bipolar power supply using positive regulators only ?

[PHOBoS]

I was looking for some adjustable voltage regulators that are a bit beefier than the standard LM317/LM337.
I came across the LT1083 which is available for 3A, 5A, 7.5A and also seems to have some better specs than the LM317.
There is a negative version: the LT1033, but it is discontinued. I did however find some dual supplies on ebay which use
2x LT1083 and in the description it says they can be put in parallel for more current, in series for a higher voltage but also
for a bipolar supply. Searching a bit more I came across some other places where it was mentioned that you can put 2 regulated
positive supplies in series to create a bipolar supply. One example is this one
.


I am pretty sure it will work but it does seem a bit odd and I wonder if not having a single GND bus straight to the supply
can cause any problems. So, are there any downsides to this method ?
(Note: this can not be used with a center tapped transformer)

[blue hell]

You'll see this construction every now and then ... actually I did have a PSU built this way in the past .. it worked pretty well even.

And indeed you need a dual wounded secondary.

[Skrog Productions]

Hi Phobos

i was thinking of refreshing my substation power supply for the blue modular sometime and i was browsing some circuits to use with my 225VA dual secondary toroidal transformer one that caught my eye was this one using the oval shaped 5A LM338 regs , i have 2 supplies needed +/- 12V and +/- 15V , the biggest load , on my current supply just now is on the 12V side , drawing 2A on + / 1.6A on - .

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[Skrog Productions]

oooopps , forgot the little circuit you showed me a while back for coupling mains earth to the 0V tie point .......

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[PHOBoS]

Well, I guess I shouldn't have any concerns than

I always like the look and feel of the TO-3 package, it's a bit more work to mount on a heatsink though.
btw. 3x 15000uF per rail is quite a lot, might cost you some fuses when turning it on and the light will
dim of course (in the whole neighbourhood). Do you have that knife switch installed yet ?

[piedwagtail]

I'm quite fond of the LM350.

I renovated a 30V 30V bench supply with those, which is of course two identical circuits, stacked in use to resemble your design.

Also used them as current regulators inline.

R

[PHOBoS]

The LM350 looks like a nice one too for some more power. Not enough for what I have in mind though but it might come in useful someday.

[PHOBoS]

[JovianPyx]

I remember a discussion on SDIY about this. In the end, it works well enough for most applications (if not all). The discussion seemed to concentrate on the fact that when you use a negative regulator for the negative voltage, the regulator's ground connection is connected to the circuit's ground (and same with the positive regulator). When a positive regulator is used to make a negative voltage, it's output pin is connected to circuit ground and the ground pin connects to the negative voltage. It works because all the regulator cares about is the voltage at the output pin with respect to the chip's ground pin.

I've done this a couple of times with good results. I do prefer to use a negative regulator for negative supply, but that's more just because it "feels" better than anything empirical.

[PHOBoS]

Thanks scott, good to have some more confirmation and yeah I just doesn't feel totally right eventhough it should work fine.

[Skrog Productions]

ahh , so the small earth circuit is not of any benefit , i never got round to trying one on my system yet .

200Amp knife switch is ordered , lol .

Yes i agree about the drop from 19V to 12V produces sausage sizzling heat with 1 set of regs ,been there ,singe , tho my existing system like your existing system has the supply from the bridges go to several sets of regs doing their own bus bars, this also stopped the weird vco tune movement i had ages ago and stopped when the 6 vcos got their own regulators & busbar .

Yes thats a lot of big caps in the circuit , this circuit could well have come from hiFi amp design area , not sure , for my set up 10000uF would suffice

[piedwagtail]