PWM in a switching power supply

w_tom wrote: That supply does not provide

W_tom, you are wrong, the primary side is insulated by 3 transformers T2,T3 and the always on +5V supply T6. Depending on these transformers will be the isolation, maybe even 1200-2000V for a short time. The outputs and the internal circuits are not isolated from each other, which saves a lot of optos and associated transmission problems. The same is true for the power good line and the PS-ON line. I wonder why there would not be galvanic isolation?

w_tom wrote: That supply does not provide

W_tom, you are wrong, the primary side is insulated by 3 transformers T2,T3 and the always on +5V supply T6. Depending on these transformers will be the isolation, maybe even 1200-2000V for a short time. The outputs and the internal circuits are not isolated from each other, which saves a lot of optos and associated transmission problems. The same is true for the power good line and the PS-ON line. I wonder why there would not be galvanic isolation?

Pete,

Those are all good points, but keep in mind why chips such as National's "Simple Switchers" are so popular: Many relatively inexperienced engineers are given the job of designing relatively undemanding switchers, and they use whatever they can to get the job down as best as possible. I think it's a safe assumption that if someone can't tell you why a "Simple Switcher" IC isn't an all-purpose solution, it's the kind of chip they should be using! :-)

I am all for people learning traditional filter design theory. It's unfortunately an area that's slowly dying due to more and more filters being able to be replaced by DSP techniques.

---Joel Kolstad