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Russ White 2nd September 2009 02:54 AM

Placid-BP Bipolar Shunt Regulated Power Supply
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Hey Folks,

Here is the Placid-BP under test.

Just wanted you to see that the new boards are here and they are tested. It is working perfectly. I have it set up to drive both sides of a BUF32S at 15V rails.

It is very easy to calculate fixed Rs to set the standing current and output voltage, but you can also use pots and make it adjustable. Fixed Rs are just a bit less noisy if you know what you are aiming for already.

My calculations proved very close, I ended up with +14.94 and -14.75V. Not too bad. :)

I sounds great, and is nice and stable.

There are two green LEDs per rail that set the reference voltage. Those can be replaced with other references if you need, but the LEDs are a very low noise reference. It would be hard to do any better.

There is also an RC filter prior to the opamp which drives the CFP shunt.

The shunt employs a shaped compensation scheme that keeps the regulator stable even into large capacitances (I have tested 1000uf low ESR Pannasonc FMs). You typiclaly do not want to load a shunt reg with a very high capacitance. It defeats the purpose.

The CCS and Shunt transistors are situated so that they can be mounted directly to a suitable chassis where vertical space is at a premium.

More details to come shortly. I have two more new circuits to test. :)


TheShaman 2nd September 2009 07:02 AM

Good job, Russ. :cheers:
An objective and subjective comparison to LCBPS would be appreciated! :D

Beefy 2nd September 2009 12:22 PM

They look like pretty tall heatsinks! Here's hoping I can get away with the regular 1 inch ones to allow for easy stacking......

BrianDonegan 2nd September 2009 02:01 PM

1-inch heatsinks will work in many situations. The kits will ship with 1.5" heatsinks to allow more flexibility. There will be times when you may need something larger (2" or chassis). Shunts generate heat. Stacking may or may not be a good idea, depending on what you want to do, and the case you are using.

Beefy 2nd September 2009 02:12 PM

I was thinking along the lines of dual mono supplies for Buffalo. I'll just wait for more info to come out before I make any decisions......

tailspn 4th September 2009 09:52 PM

Hi Russ,

I have need for a bipolar +/- 24V supply at 500MA. Can a Placid with adequate heat sinking accommodate that need? The current is fairly static. If required, I would parallel the pass transistors, say with hard wires and low value sharing resistors. I anticipate using a forced air cooled tunnel heatsink.


Beefy 4th September 2009 10:28 PM

Obviously I'm not sure whether Placid could handle it...... but if it can't then the Sigma22 is a perfect option; assuming it fits in your case, no modifications would be necessary.

tailspn 5th September 2009 12:18 AM

Thanks Beefy. Unfortunately the Sigma 22 is not a shunt regulated power supply. There's no problem finding series regulated supplies to fit my power needs, and I've built a bunch of them, including the Sigma 22. There's even a great thread here on DIY about optimizing the 317/337 that looks very interesting:

Thanks again,

Beefy 5th September 2009 01:24 AM

And the practical difference is.........?

I've read a little bit on shunt versus series, and from what I can see they are basically just two different sides of the same coin.

tailspn 5th September 2009 02:06 AM

Actually not. It's all about supply impedance symmetry. A series regulator turns on more to supply current to a dropping load voltage caused by the load drawing more current. However, when the load voltage is rising, caused by its drawing less current, the series regulator delivers less current, but it's the load that has to absorb the excess energy. That's OK as long as the load can absorb the excess faster than it can be reduced. Otherwise, the voltage at the load rises. In effect, the output voltage of a series regulator only regulates in one direction, ie, when the load is asking for more current. In the other direction, the regulator is coasting.

A shunt regulator regulates in both directions, both by supplying more current, and absorbing excess current from the load. the effect is a much more constant source impedance as seen by the load.

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