Measuring very low ripples on a high voltage multi-kV output

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SiCEngineer

Joined May 22, 2019
238
Hi,

I am designing a switched mode power supply for a travelling wave tube. In this research my ripple has to be approximately 10mV on a 6kV output. What is the best way to measure this voltage ripple at such low levels? My voltage divider is a 1/2000 ratio, meaning that a 10mV ripple on this will be translated to approx. 10mV/2000 value. The only ways I have came across so far is using a capacitvely coupled op-amp to remove the DC offset (high pass filter) and then amplify the output signal with the op-amp by say again the 2000 ratio so that it is replicated at the output of the op-amp. But is 10mV still too low to detect accurately? Are there any more efficient, accurate ways to perform this measurement?
 

ronsimpson

Joined Oct 7, 2019
932
First the 10mV specification is very small. I think 10V of ripple is fine, but I don't know much.
Use a capacitor + resistor to remove the DC from the reading and pass the AC to the meter/scope. Like you said "high pass filter". You should put some protection across the resistor. Maybe to back to back Zener diodes to keep high voltage off you meter/scope or amplifier. At power up and power down the voltage on the resistor can get very large.

I use a scope because I can see 10mV. You may have a problem measuring 10mV near a switching power supply because of noise.
 
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