Switching power supplies without APFC generating least AC harmonics

[japlytic]

In an Xbox 360 external power supply, it does not have active power factor correction (APFC), but uses a half-bridge topology (I incorrectly said elsewhere that it had a push-pull topology )

Which switching power supply topology (without APFC) would generate the least harmonics on the AC line?
The switching topologies I can think of are the forward converter, the push-pull converter (B+ is at centre tap), the half-bridge with a single input rail (i.e. 340V DC), a variant of the half-bridge, which has a centre-tap from two 200/250V electrolytics to generate positive and negative HV rails like in old-school style computer power supplies, and the full bridge.

[tom66]

Re: Switching power supplies without APFC generating least AC harmonics

The Xbox 360 PSU -does- use APFC because it consumes about 180W and is sold in the UK and Europe where APFC is almost certainly required.

In your pic:-
https://www.badcaps.net/forum/attach...7&d=1336720274

You can see a yellow-coloured like transformer which is unaccounted for - this is the APFC inductor. Also 180uF is too small if it wasn't using APFC.

I'm guessing one FET is for the APFC, the other is for a single-switch forward topology of some kind (good for output power <250W and quite efficient.) There is a through hole diode somewhere too I expect.

As for least harmonics - one of the newer resonant tank converters which switch sine waves into the transformer (but really efficiently using MOSFETs as on-off devices.) It is quite common to see that kind of topology in LCD TVs.

[PeteS in CA]

Re: Switching power supplies without APFC generating least AC harmonics

If I understand your question correctly - speaking generally, not to the Xbox specifically - the harmonics reduced by PFC are a product of the capacitor filtered rectifier circuit. I don't think the inverter topology (full bridge, half bridge, forward converter, flyback) matters much, if at all.