Author Topic: How to measure HV DC power supply ripple voltage?  (Read 266 times)

0 Members and 1 Guest are viewing this topic.

Offline 001

  • Regular Contributor
  • *
  • Posts: 208
  • Country: 00
How to measure HV DC power supply ripple voltage?
« on: December 05, 2017, 02:24:41 AM »
Power Supply rated as 480volts 180mA DC
Ripple voltage (saw waveform) range about tens millivolts
How to measure ripple voltage and not destroy any gear? :-//
« Last Edit: December 05, 2017, 02:48:54 AM by 001 »
 

Offline e61_phil

  • Frequent Contributor
  • **
  • Posts: 438
  • Country: de
Re: How to measure HV power supply ripple voltage?
« Reply #1 on: December 05, 2017, 02:32:03 AM »
With AC-coupling.

Be careful, most scopes have a DC high-impedance if you switch them to AC-coupling. In this case, the scope will see the full DC voltage even if you use a 1:100 probe.

I've build an AC-coupler to measure noise on voltages of up to 10kV. The design is very simple: In front is a coupling capacitor followed by a 9Meg resistor. A variable capacitor is used to trimm the capacities. This gives a flat frequency response from below 1Hz to 10MHz, which is way more than I needed.
« Last Edit: December 05, 2017, 06:10:26 AM by e61_phil »
 
The following users thanked this post: 001

Offline David Hess

  • Super Contributor
  • ***
  • Posts: 5490
  • Country: us
  • DavidH
Re: How to measure HV power supply ripple voltage?
« Reply #2 on: December 05, 2017, 06:07:26 AM »
Be careful, most scopes has a DC high-impedance if you switch them to AC-coupling. In this case, the scope will see the full DC voltage even if you use a 1:100 probe.

They are rare now but good x100 probes include an internal shunt preventing this problem.  They can be identified by having a specified input resistance which is less than 100 megohms.  A good example is the old Tektronix P6009 x100 probe which has a 10 megohm input resistance.

But a standard dividing probe is the wrong way to make this measurement.  Do what e61_phil suggests and make an external high voltage DC block with the needed frequency response.
« Last Edit: December 05, 2017, 12:54:59 PM by David Hess »
 

Online eliocor

  • Supporter
  • ****
  • Posts: 285
  • Country: it
    • rhodiatoce
Re: How to measure HV DC power supply ripple voltage?
« Reply #3 on: December 05, 2017, 11:07:14 AM »
take a look at AN-118 from Linear Technology: http://www.linear.com/designtools/app_notes.php
Please READ IT ALL !!!
 
The following users thanked this post: 001


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf