Automatic switching between 110 and 230 VAC


Thread Starter

John Yew

I know of the manual selection of mains voltage using the voltage doubler principle. What I am looking for is an automatic mains voltage switching for use in appliances used by worldwide travellers. Thank you.

Eric M. Klintworth

Every one with which I am familar, such as my electric shaver, uses a switching power supply. Switching power supplies typically accept a
wide range of input voltages, for example 90 volts to 250 volts.

Eric Klintworth

Frederic Ioset

If you want to make yourself an easy power supply which is ok from 85V to 264V for 50 and 60 Hz
You can use the component from Power integration.
just about all 'universal input' power supplies are indeed switching power supplies. this has to do with the way the input is treated.
what is used is two stage conversion: first one is AC/DC and the second one is DC/DC.
second stage (DC/DC) needs no adjustment when input is changed form 120 to 230vac and vice versa because FIRST stage will make sure that input DC voltage is always in same range (only few volts more or less).
i assume you understand that standard AC/DC stage
typically uses only bridge rectifier and
an electrolythic capacitor.
but in our case there are TWO capacitors which are in SERIES. wiring a relay contact between one line input (one of the AC contacts) and midpoint of the capacitors allows control of the DC voltage fed to DC/DC converter.
when input is 230vac, AC/DC stage works like the plain bridge/cpacitor circuit providing some 300VDC for DC/DC stage.
when input is only 120vac, contact is closed and output is doubled to 300VDC.
closing contact when input is 230VAC would create 600VDC and destroy DC/DC converter but this can be avoided with design of the relay circuit. only when relay fails (weleded contacts) the power supply is gone.