Transformerless power Supply – 24VDC, 120V AC and 230V AC

acdcpower supplysafetytransformerless

I want to know if it is possible to design a power supply for a circuit that can operate from DC and AC using the same input terminals.

Thus, the output should be xxV DC (5-24 or whatever is decided on), and on the input side the consumer can connect whatever he has available – 120V AC, 230V AC or 24V DC.

A transformerless AC to DC power supply can work for at least the AC side, but the ideal one looks to be the capacitive type which would not allow DC to get through, am I correct?

There is also an resitive transformerless design, not ideal at all since it is very ineffecient.

Capacitive Transformerless Power supply

Any ideas? Thanks!

Best Answer

I want to know if it is possible to design a power supply for a circuit that can operate from DC and AC using the same input terminals.

Yes, this could be called an off-line switched-mode converter however, it is usually not a good idea to omit the transformer because: -

  • It offers protection to the low side voltage due to it isolating the dangerous live voltages
  • It offers higher power solutions

enter image description here

The above picture shows how it works. It should be noted that "AC line" can actually be a DC line input. The isolation transformer is in the block labelled "DC-DC convertor".

Another name for this topology is "fly-back converter". The bridge rectifier at the front end ensures AC and DC power inputs are adequately converted to fairly "steady" DC voltages.

If you have a good argument for not using a transformer then I'd like to hear it but, be prepared, it's unlikely that you will.