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+12/-12/+5 bipolar PSU circuit


fussylizard
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Hi fussylizard, in a classic linear design, the large capacitor between the rectifier and the regulator is used as a 'reservoir' to smooth out the rectified AC and to supply the regulator with top up DC, when large load spikes are experienced.

Its also a good idea to put a low value resistor in series with the recified and smoothed DC and the regulator. This makes up a passive R/C low pass filter, removing any residual ripple, making the job of regulation easier for the IC. The resistor is usually chosen to match up with the capacitor so as to make the cuttof less than 50 Hz. I forget the math for this, but it should be out there. The other thing to keep in mind is that components are not perfect, and a large electrolytic capacitor will have some resistance. For this reason, it can help to put a smaller capacitor in parallel with the reservoir capacitor.

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  • 1 month later...

Hey all,

Just a quick recap on where things are. I got the board made (BatchPCB) and it tests out fine. I went ahead and built it with a standard 7805 regulator which gets *very* hot (not surprisingly!) but I wanted to test it out. I'm going to order a switch-mode 7805 drop-in replacement to handle that problem. They are about $15 a pop, but have very high switching frequencies so I should be OK even if I drive an AOUT_NG and SSM filter (which is the plan!).

Two pics to share-

Here's the populated board:

post-6425-0-99782500-1315801094_thumb.jp

Here is my PSU board mounted in my MB-SEQ. I'm using the same case that Altitude used, though I'm quite a ways from being 100% complete on it. You can also see in that pic a prototype of Altitude's 4xIIC board, as well as my painting of the base (in-progress...first attempt was a train wreck...)

post-6425-0-75865300-1315801103_thumb.jp

Will let you know how the switching regulator works out...

Regards,

C

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You can also see in that pic a prototype of Altitude's 4xIIC board,

interesting interesting!!

that would be my next step, to design a 4x IIC out board and have Mike make it (and to be honest, have him check it and ask a bunch of not so clever questions too :blush: )

but... if there's gonna be some ...availability.... i might be able to not kickstart my brain

:whistle:

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Oh BTW you can see in the pic that I mounted the caps horizontally to save vertical height in the case. That's why all the caps are along the edge like they are. Worked out pretty well.

Curious as to why you have so many caps? 3 for positive/gnd and 3 for gnd/negative or something?

As far as the heat, you don't appear to have a on those regulators and that should make a *BIG* difference. Be careful not to connect your heatsink solution to both the positive and negative regulators though. For the positive regs, you should be able to even use the metal chassis as a sort of heatsink.

EDIT: Aha, I think I figured out what you're doing with the caps. It looks like you are using a multi-out transformer? If so, got a model number? I've been looking for something like that for a while.

Edited by m00dawg
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interesting interesting!!

that would be my next step, to design a 4x IIC out board and have Mike make it (and to be honest, have him check it and ask a bunch of not so clever questions too :blush: )

but... if there's gonna be some ...availability.... i might be able to not kickstart my brain

:whistle:

Here's the thread about the 4xIIC board:

I'm not sure what Altitude's plans are for it. I was already ordering some stuff from BatchPCB so I ordered a prototype 4xIIC board for Altitude at the same time. Maybe drop him a PM?

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Curious as to why you have so many caps? 3 for positive/gnd and 3 for gnd/negative or something?

As far as the heat, you don't appear to have a on those regulators and that should make a *BIG* difference. Be careful not to connect your heatsink solution to both the positive and negative regulators though. For the positive regs, you should be able to even use the metal chassis as a sort of heatsink.

EDIT: Aha, I think I figured out what you're doing with the caps. It looks like you are using a multi-out transformer? If so, got a model number? I've been looking for something like that for a while.

I'm using a center-tapped toroidial transformer, Digikey p/n TE62063-ND. I can't remember if that was the exact one from the MB-808 or not...I think it uses the 18V version, this is the 15V version. As I mentioned earlier in the thread, I basically ripped off the MB-808 PSU circuit and tweaked it for ease of construction. Hence the capacitor overkill...just wanted to limit the different types to buy.

I may put heat sinks on the +/- 12V regs...I'll just have to see how they fare heat-wise. The switching reg for the 5V side should be OK.

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I'm using a center-tapped toroidial transformer, Digikey p/n TE62063-ND. I can't remember if that was the exact one from the MB-808 or not...I think it uses the 18V version, this is the 15V version. As I mentioned earlier in the thread, I basically ripped off the MB-808 PSU circuit and tweaked it for ease of construction. Hence the capacitor overkill...just wanted to limit the different types to buy.

I may put heat sinks on the +/- 12V regs...I'll just have to see how they fare heat-wise. The switching reg for the 5V side should be OK.

I can't say if it will be enough, but heatsinks will make a substantial difference. It doesn't take much for regulators to get super hot without one which can be understandable since all the extra heat is only being radiated out a relative small metal tab compared to the size of even a small TO-220 heatsink.

I was able to reign in heat from my first MB-6582 PSU by using just power resistors and heatsinks on everything and things were actually pretty stable.

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  • 7 months later...

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