Possible to boost 12v amp ?

[Gabriel]

Would it be possible to increase 12v from 560mA to 1.5A without replacing transformer ?
Got this at the dump and thought I modify it with a molex plug to power a external harddrive but 12V amps is low rather low.

[mariushm]

Re: Possible to boost 12v amp ?

Probably not... won't raise it significantly without messing the 5v output.

But what you could do would be to get a boost dc-dc converter to boost 5v to 12v and place it inside the power supply... something like this would do the job just fine.

[momaka]

Re: Possible to boost 12v amp ?

Interesting design. Looks like the 5V rail uses a schottky diode and is the one that the PSU regulates against while the 12V rail is left hanging without feedback (hence why that LM317 linear regulator is possibly there). Or the actual output of the 12V rail is higher than 12V and that's why they used the LM317.

Either way... I think it might be possible. The limitation of the PSU is 26W, so if you are to make this PSU purely a 12V adapter, it would be able to do 2A at 12V.

But first we will need a better picture of the board's solder side (preferably looking straight down on it). There's a 358 op-amp and a second optocoupler. Need to understand what those do before messing with anything, because this doesn't seem like the simple flyback design with just a single optocoupler.

[goodpsusearch]

Re: Possible to boost 12v amp ?

Note the capacitance of the output caps and what caps are on the 12V output and 5V?

[Gabriel]

Re: Possible to boost 12v amp ?

Ahh will have a look at the dc-dc converter if nothing else works out, I might be able to squeeze it in if I remove the RX30,lm317 and its heatsink.

Took a few new pictures and marked in caps, this is the first psu I ever see with a Rybycon Rx30 130C.

I need both the 12v and the 5v to power a internal harddrive.

[PeteS in CA]

Re: Possible to boost 12v amp ?

The key factors are the adapter power rating, the +12V transformer winding, the +12V rectifiers, and the LM317. If you minimize the load on the +5V (so more of the rated power can go to the +12V, you may be able to evade that issue. The +12V rectifiers should probably be rated for 6A-10A (the higher the rating, the lower the forward drop at actual current, which reduces wasted power). While an LM317 rated for 1.5A is probably available, I'd suggest getting a 1.5A rated LT1086. The LT1086 is pin compatible and has the same internal reference voltage, the difference being that it is a low drop-out voltage part. That means the regulator can regulate with a lower input voltage than the LM317; that may be necessary with a light +5V load. The one thing you cannot do much about is the +12V transformer winding. Delta Products is a good company, so they may have been a bit conservative in choosing the current capability of the +12V winding, which would be a good thing for your purposes. You may be able to mitigate the higher temperature some by having a fan blowing on the adapter.