Electronic – Transformer winding tap switch without relay

switchestransformer

I have a transformer with four taps and I use two relays to switch between them:

schematic

simulate this circuit – Schematic created using CircuitLab

When both relays are energized, they consume ~60 mA which really is a waste. I want to switch between taps of transformer with something that draws less current.

I was thinking to use four logic-level mosfets but mosfets have an internal diode which will do unwanted half bridge rectification…

What options do I have other than relays and mosfet to switch between taps of transformer?

Edit:

12 V Relays are on the secondary side of transformer, relays and controller (MCU) are powered from another winding of same transformer which is independent from this four tap winding.

Best Answer

You may use magnetic latch relays which require only a short pulse to set or reset.

Here's a schematic, using a diode matrix, 3 push button switches and 3 magnetic latch relays.

enter image description here

Freewheeling diodes for the relay coils and LED indicators are not shown.

'NO' contacts of the relays K1, K2 & K3 are to be used to select the taps.

How it works:

  • The 'S' (set) coil of a relay switches the coil one direction and it remains there by magnetic action.
  • The 'R' (reset) coil of a relay switches the coil in the opposite direction and it remains there by magnetic action.
  • Pressing S1 momentarily 'sets' K1 and 'resets' K2 and K3.
  • Pressing S2 momentarily 'sets' K2 and 'resets' K1 and K3.
  • Pressing S3 momentarily 'sets' K3 and 'resets' K1 and K2.
  • The diodes prevent backfeed from one switch into the circuit of either of the others.
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