Hardware Insights Forum

These "modern looking" low end PSUs are criminal. Half-bridge primaries were bad circa 2007, in 2013 it's abysmal... This collection of beauties were powering a C2D, i5-750, & i7-860...

That's bad. I really wouldn't use those with a high end PC (or any PC for that matter)

Are half bridge primary switching transistors really that bad, assuming you have really good, TO-3P ones with very good cooling and heatsinks? I understand if half bridge's limit is somewhere around 550W, but even then...

They are just very inefficient compared to forward. Considering how many affordable single transistor and two transistor forward PSUs are out there (like In Win Power Men), there's just no excuse to still use it.

Do you mean the way half bridge PSUs use bipolar transistors instead of the MOSFETs found in forward PSUs, so they're quite a bit more inefficient, and that it results in more of a switching loss of sorts?

Yes. Bipolar switching transistors like 13007s and 13009s have much slower switching times than MOSFTEs, which means that they take longer to switch on and off, which is when switching losses are at their highest.

This may sound silly, but... I take it there isn't really such a half bridge design that uses MOSFETs on the primary, is there?

No. It's impossible.

Wester547,

c_hegge wrote:Bipolar switching transistors <snip> have much slower switching times than MOSFTEs

That's the key, switching speed. You can build a higher powered PSU with half-bridge, but the pennies you save there cost elsewhere. You'll need decent heatsinking, more bulk storage & larger main transformer. For example a Delta/Newton 350W dual P2/3 era PSU (~2000), employed a 10A bridge, 2x 1000uf primaries & ERL39 transformer all for only 15A@12V & 35A@5V. Now, the VRD specs were quite different then, but when circa 2010 half-bridge designs have 4x1.5A diodes, 2x560uf primary caps & ERL35s all on ATX spec 2.01 PCBs yet tout >20A@12V - call me unimpressed. That's without even looking at the secondary side.

c_hegge wrote:That's bad. I really wouldn't use those with a high end PC (or any PC for that matter)

Yeah. A friend upgraded his P4s to the Lynnfields. Thought he'd save a few bucks by reusing his components. I installed Seasonic S12 550w units a week later...

OT. I had an inkling you were doing the crappy PSU roundup pre-Christmas & was going to contribute a few of these units. Just didn't get around to it. I'm happy to send them to you for the next installment of measured torture.