topology: how to do p-channel depletion that's HV safe and have full swing?

Beats me. Supertex makes N-chanle depletion MOSFETs

But I've never comes across a P-channel depletion mode part.

-- Bill Sloman, Nijmegen

Same here.. This stinks :/ There appears to be numerous patents for manufacturing techniques of p-channel depletion mode mosfets, but looks like no one actually makes any.

I've never thought about this before, ever, until I realized I needed one.

Too bad this circuit idea of mine will never happen..

You can't rely on that. Back around 1974 I had a neat, but - at that time- impractical idea for reducing the ripple on a PWM output. Nearly twenty years later, when tackling a similar problem, I realised that I could I could program a single PLD to do the job and put the idea into practice. It worked.

-- Bill Sloman, Nijmegen