Re: Isolated power supply design


"Ethan" <idethan@xxxxxxxxx> wrote

> The patient site
> is only about disipating about 30mW. You can't put too much power
> here. It's bad form to burn an unconscious person.

Burning the unconscious is exactly what some of my designs intend!
But it is important to put the burn where the surgeon wants it.

> If I don't put all the patient isolation into the mains power supply my
> architecture gets really complicated.

Not that complex, really. Standard design for ECG amplifiers includes
a transformer-isolated power supply at a few MW providing the power to the
preamp, then some clever way of sending the signal back across the barrier.
Or at least that was the way we did it a generation ago...

For 30mW, you don't really care about efficiency, just isolation
(4KV standoff MINIMUM)and low,low leakage current. It's a handful of
cheap components costing a few bucks.

Think about how much simpler any supply design is with 30 dB less power to
handle.

I'm also thinking about the capacitance you get for free with a larger
physical
package 'inside the barrier'.

Regards
PN2222A
Tf (fall time) 60 nS
See figure 2


.

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