Adding AC coupling to scopes without the feature - how to measure power supply ripple on low-end scopes

138

01:08:53

My hantek 6022 USB oscilloscope doesn't have AC coupling, which makes it "impossible" to measure the output ripple of the DC-DC converters that I will be building on the breadboard (breadboarding a DC-DC converter isn't a good idea, but i can't solder 5 different circuits!). In order to measure output ripple, I need to "add" an AC coupling feature to my scope. This I will do by using the high pass filter shown above. The cutoff frequency for the above filter is 1.6KHz, so it should be fine to measure 100KHz and 150KHz ripples. If anybody has any suggestions on how to make it better, please let me know. The 10meg resistor is the input impedance of the probes.

published 6 years ago

kiani

6 years ago

Don't probes have a capacitance associated as well as 10M resistance! I think it is 22pF (not sure).. Slso you might already know, the 2K scrosd EC sVoltsge source is not doing anything cause it is oerfect source.

kiani

6 years ago

...the 1K...

PrathikP

6 years ago

Yes probes have some input capacitance as well, but I don't know the exact values so I didn't put it.

PrathikP

6 years ago

And whats 2K scrosd EC sVoltsge

kiani

6 years ago

1K across EC voltage source.

PrathikP

6 years ago

Oh that's just a random load

PrathikP

6 years ago

It wasn't really necessary

kiani

6 years ago

Just checked my old scop probe spec. The model has 1M resistsnce with a 22pF cap. Across it,. Hope that is usrful to you.

PrathikP

6 years ago

It was useful. The ripple was slightly attenuated with the new model. I should take a look at my probe's specs since the input impedance/capacitance could be different.

PrathikP

6 years ago

Yea my probe has a much higher input capacitance in 1X. It's 1meg and 85-120pF. In 10X, it's 10meg and 18.5-22.5pF.

kiani

6 years ago

Sorry the capacitance is the input capacitance if the oscilloscope,, input socket.. Need to chek scope, (is it bnc?) input sicket if oscilloscpe.. As i think the probe cap. I think the probe cap. Can be tuned out with the tiny screw on the probe, best check it out to be exact.

kiani

6 years ago

Anyway the sim doesn't need any of that.. Unless you are simulating the laborotory set up, rather than just the circuit.

PrathikP

6 years ago

Ya true

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