance should be to within
a few hundred millivolts of the rail, and you could do even better with
a PFET:
View in a fixed-width font such as Courier.

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. BATT---+-----------+-----------.
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. [3.9k] | [390]
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. | .----|-----------+
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. | '-|-\| |<
. | | >---------| 2N3904
. +--------|+/| |\
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. | | Iout
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. [166k] |
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. COM---+-----------+-------
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That circuit will usually oscillate, sometimes at two different
frequencies simultaneously.

John

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