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Agent_24
10-10-2007, 09:38 AM
Is there a way I can test PC PSU output ripple without an oscilloscope?

Found this, http://www1.jaycar.co.nz/productView.asp?ID=KA1811 but looks like it would only work for audio?

Agent_24
11-10-2007, 10:20 AM
I found this, also http://www.geocities.com/lptscope/

Reckon it would be any good?

dugimodo
11-10-2007, 10:39 AM
you could probably use that kit and just stick a resistor in series to drop the voltage down to safe levels, it wont affect the ripple significantly.

A proper oscilloscope would be better of course. You could also just try an analogue volt meter and see how steady the needle is, although that's pretty crude and would only show up slow fluctuations reliably.

linw
11-10-2007, 11:24 AM
I have used a software scope for checking my radio control transmitter waveforms that were fed into the line-in socket. Worked great. The Jaycar circuit looks good as it would isolate the input while providing amplification if necessary. (The isolation bit is good as I fried the sound card input on my mobo by being careless!).

Billy T
11-10-2007, 06:30 PM
Is there a way I can test PC PSU output ripple without an oscilloscope?

Seriously, why bother? Whatever you may measure, you can't easily influence it, and at the levels a computer SMPS produces, ripple is not that critical. If you are really concerned, buy a higher rated PSU, ripple increases when you load it close to the max.

Cheers

Billy 8-{)

Agent_24
11-10-2007, 06:48 PM
I can throw the PSU away if I find the ripple is too high :D

Seriously, some of those cheap PSUs are damn crappy, they'd probably violate ATX spec for ripple with no load.

In fact I believe some of the reall bad ones have stickers that actually state ripple higher than the maximum allowed anyway


But aside from that, what do you think of the kit from jaycar (or the LPTscope project)? how useful do you think either of them would be for a measurement device, for anything, not just PSUs?

Terry Porritt
11-10-2007, 07:37 PM
The frequency response, or bandwidth of sound cards is too small to measure the switch mode frequency ripple with any certainty. They are limited to audio range, say up to 20kHz, whereas the switch mode frequency will be 25kHz or higher, maybe 50kHz.

There was also a very similar device to the Jaycar EA kit in the August 2002 issue of Silicon Chip.

You really need an oscilloscope so that you can see waveform, though an AC millivoltmeter of suitable frequency range, like the now rather ancient HP 400E would give an indication.

Even if you did use the Jaycar kit, in order for any measurements to be meaningful, you would need superior equipment to calibrate it :) Hence that superior equipment itself could be used to measure ripple.

Billy T
11-10-2007, 07:41 PM
But aside from that, what do you think of the kit from jaycar (or the LPTscope project)? how useful do you think either of them would be for a measurement device, for anything, not just PSUs?

I think both have limitations that will reduce their effectiveness at PSU switching frequencies. I have a two channel PicoScope ADC-200 100MHz scope which runs though my laptop, a three channel 40MHz scope, and a Fluke 43A PowerMeter which includes a single channel 20MHz scope. The latter is adequate for fast rising waveforms such as those from SMPS units, but an audio scope is going to struggle to show much of value.

I'm not saying you won't find it useful to some degree, but how useful will depend on your prior experience with scopes and your ability to interpret what you see. I still don't think it is worth it though, I can't see what problems you might have that are caused by ripple unless it gets so bad it affects the sound. I'm willing to learn if you care to explain though.

Very good scopes are available on TM from time to time and one may just suit you better. If you are patient you can buy at very low prices. I got my 3-channel 40MHz scope for $200 which was damned good buying. Quality probes are essential too, and they may end up costing more than the scope!

Cheers

Billy 8-{)