Winfield Hill wrote...
[email protected] wrote...
I think you want a linear high-voltage opamp, such as those
made by Apex, powered from a small 150V dc-dc switching power
supply. Setup the opamp for a gain of 10x. Yawn.
I didn't notice you were going to make 100 of these, powered from a
single power supply. The APEX amplifiers are easy to use, but they
are expensive. I still think a linear solution bests a switching
supply solution, but with 100 units something simple and cheap is in
order. I suggest you use a circuit like fig 3.75 in our book, except
with transistors instead of FETs. Here's one that should work well:
.. ---+-------+-- 130 to 150V HV supply
.. | | 100 amplifiers requires
.. R4 10k R5 70mA maximum (all at 0V)
.. Simple, Cheap 220k |
.. Precision Slow | |/ Q2
.. HV Amplifier +-----| mpsA42
.. | |\v
.. G = 1 + R2/R1 | | R3
.. +--|<|--+--+--- 2.2k ---- out
.. | 1n4148 | 0 to 110V
.. |/ | +/- 4mA
.. gnd --| mpsA42 |
.. |\v Q1 |
.. 0-10V __quad opamp | |
.. in -----|+ \ R6 | R2
.. | >--+-- 3.3k --' 1.00M 1%
.. ,--|-_/ | |
.. | === 330pF |
.. | | C1 |
.. '---------+---------------------+
.. | R1
.. +/-15v opamp supply 100k 1%
.. |
.. gnd
I've used a common-base non-inverting high-voltage stage to allow
simple one-cap C1 feedback-loop compensation. R5 and R6 provide
short-circuit limiting. R3 isolates the feedback loop from large
capacitive loads, but can be eliminated if you increase C1. Note,
the mpsA42 transistors can handle 300 volts, so the output range
could easily be increased.
You haven't mentioned the accuracy or speed you need. If these are
very relaxed specs, you can eliminate the opamp and drive the level-
shifting stage directly from your D-A stage, using the -10 to 0V
part of your D-A range. Although a regulated HV supply is required,
this is a dramatically simplified circuit!
.. ---+-------+------- Vcc = 120V
.. | | regulated HV supply
.. R4 27k R5 60mA max for 100 amps
.. 200k 1% |
.. Super Simple | |/ Q2
.. no-feedback +-----| mpsA42
.. HV Amplifier | |\v
.. | |
.. +--|<|--+---+------ out
.. | 1n4148 | 0 to 110V
.. |/ 220k +/- 1mA
.. gnd --| mpsA42 |
.. |\v Q1 gnd
.. |
.. R6 | R4
.. -10 to 0V in --- 12.0k --' Vout = Vcc - -- (-Vin - 0.65V) - 0.65V
.. 1% R6
There's a slight nonlinearity, especially near the maximum output
voltage, where the D-A converter signal approaches Q1's 0.65V Vbe.
But you could easily calibrate it out, because it'll be the same
for all 100 amps and it won't change much at room temperature. If
the 1st 0.65V term in the equation is too much of a pain, you could
create a +0.65V point and tie all 100 Q1 bases to that.
Or you can add 25 quad opamps to eliminate the Q1 offsets:
.. ---+-------+------- Vcc = 120V +/-0.5V
.. | | regulated HV supply
.. R4 27k R5 60mA max for 100 amps
.. 200k 1% |
.. Simple 2% Precise | |/ Q2
.. HV Amplifier +-----| mpsA42
.. | |\v
.. | |
.. 1/4 LM324 +--|<|--+---+------ out
.. __ | 1n4148 | 0 to 110V
.. gnd ----|+ \ |/ 220k +/- 1mA
.. | >-----| mpsA42 |
.. ,--|-_/ |\v Q1 gnd
.. | |
.. '--------------+
.. R6 | R4
.. -10 to 0V in --- 15.0k --' Vout = Vcc - -- ( -Vin ) - 0.65V
.. 1% R6
The last 0.65V term comes from the Vbe drop of Q2. There's still
a small missing contribution to the output equation coming from
Q1's base current, but that should be under 1% for typical parts.
If that concerns you, make Q1 a Darlington with two mpsA42 parts.
I think if you add it all up, this'll beat 100 switching circuits.
