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LM723 Based Power Supply

On a sunny day (Wed, 20 Oct 2010 16:31:13 GMT) it happened Hammy wrote in :

But my SEPIC can:

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well at least to 24 V, with a bit more input, say 18V it could do 30 I think.

Yes, nice.

There actually is an other way, back in the sixties I did a linear regulator with a thyristor pre-regulator. That pre-regulator just kept about 5V over the series transistor at all times. So dissipation was always rather low. Very simple circuit, one UJT, about 5 transistors, had current foldback too.

Reply to
Jan Panteltje
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Jan Panteltje wrote in news:i9n5u3$n9a$ snipped-for-privacy@news.albasani.net:

Nice project. What is the ripple like?

I see your bench is nice and clean just like mine.;-)

That is the ideal minimze the Vi-Vout difference.The only thing is you still need that big 50/60Hz transformer. They get really big and expensive once you get into the 500VA range for say a 300W output.

I've been noticing a lot of the newer variable output benchtop supplies are now SMPS. I'm guessing they just use the SMPS as a tracking pre-regulator feed that to an opamp based linear regulator.

Reply to
Hammy

On a sunny day (Wed, 20 Oct 2010 19:20:28 GMT) it happened Hammy wrote in :

Feed it into a SEPIC?

Reply to
Jan Panteltje

rnal-september.org:

Yep, a MJ15001 would do the job with one pass element.

2N3055: four for $8; MJ15001: two for $8

Also, to get a low-voltage output (2V at 2.5A) your drive requirement on that high-side pass PMOS transistor would require a negative power supply (-10V to be safe) in addition to the positive one. To use an NMOS, your 30V output would require drive power 40V or so.

Reply to
whit3rd

innews:i9mv68$udl$ snipped-for-privacy@news.eternal-september.org:

What if you have hundreds of surplus 2N3055 you got for nothing?

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Politicians should only get paid if the budget is balanced, and there is
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Reply to
Michael A. Terrell

innews:i9mv68$udl$ snipped-for-privacy@news.eternal-september.org:

I don't have "hundreds" but I have a few that I've had forever ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

               I can see November from my house :-)
Reply to
Jim Thompson

whit3rd wrote in news:1c8a2acd-cb63-4462-9036-bbae582f9ba3 @n13g2000vbn.googlegroups.co m:

@g13g2000yqj.googlegroup

How so? The gate voltage is derived from the input voltage not the output. The drain is connected to the load.

You will need a negative voltage anyways though if you want to get down to 0V other then into a short.

I did some more looking their are some P-FETS at digikey in 300W or greater packages at $4.

Charge pump IC's are cheap you can even use a 555 timer. Granted its a few more components but it will give better performance and will give you a much wider selection in pass devices. I think their are even some integrated highside N-FET LDO controllers out their that can be used.

Reply to
Hammy

innews:i9mv68$udl$ snipped-for-privacy@news.eternal-september.org:

Not all are marked 2N3055 but I've scrapped a lot of linear power supplies with really odd form factors, or very high currents. Mostly from old minicomputers. I have seen whole trays of new 2N3055 sell for less than 25 cents each at a hamfest. The guy had over a hundred trays of 100. You could get 10 trays for $150, which was 15 cents each.

--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
Reply to
Michael A. Terrell

Still overpriced. The Hfe drops off so fast as Ic rises that they are at best .... useless. No, wait, they might be useful as heater elements if you have enough drive.

Reply to
who where

Poor baby! I've designed ignition systems (500V NPN's) where Beta was around 3 at 5A, yet got very accurate performance.

Making do with what you have available separates the men from the boys :-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

               I can see November from my house :-)
Reply to
Jim Thompson

ews.eternal-september.org:

s.

e

I've bought a few desk top computer switching power supplies (working) for a dollar each at swap meets. Nowadays, I can get the whole computer P4 (Win xP) for $35. Keyboards are a dollar extra.

-Bill

Reply to
Bill Bowden

The tracking pre-regulator design on the data sheet *will* do the job (p12)

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Reply to
David Eather

innews:i9mv68$udl$ snipped-for-privacy@news.eternal-september.org:

Quite often not wort the dollar. :(

You pay for them? I pick them up for free.

You pay for keyboards? Can you use 150 or so? How about 75 mice?

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Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
Reply to
Michael A. Terrell

Drop off at DC? They aren't useless unless you don't know shit about linear power supplies. There were literally millions of linear power supplies built with 2N3055. A lot of companies made their entire income from the LM723 & 2N3055.

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Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
Reply to
Michael A. Terrell

$ snipped-for-privacy@news.eternal-september.org:

roups.

ld be

ng?

wer

for

rays

The fan was worth the dollar.

?

I pay nowadays if I need one. The keyboard I use is dirty, so I'm debating spending time cleaning the keys, or just throwing it out and buying another one.

-Bill

Reply to
Bill Bowden

innews:i9mv68$udl$ snipped-for-privacy@news.eternal-september.org:

Not when you have 15 bannana boxes full of old power supplies and boxes of used fans.

Keyboards are easy to clean. Stand it against the wall and spray a fine mist of household ammonia or Windex. Bet it stand there a few minutes and spray it again. A few more minutes and spray it with tap water, or even better, use distilled water. Let it air dry oer night and it should be as clean as new. I've done hundreds this way.

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Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
Reply to
Michael A. Terrell

Nahh, PFET is an LDO style thing. Annoying to compensate, but that's just something to do.

Tim

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Reply to
Tim Williams

Scrap iron is doing good these days. ;-)

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams

Iron? These are mostly tinned copper.

--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
Reply to
Michael A. Terrell

Yes, with massive heatsinks covered with huge numbers of 3055's - saw many of them in mainframe pooter stuff. I've done PSU's with them, but rapidly grew tired of the heatsink real estate they consumed.

In relation to the O/P topic - but not a solution - I have one PSU I built with a 723 driving a single PNP TO3 that gives 12A continuous over 2-15V on a heatsink about 6" x4".

Reply to
who where

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