Problems with 12V and 5V lines on a PC ATX supply

Maybe because its not well designed.Switch mode supplies tend to be designed with a minimum load in mind in my experience. Brian

AS I said, its all part of the fact that its switch mode, and the regulation is not a classic series regulator, its a feedback loop controlling the oscillation of the switch mode part, its all interconnected. I first encountered this weirdness many years ago when a pc I had had some tacky bright leds all down both sides of the front, making it look terrible and for me making my failing sight rebel. So I thought, simples, unconnect them. It was then that the pc decided it either would not start correctly or would not shut down an and lots of tother things went weird. Reconnecting the leds and all was well again. In the end I hid the leds in the case. Out of sight out of mind. I expect the spiders enjoyed it. Brian

I can understand it going off with a high load, but zero or low load is just weird.

That's weird. Surely the LEDs weren't the only thing drawing power at that voltage?

I might try this, as it looks very much like the one I bought to fit in the local restaurant to power a huge amount of LED mood lighting, and that's still working after 5 years:

I'm surprised there aren't dedicated transistors for every line.

How can it be so hard to monitor the voltage when there's no current flow? And how can 12V be down at 10.5V when 5V is up at 5.2V?

Why do those two detections need to be related?

It's getting plenty current through the 12V part, which must be physically larger (as in more coils) than the 5V part. I can draw the full 56A from 12V, and it's still unhappy?! By the way, the 5V is only 33A max. So, 1.5A on 5V makes it happy and 56A on 12V does not? What gives?

The guy who designed that circuit must have been on some wild drugs. "I know, let's make things more complicated than necessary and make assumptions about the current draws when it will be connected to a computer that could have any number of different parts operating at different voltages, some of which may not be used some of the time."

Or buy a single power supply that can handle the full load. They DO exist, but they ain't cheap!!

There's a group sci.electronics.design that still has life. They might like the diversion from arguing the merits of the electoral college.

The scottish wanker loaded the same question to all the electronic groups at the same time. Playing off one set of groups against the other.

I was born here, and voted independance.

Playing off? WTF are you talking about? Since I don't inhabit those groups, I don't know which have any traffic or anyone who can answer, hence I asked in all the relevant ones.

I shall try it.

You are asking all the same f****ng questions as you have done here - and amazingly getting all the same answers. But still you persist.

Of course I'm asking the same questions in different groups, to perhaps find someone who has the intelligence to answer them.

We all did, you are too stupid to understand the answer.

Did you get your "Does a parrot's foot conduct electricity?" post answered on the s.e.design group?

I understand alright - that designers are morons.