Question about the circuit board

VERY, VERY unlikely - if it's suitable for operation on 220V then it will say so on the outside - it's got nothing to do with the voltage ratings on the components.

Generally, to be multi-voltage, a unit would require a SMPSU - which I wouldn't expect a hairdrier to have.

The pictures aren't a power adaptor anyway, they look to be a simple mains filter, to prevent interference.

I would imagine plugging it in to 220V would destroy it in seconds.

Those X2 capacitors are rated for 275 volts. The peak voltage of 220 VAC is 220 × 1.414 = 311 volts – oops, you let out the magic smoke. Rest in peace smoky the hair dryer.

Nigel Goodwin is right anyway – the box is just a filter.

There are 110/220V dryers out there, and are clearly marked as such. Your 100V (120V) unit will not operate directly on 220V, you will burn up the heating elements.

sagor1 said:

Your 100V (120V) unit will not operate directly on 220V, you will burn up the heating elements.

Click to expand...

And the filter caps. And the motor.

It's possible the filter is universal, as the caps are rated 275V AC. But, I suspect the 330V varistor rating is too low for 220V anyway, as they usually have a 10% accuracy, and the peak voltage (311V) would be too much. But regardless, the motor and elements won't survive anyway. The unit is 110V only...

Rated AC voltage is always assumed to be sinusoidal RMS AC not peak or DC. So 275V is OK. and the varistor might blow the fuse with a grid transient.

The heater naturally needs to be increased in resistance by 220 % while maintaining the motor current, so good luck..