Scope analog bandwidth for designing SMPS?

Hello,

What is a suitable analog input bandwidth for a DSO scope that can be used for designing offline flybacks for up to 40W?

Switching frequencies is 100KHz or less.

(Please wait for others to respond, because I'm quite a critic of 'scopes).

As a general margin, with square wave switching frequencies, then I'd multiply that freq. by 20 as a minimum. i.e. for switching freq. 100kHz then scope freq. 2Meg minimum.

Actually, I am so critical of 'scopes that we have 2 at each end of a workbench - sometimes the artifacts displaed on one will not be apparent on the other. With DSOs, the sampling artifacts can be very misleading, so it depends on the specifics of the job in hand which 'scope I'd choose to use for any particular job. For some linear circuits, a simple analogue, low bandwidth 'scope can be more revealling than a more expensive digital 'scope which can confuse artifacts in the DUT with artifacts of the 'scope.

In SMPS I've designed, I've seen bandwidths of 25MHz and up. For looking at transient events, sampling rate is as important as bandwidth. Personally I'd want 100MHz of bandwidth and 1Gsps (for both of two channels) sample rate.