Thermaltake Toughpower 750W ATX power supply

[Maxpayne]

This is output section of Thermaltake 750W ATX power supply.

Can somebody explain what is the role of this ckt in +5V rail ?

Two transistor forward topology is used here in the primary. I don't have the whole schematic, also looking for it

My problem is in +5V section. Whenever I connect load on this rail the power supply shuts off itself. other two rail +12V and +3.3V is quite ok.

[b700029]

Re: Thermaltake Toughpower 750W ATX power supply

That schematic doesn't look quite right... as the transformer is center-tapped the dual diodes should have both ends connected to each side.

[Maxpayne]

Re: Thermaltake Toughpower 750W ATX power supply

This is right. I hv chked it..

[Khron]

Re: Thermaltake Toughpower 750W ATX power supply

Which 750w ToughPower model is it?

[Maxpayne]

Re: Thermaltake Toughpower 750W ATX power supply

Thermaltake Toughpower 750W wired

http://www.hardwaresecrets.com/artic...r-Supply/369/3

[Th3_uN1Qu3]

Re: Thermaltake Toughpower 750W ATX power supply

The arrangement of the diodes is normal for 2-transistor forward configuration (half wave rectification).

[Maxpayne]

Re: Thermaltake Toughpower 750W ATX power supply

What is the role of PNP transistors and TL431 circuitry ???

[b700029]

Re: Thermaltake Toughpower 750W ATX power supply

The arrangement of the diodes is normal for 2-transistor forward configuration (half wave rectification).

Almost all the ATX PSU schematics I've seen have full wave and center-tapped transformer, like these:

http://320volt.com/wp-content/upload...tx-circuit.png

[Th3_uN1Qu3]

Re: Thermaltake Toughpower 750W ATX power supply

Yes, but that is half bridge. In two transistor forward topology it's impossible to have a center tap and full-wave rectification at the output because the input is single ended, the two transistors switch at the same time, so the magnetic flux in the core only goes one way, hence the output voltage will only go one way as well. You could say the core has a DC bias if it helps you to visualize the situation. Same goes for all single ended topologies: single transistor forward, two transistor forward and flyback.

[b700029]

Re: Thermaltake Toughpower 750W ATX power supply

Thanks for the explanation.

I thought two transistor forward wasn't used at high power levels and half bridge was more efficient?

[Th3_uN1Qu3]

Re: Thermaltake Toughpower 750W ATX power supply

Somewhat true, but the marketing in current day ATX PSUs says otherwise. Since the bottom-of-the-barrel Chinese manufacturers have been doing the same outdated halfbridge designs (since that's all they could copy) for over a decade, the high-end PSU companies producing for enthusiasts had to add something new to the marketing, and so they oriented towards double forward.

In high power units (1kW+) there's a resurgence of full bridge designs.

In the book, "Switching Power Supply Design, Third Edition" there is a comparison made between double forward and half bridge, and ultimately they are pretty much one and the same in terms of power per $$. The number of turns in a double forward transformer is double that in a half bridge - but since the transistors switch the full input voltage not half of it, the current is halved, so thinner wire can be used and the overall copper cost remains the same.

Where there IS a difference is in core flux - since the half bridge switches the flux alternately one way and the other, allowable flux density for a given core is practically doubled. In ATX PSUs this makes little difference however, as most if not all ATX transformers are copper loss limited, since they have to deliver high currents. In a higher voltage application, such as a power supply for a large audio amplifier, there may be a difference in favor of the half bridge.

In my experience, i've been able to squeeze *a little* more power from a given core size in a half bridge PSU, but the difference is no more than 10%.

[b700029]

Re: Thermaltake Toughpower 750W ATX power supply

Interesting, so in other words they're taking a topology that's not recommended to go beyond ~500W from most of the references on the web I've found, and pushing it beyond that for marketing reasons. So I guess it's possible to make a real 750W half-bridge too.

[Th3_uN1Qu3]

Re: Thermaltake Toughpower 750W ATX power supply

So I guess it's possible to make a real 750W half-bridge too.

Well, i built one that does 650W myself, i don't doubt that with a little bit of care i could squeeze that extra 100W out of it.