Hi Everybody,
I need to build my own power supply. I need a proven circuit for 0 to
30V DC variable power supply with minimum 2.5 A current output.I thought I had hit on something good here:
But then, I see some comments on this page saying that there could be errors in the circuit.
Could some expert(s) please confirm that this circuit would work fine? (Or point to something better.)
Thanks for your help.
Thanks, Anand
-- So what's the maximum output current?
As mentioned in the comments, the base drive transistor is reversed, the current limit has no fold-back and therefore isn't safe if you have a short circuit or very low impedance load, and you won't be getting the most out of your pass transistor because you're driving your regulator IC and base drive transistor from the same source as the collector of your pass transistor.
I'd suggest you get a copy of the ARRL handbook, which has a number of power supply designs presented along with explanations of _why_ things are done the way they're done.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
The datasheet has some example designs that can give you a place to start.
-- Rich Webb Norfolk, VA
Fold-back can be very tricky to implement and keep stable _and_ get reliable start-up.
I prefer thermal or current-limit-induced snap-off, requiring a reset.
I don't know why people insist on using such crap as the 723, when you can do much better with a TL431 and a few discrete transistors. ...Jim Thompson
--
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I can see November from my house :-)
IIRC there is also an LM350. Much easier but it won't go below 1.25V. Another problem is power dissipation. You probably need some circuitry to switch the secondary transformer turns.
-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
Probably because of all the circuits out there based on the 723, and the seductive power of a "one chip does all" application (never mind that it's a "one chip does all in a mediocre way")
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
The 723 does have a buried-zener reference, though, so it's probably a lot quieter than a TL431. I might have to switch to that as a jellybean quiet reference if the LM329 goes away!
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs (atsign) electrooptical (period) net http://electrooptical.net
If it needs to be 'proven', you need to BUY, not build.
30VDC output means at least 33V input, and at low-voltage that puts out 33V x 2.5A =3D 82W, which means a single inexpensive transistor isn't gonna handle the output.There's a half dozen tricks that will help: the input power can be transformer-tap-selected to lower the waste, or the pass transistors can be substituted with regulator ICs (which have inbuilt thermal limiting and won't burn up), or you can use two regulators with different voltage ranges, and diode-isolate so they share the output pin.
The easiest thing to do, though, is just to make a brute-force DC power supply, and plug it into a Variac when you want to adjust it. That works, it's efficient, and the Variac (variable autotransformer) comes in handy for lots of other things.
You might try the LM338K adjustable regulator, 5 Amp, built in thermal and current limiting. Adjusts from 1.2 to 30 volts with a few parts -
4 caps, 1 resistor and pot, bridge rectifier, and the 338 on a 100 watt heatsink.-Bill
Even with an infinite heatsink, this part cannot (there's a graph in the data sheet) manage 2.5A if the in/out difference gets as high as 25V. Reference accuracy is only about +/- 5% over temperature, if that matters (the uA723 is better).
Have a look at
Several power suppplies there.
-- ------------------------------------------------------------------ Richard Torrens. News email address is valid - for a limited time only. http://www.Torrens.org.uk for genealogy, natural history, wild food, walks, cats and more!
whit3rd wrote in news:604e1c03-7fe6-4ba7-a59d- snipped-for-privacy@e14g2000yqe.googlegroups.co m:
For such small power pretty well any cheap bjt or fet in say a to247,TO-3PN or ISOPLUS247 is fine you'll need two maybe three for the pass device. Notice I didnt say T0-3 and similiar because heatsinks are more widely avilable for the other packages. A $20 or less heatsink should be good enough.Mount them on something like this
I was easily dissapateing 120W useing two T0-3PN fets on a heatsink from a microwave oven with a $5 42CFM fan. The case temp was at about 90C.The heatsink was less then half the size of the one in the link.
The only time you are going to dissapate 82W would be in the event of catastophic failure. The 723 has foldback protection if it fails the supply should be fused anyway.
A 160VA or better variac is pretty pricey though and bulky, they are definetly useful though.
The tracking pre-regulator design on the data sheet might (p12)
And how much can a 2N3055 dissipate in the same TO-3 package with an infinite heatsink? Probably depends on ambient temp? You could use a center tapped xformer to select either full or half voltage input to reduce heat. There should be some 12VAC (17 volt peak) battery charger transformers using the SCR idea. I think they use a center taped transformer so they only need 2 diodes. If you use a bridge and a switch, you can select 17 volts peak or 34, which should be about right for an adjustable 30 volt supply. Maybe DigiKey has something that would work with a center tap?
-Bill
Enough power (spec sheet says 115W), but the safe-operating-area limit for continuous 2.5A output is only 20V, at 25 C (i.e. with infinite heat sink in a warm room). That's called the 'second-breakdown' limit.
It's a good, cheap transistor, but it'll take several in parallel to do this job, and/or a series transistor to take some of the voltage-drop burden.
A laughable claim!
At least use MJ15001 for starters. 2N3055 is old and should be forgotten.
Tim
-- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
"Tim Williams" wrote in news:i9mv68$udl$ snipped-for-privacy@news.eternal-september.org:
Whats wrong with a P-FET. $8 AT Digikey 3 pages of 300W plus pacakages to choose from.
IXYS makes a linear line of fets too,nice. ;-)
The next high power regulator I make is going to be N-FETS for the pass device; much larger selection, cheaper heatsinks with a larger selection and no stability concerns at least compared to a PFET or PNP.
On a sunny day (Wed, 20 Oct 2010 16:04:19 GMT) it happened Hammy wrote in :
Has anybody mentioned switchers in this thread? Seems so much 'cooler'.
Jan Panteltje wrote in news:i9n445$khl$ snipped-for-privacy@news.albasani.net:
[snip]He wants 0-30 out I've seen variable output flybacks in that power range but they cant vary that widely.
This one here is 18-24V @85W out.
You could use an SMPS on the front end to step down the line voltge. That way you can save the size and expense of a 50/60Hz transformer. Then just use an op-amp based regulator driving a fet pass device on a brick heatsink for your variable output.
Given the size of some of the higher power 300W plus benchtop power supplies today they have to be SMPS's at least the front end.
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