I am new to electronics and working on building regulated linear bench power supply 0v to 30v, 3A as my first project.

For better performance, wanted to switch between multiple tapas of ac-to-ac transformer depends on required output DC voltage. So my switching device(relay/ some other) output will feed into full bridge rectifier and then voltage and current control circuit.

What is the best method to switch between transformer taps other than relays? Any example semantics and part numbers?

The transformer taps 12v/24v 100va.

Thanks for the help.

  • \$\begingroup\$ I would go for relays. Have you looked at a schematic for a commercial one for inspiration? \$\endgroup\$
    – winny
    Feb 19, 2021 at 7:35
  • \$\begingroup\$ Thanks for the advice. i am searching designs, I am fairly new and taking long time to understand. \$\endgroup\$ Feb 24, 2021 at 18:46

1 Answer 1


I've seen that often in linear supplies and they usually did it with relays.

I guess that doing a tap switch with TRIACs or SCRs (essentially the same thing) would be a good solution. It could be a little inconvenient to drive the gates, however, and for 3A probably sticking to relays is better (unless you need to continuosly switch range). An SSR (which is usually a pair of SCRs with some opto circuitry) would be a good compromise.

For you information (for later projects!), these day the common practice is to use a switching converter to pull down from the high voltage rail to something like a couple of volts more than you target voltage and then use a linear to do the final regulation (and less noise/ripple). This is of course more complex but much more efficient.


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