W
Winfield Hill
- Jan 1, 1970
- 0
Jim said:Concern for opto NPN punch thru during power-up... I could go
for a zener or some-such in there.
Silly man. No HV power supply I'm aware of has a fast enough
risetime at power-up to come close to creating such an issue.
Maybe if one was to use a HV switch in the power supply line,
but then the blame would lie in using the switch (been there,
done that, oops), not with the circuit. There is a danger if
(when) the output is instantaneously shorted, ameliorated with
a small output R.
____
V+ hv --o o-----,
+200 |
150k, 2W
| +/-170V
+---- 2.2k -------out
|
| Supertex DN2540
d depletion-mode
g ----,
s |
in--/\/\---, | 10V |
| +--|<|--+
| opto | |
a _|_ c |
_\V/_ ---> b |
k | e |
| | | ____ V-
gnd ---+-------+---o o---- -180
A higher-voltage version (+/-300V output) can be made with
a Supertex dn2470. That's a 700V depletion-mode MOSFET, the
record holder for such parts. Mouser stocks 'em.
This circuit would benefit from feedback. A Darlington NPN
would minimize the feedback-node bias current, and an offset
resistor could provide for bipolar inputs and correct for
the LED and BJT drops at the summing junction. A resistor,
say Vgs/I = 470 ohms, in the MOSFET's path would limit the
pulldown current to a few mA, to avoid overheating the FET.
V+ hv --/\/\---/\/\---, John's HV amp idea
+360 150k, 2W (2) |
| Rf/Rin = 60 +/-300V
,- Rf--+ to 1mA
Roffset | +---- 3.3k ----------- OUT
+5 ----/\/\-----+ |
Rin | | Supertex DN2470
IN ----/\/\------+ d depletion-mode
-5 to +5 | g ----,
| s |
| | 10V |
+5 --/\/-- c | +--|<|--+
b --' | |
e 470 |
| opto | |
a _|_ c |
_\V/_ ---> b |
k | e |
| | | fuse V-
gnd ---+-------+---o X o---- -320