Photoflash units typically keep oscillating and drawing power even
when the cap is charged, but if you arrange to turn one really OFF
most of the time, the average current could be very low. You just
need a cap that will hold the charge well. Polypropylenes are known
to do a very good job in that respect, but in any event the reverse
leakage of the rectifier diode is likely to dominate. It's possible
to come up with ridiculously low reverse leakage rectifiers if it's an
issue.

Because of the low current required, it's worth thinking about using a
voltage multiplier. A simple blocking oscillator (transformer and
transistor) with even just 5:1 stepup to the secondary, then some
voltage multiplication, should do it.

You didn't mention regulation: the mic sensitivity will generally be
proportional to the bias voltage, so some regulation is probably
appropriate.

Another possibility: a stack of 60 or so lithium coin cells. Quiet,
good voltage stability, ten year life. At about 40 cents each from
DigiKey, the $25 cost is probably less than you do an 'lectronic
solution if your time is worth anything. Can be packaged into a
cylinder about an inch in diameter and four inches long. (PVC pipe +
fittings + small spring?) Completely isolated: no possible ground
loops. No oscillator to generate noise.

Cheers,
Tom


"KD7TOG" wrote in message link.net...
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.

Thanks

Tony, KD7TOG

( KD7TOG at earthlink dot net )