In article . net, "KD7TOG"
writes:

OK, here's a challenge to you guys ... I have been trying to ID a IC /
inductor combination to generate 150 to 200 VDC ... in the nano-microamp
range. I need to supply a bias voltage to an electrostatic microphone
element.

Any ideas ??

Wish list:

Very low current ... 2ma ;-)
Runs from 5 to 9 volt DC source
Minimal components

Most of the specs I find for HV units ( backlight supplies ) are too much
current. Most of the inductor type DC-DC converters seem geared towards low
voltage high current apps.

Will watch the discussion for tips and ideas ... all welcome.

A simple low-RF oscillator can do it with a small transformer having
an enormous turns ratio. I'd suggest a toroidal type with a ferrite
core rather than powdered-iron core to work around 50 to 100 KHz.
Something like a 1:30 turns ratio seems about right with the
secondary tuned, the primary driven by a single transistor emitter,
feedback to the base which will also load down the tuned secondary
some. Maybe a Darlington connection using two bipolars if too
much resistive loading.

Since a 2.5 mHy 4-pie RFC and 1000 pFd tune very close to 100 KHz,
you might use that as the "secondary." The "primary" could have
several turns wound in between the pie sections. Bulkier than a
toroid but a lot easier to handle on the first go-around for feasibility
checking. With 3900 pFd, the 2.5 mHy RFC will tune about 51 KHz.

Staying in the LF region allows most ordinary newer silicon diodes
to directly rectify the LF yet the harmonics don't interfere much with
AM radios nearby. It's well above the top frequency for human
hearing so a simple C-R-C filter ought to make the DC fairly clean
for the microphone without too much C value and bulk.

Len Anderson
retired (from regular hours) electronic engineer person