Op Amp Driven HV meters
Op Amp Driven HV meters
(OP)
I am in the process of building a High Voltage power supply for a CO2 laser, it's 15KV current limited @ 30ma. I need a circuit that will monitor the voltage and current of the output across the discharge tube. Remember this circuit must handle HV without letting the magic smoke out of the chips.
The finished circuit will be incased in an oil filled unit for safety.
The finished circuit will be incased in an oil filled unit for safety.





RE: Op Amp Driven HV meters
TTFN
RE: Op Amp Driven HV meters
RE: Op Amp Driven HV meters
For current measurements, you could try a magamp circuit (aka Kraemer transducer or current transductor). Or use a low current LEM transducer. You will need to use a primary winding with several turns to get a decent resolution.
If you can put a sensing resistor in the current path near ground potential, it will be a simple matter to just measure tha voltage drop across it.
RE: Op Amp Driven HV meters
The current measurement could be done using torroids, resistors, or even a little IC chip (where the current to be monitored is passed under the chip via a trace on a PCB). I would opt for the torroid or a little hall effect chip (if you are using a PCB) simply because of the isolation provided.
In addition, if a transformer is used for voltage measurements you will also be isolated.
They do make resistors designed specifically for current measurements (better temp coefficient and tolerance).
RE: Op Amp Driven HV meters
It sounds as though you are looking at unusual solutions to normal straightforward problems.
High voltage measurements are usually done with resistive dividers. It is true that direct measurements are possible with spark gaps, but for your application a resistive divider is the correct solution. If it is too noisy then that problem needs to be fixed. Is it some high frequency signal getting onto the high impedance attenuator? If so, then put a capacitor across the output of the divider and/or put an electrostatic shield around the divider. If you are creating the EHT from an unshielded EHT transformer then put an electrostatic shield around the transformer to minimise the stray capacitive couplings.
If you are looking at the DC value of the EHT supply then all those transformer proposals are obviously inappropriate.
Skogs is right about measuring the current in the low potential part of the circuit, ie in the ground return conductor. This trick makes the measurement much easier.
RE: Op Amp Driven HV meters
RE: Op Amp Driven HV meters
These probes also work into an oscilloscope, and I have never become aware of any serious HF noise problem when doing so.
RE: Op Amp Driven HV meters
We used to have a small heated vessel with transformer oil and everything that was supposed to be used under oil was tested there for at least half a year ( and lots of components failed !).
RE: Op Amp Driven HV meters
I am trying to have the highest impedance possible, I found a circuit online that uses an 80M and 82K divider circuit as the starting point of the OP-AMP driven meter movement. I am just leery about running 15KV @ 30MA directly through a shunted meter movement in a metal case. If it’s what I need to do, so be it. Let me know.
RE: Op Amp Driven HV meters
I dont understand why the voltage measurement before the HV transformer is not adequate. This number could factor in the transformer ratio to come up with the secondary voltage (HV). This is typically how HV measurements are done.