250 Volt DC input for an ATX PC power supply?

[ali765]

Hi,

Normally, an ATX power supply requires 220 volt AC input. But it converts AC input to DC, before switching.
In this case, can I choose DC input for an ATX power supply?

If yes, what is the required voltage? 250 volt or higher?

Thanks

 

[Nigel Goodwin]

Hi,

Normally, an ATX power supply requires 220 volt AC input. But it converts AC input to DC, before switching.
In this case, can I choose DC input for an ATX power supply?

If yes, what is the required voltage? 250 volt or higher?

It depends on exactly how the power supply works, but generally they are quite happy fed from DC - you need about 340V DC - which is recified and smoothed 240V AC.

 

[Sceadwian]

I don't think the compliance voltage for an ATX power supply is usually listed on the case or can be easily found out but Nigels value is an RMS to peak equivalent, so it should be fine. ATX supplies are built with full wave bridge rectifiers, feeding a full wave bridge with a DC voltage is going to cause one branch of the bridge to pull double current duty and the other to be completely unused. If the diode bridge is discrete you may fry the bridge diodes in short order, if it's a square packaged full bridge the risk is mitigated slightly by the package being very closely thermally linked but you should DEFINITELY de-rate the power rating of the supply by 25% minimum, and I'd say 50% if it uses a discrete bridge and if possible you should open up the supply and bypass the bridge completely. In this situation it's just wasting two diodes drops worth of power anyways. On the plus side the input filter capacitor will be used more as a bypass capacitor than a filter as there's no AC except what's generated by the load.