Author Topic: High Voltage DC Blocking  (Read 660 times)

0 Members and 1 Guest are viewing this topic.

Offline nicknails

  • Contributor
  • Posts: 40
High Voltage DC Blocking
« on: October 11, 2017, 02:46:25 am »
I have a need to measure AC ripple on the output of high voltage DC converters (anything in the range of 1kV-20kV). My thought is to filter the DC with multiple caps, then use an op-amp to amplify the ripple to make it easier to measure on a scope. All I have is a TDS1002B that goes down to 20mV/div. On the lower voltage stuff the ripple is in the 20-40mV range and nearly impossible to see on the scope. My current setup is a 0.01uF in series with a 10M and measure across the resistor. This works but there's a transient spike on the cap. My understanding is that if I put multiple caps in series, the transient spike will be smaller and smaller on successive caps, but I have no idea how to calculate the capacitance or how many caps are needed. The ripple frequency is anywhere from 60k-300kHz.

I'm assuming I'll need separate setups because of the voltage range, which isn't a problem. I have some nice AD822 op-amps that I'll be using, which can run up to +/-15V, so I'm thinking I can get the ripple in the 4-8V range.

Please no rants about high voltage and killing myself   :blah::blah:. I've been doing HV DC/DC converters for many years (up to 12kV), just never had a need to measure such a small ripple.
 

Offline ebclr

  • Super Contributor
  • ***
  • Posts: 1750
  • Country: 00
Re: High Voltage DC Blocking
« Reply #1 on: October 11, 2017, 02:58:01 am »
Why not use a high voltage probe ?




 

Offline ovnr

  • Frequent Contributor
  • **
  • Posts: 658
  • Country: no
  • Lurker
Re: High Voltage DC Blocking
« Reply #2 on: October 11, 2017, 03:03:04 am »
Transient during capacitor charging: Just clamp it with a TVS or Zener or something to that effect - you've already current-limited it with the series resistor (beware maximum working voltage, etc).
 

Offline nicknails

  • Contributor
  • Posts: 40
Re: High Voltage DC Blocking
« Reply #3 on: October 12, 2017, 12:03:47 am »
Why not use a high voltage probe ?


This would require the scope to be set to 1000X, making it 2V/div minimum.


Transient during capacitor charging: Just clamp it with a TVS or Zener or something to that effect - you've already current-limited it with the series resistor (beware maximum working voltage, etc).

I have no experience with TVS diodes; I'll do some research and check that option out. Thanks.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf