Rewound MOT Switched Multi Winding Binary Voltage Power Supply


A power supply capable of supplying 1000W or 16A (Whichever is lowest) at any voltage between 0-255VAC or 0-320VDC in 1V steps.

It consists of a rewound Microwave Over Transformer (MOT), with 8 windings, whose voltage outputs are as follows:

  • 1V
  • 2V
  • 4V
  • 8V
  • 16V
  • 32V
  • 64V
  • 128V

Hence any voltage between 0V and 255V in 1V steps can be attained by wiring a number of these windings in series.

The following schematic shows an implementation of this idea, using relays to wire the chosen coils in series.
An 8 bit parallel binary signal should be connected to the 8 control inputs (at the bottom of the screen). The output will be nVolts where n is the binary value of the signal at the control inputs.

E.G. a voltage on the 64V and the 8V and the 2V control inputs will give a 74V AC output.

Power Schematic

This schematic shows the transformer, inductive ballast, and relays.


I used a PIC18F4550 programmed with this code to control the relays.

The voltage is set by the potentiometer.
The display can either show the measured voltage, or the set voltage.
The displayed voltage can be switched between RMS or peak.

When the voltage has been selected with the potentiometer, the set button is pressed. This sets the relays so as to output the set voltage.

A common-anode 3 digit 7-segment display is used.

PORTA is used exclusively for the ADC input
The voltage adjustment pot connects to RA0

PORTB drives the power supply's relays

PORTC is used as inputs for the switches
Bit0 of PORTC connects to the voltage set switch
Bit1 of PORTC connects to the switch which selects RMS or peak voltage display

PORTD drives the 7-segment displays' cathodes
Bits 0 through 6 of PORTD drive segments A through G respectively

PORTE drives common anodes of 3 7-segment display digits
Bit0 of PORTE connects to the anode of the hundreds digit
Bit1 of PORTE connects to the anode of the tens digit
Bit2 of PORTE connects to the anode of the units digit

Control Schematic

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License