Will this work-zener variable regulator

[mikemac]

I have used this circuit before
[link]
Please ignore the heaters and the doubler, its the bit in the bottom right hand corner, with the zeners..........
My questions are
The two 130v zeners set the 260v output. If i switched the top zener to earth, at the bottom, i would get 130v output. is it feasible to have a string of zeners for pre determined voltage switching, say 60, 120, 180, 240, 300 by stringing 5 60v zeners.
What would be a foolproof way to swich them, they would have to be in order?
What would happen if they were switched "hot"?

[godfrey]

The main thing is to make sure the output is never left "floating". Below is the relevant part of your circuit, and a pic showing how to have switchable voltages.

[mikemac]

and if it is switched whilst hot? might be redundant but just to be sure

[mastodon]

I suppose that as long as the voltage reference at the gate of the mosfet is buffered with a capacitor, the transition to the new voltage should be fairly gradual, depending on the cap used. The most important thing to think about is the power dissipation of the mosfet in different voltage/power demand regimes. E.g., if your supply is optimized for 260V @ 100mA, and instead you switch it to 130V, but still draw the same current, the dissipation of the mosfet will rise by 13W since the input voltage stays the same.

[Chris Daly]

In your diagram there is way too much voltage through through the switch. Use 4 single pole single throw relays with 4 switches, to get each of the voltages values at any given time . There are numerous possibilities with connecting relay contacts and switches - that will if carefully deployed enable any switching sequence you can imagine. For the coil that is activated by the switch, you can arrange this to be either simple with the coil voltage applied ie 5v-12v but use a 1N4004 diode and capacitor 10nf to stop back EMF or arrange the coil to activate by a NPN transistor where better control can be arranged.

Relays are your answer, use a zener calculator on google or other to ascertain the resistor value, for the zener stack. there you can work out how much wattage is necessary to bias the zener string for a given load. Happy switching.


Cheers / Chris