What Bandwidth O-Scope for SMPS/Linear power supplies?

[TheLaw]

Hi,

I'm getting into electronics quite a bit. My main attraction is power supplies at the moment. I've been putting together a collection of switching and linear supplies ranging in all sorts of topologies.

I'd like to buy an O-Scope off ebay or maybe one of these new DSO o-scopes on SeeedStudio.

However, I don't know what frequency range and/or how much bandwidth the scopes need to measure. (Weird wording, sorry). Is 30Mhz sufficient? Or do I need more? Like 100Mhz? More?


Thanks.ss

[Spectre]

20MHz

[TheLaw]

Thanks!

[Travis]

If you're going to measure the rising/falling edge of SMPS or the switching transients with some high frequency details, 100MHz bw should come in handy since higher bw means faster response.

[dish_moose]

With SMPS having faster switching frequencies(more efficient smaller inductors) the rise time and dead time have to be very fast. A slow scope cannot display the rise and fall times correctly. Linear supplies - a 20 MHz scope will work fine. SMPS need fast scopes with the proper probes otherwise the noise induced in the probe will be what you measure.
-Bruce

[Digerati]

I have always been taught to go by the rule of thumb and try (if budget allows) to purchase a scope with a bandwidth five times higher than the maximum frequency to be measured. This is to ensure you capture up through the 5th harmonic so you can get a sharply defined waveform (and to spot anomalies).

I think, unless you will be limiting your testing to slow switching devices like power supplies, it is a mistake to buy a scope that will not really help you with your other electronics - like testing high-speed USB3.0 ports.

You should look at the fastest scope your budget will allow - then double it.

If me, I would get no less than 200MHz, but frankly, I would be looking at 2GHz to hopefully ensure the scope's usefulness further into the future.

If budget is really tight, I would still wait until it can be increased to afford at least the PicoScope 3000 Series (http://www.picotech.com/oscilloscope.html), or something similar.