Power Supply Question

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I salvaged a power supply board from an old computer monitor. It has 5 and 12 V outputs. I want to use it to power and avr and drive up to three,1 A power LEDs. How can I determine what the max load is that the supply can handle?

Thanks,
Leor

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If the board itself has a model# or some type of identification try typing that into google. You may get a spec sheet or so info.

Self proclaimed Captain Link

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The module is probably a custom. If so, it won't show up in google at all. I'd try to find specs on the transformer, rectifier (or diodes), and/or the DC-DC regulators. The latter may well be easiest to find and will quite possibly be the limiting factor, current wise.

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For a monitor, I'd bet that the 5V supply could deliver at least 1 amp.

Go ahead a try it for your project. What do you have to loose. If you draw too much current, you won't hurt the supply (which was free, anyway). Instead, it will current limit and the voltage will just drop below the expected voltage.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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I found the part number. It's a Part II Research ct-9202a. There is also a 2A fuse on the high side.
It's a switching supply.
Thanks.

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Be careful, it might not have any mains isolation.

Leon Heller G1HSM

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I also might require a minimum load, depending on its age and who designed it. :)

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for the avr and 3 leds It doesn't seems to be too much power.

I don't think there is an experimental way to find this, but there is no much to lose if you connected it to your circuit directly.

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If you're scrathing for a cheap power supply , scavenge one from an old PC. There's little doubt if will have enough current on the 5V line to power your load. You might need to plug in a hard drive to provide a dummy load though.

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Quote:
If you're scrathing for a cheap power supply , scavenge one from an old PC. There's little doubt if will have enough current on the 5V line to power your load. You might need to plug in a hard drive to provide a dummy load though.

There are some examples on this at instructables. Here is the first one that popped up for instance. http://www.instructables.com/id/Another-Benchtop-Power-Supply-from-PC-Power-Supply/

Self proclaimed Captain Link

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If it has a 2A fuse shouldn't it be able to supply at least 1A? (with a 50% design margin)

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The 2 Amp fuse is on the high side. It will blow if you exceed 220W (2 Amp x 110V, assuming USA).

Your circuit will consume 3 Amps @ 5V -> 15 Watts max.

It is probable that the power supply delivers most of its power on the 12V rail. You probably want to connect the entire load to the 5V rail to limit heat dissipation over the current limiting resistors. Your LEDs will run at about 3V, if you want to control them individually you'll burn 2W/LED over the resisitor from the 5V rail and 9W on the 12V rail. If you put them in series you'll burn once 3W on the 12W rail, which is quite acceptable.

Markus

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Thanks all for the replies!