Power Supply

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When working with electronics, you always need one basic thing; power. This power supply is great for powering all kinds of electronic projects. It produces a well filtered, variable 1.2-30 volts at 5 amps. It is easy to build and the parts are realitively easy to find.

Schematic

Parts

Part	Total Qty.	Description	Substitutions
C1	1	14000uF or 10000uf 40 VDC Electrolytic Capacitor
C2	1	100uF 50Vdc Electrolytic Capacitor
C3	1	0.1uF Disc Capacitor
C4	1	0.01uF Disc Capacitor
R1	1	5K Pot
R2	1	240 Ohm 1/4 W Resistor	See Notes
U1	1	LM338K 1.2 to 30 Volt 5 Amp Regulator
BR1	1	10 Amp 50 PIV Bridge Rectifier
T1	1	24 V 5 Amp Transformer
S1	1	SPST Toggle Switch
MISC	1	Wire, Line Cord, Case, Binding Posts (for output)

Notes

The regulator comes in a TO-3 case and MUST be used with a LARGE heatsink. You may want to mount a small fan to blow air across the regulator (I did).

The filter capacitor is large. It won't fit on any board so bolt it to the case.

You can, of course, add a volt and amp meter.

Since this project operates from 120 VAC, you must include a fuse and build the project in a case.

R2 may need to be decreased to 120 Ohm if you experience voltage drift at light loads. 240 Ohm may not load the output appropriately on some regulators. The datasheet for the LM338K does specify 120 Ohm (I suggest you use a 1/2W unit) so you may just want to use 120 Ohm and not bother with the 240 Ohm resistor showin the parts list. This has been discussed on the forum.

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Comments

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Adam Kellerson Power Supply Sunday, June 20, 2010 6:55:42 PM

More a curiosity question than anything. The LM338 schematic shows an input voltage of greater than 28V while you have a transformer outputting 24v spec'd out. (assuming 120Vac input) ?

Tom Power Supply Sunday, February 14, 2010 11:47:34 PM

I have a couple 13.8 vdc power supplies that were used for ham radio; I'd like to build an aux. project box to use as a 1.2 to 12 vdc, 5A Variable Power Supply. If I include everything to the right of the bridge rectifier in the above circuit, am I on the right track? ... Thank you very much for your reply!

Mike Tanner Power Supply Wednesday, January 20, 2010 6:12:41 AM

Hi Aarron What pin on the 2n3005 is the IN, OUT and ADJ. The data sheet for the 2n3055 does not give this kind of info. Am I to assume that the IN is the Collector, the OUT is the emitter, and the ADJ is the base. I have tried to wire this up but it is not working. I may have burn something up or have it wired up wrong. Thanks Mike

ilyas Power Supply Tuesday, September 15, 2009 8:05:30 AM

i cant find the exact valued elements for this circuit and pruchased a 24 V, 3Ampere transformer, 270 Ohm, 4.7 K Pot, 100uF 63Vdc Electrolytic Capacitor, 8200 uf 50 VDC Electrolytic Capacitor. actually i want 3 ampee cureent and variable 2 to 20 volts. with these element what output is expected ? Sir, please tell me ASAP.

peterlonz Power Supply Friday, September 04, 2009 12:55:33 AM

Nice but based on fairly costly linear regulator. With variable output power supplies it's important to easily get the output regulated voltage that you need at any particular time. My thoughts on this is either: 1) Permanently hook up a cheap digi multimeter so that setting the output is easy & accurate, or 2) Building in a panel digi voltmeter. I'd prefer this but do not have access to a low cost design. Can anyone help here

George Power Supply Wednesday, July 22, 2009 12:38:39 AM

Looking to build a power supply for a foam hot wire cutter, wire will be 12 to 36 inchs long depending on project. Would this power supply work for this? I would like to have 24 v and anywhere from 5 to 10 amps, so that is what caught my attention to this power supply. Thanks Great site.
(Editor's notes: No.)

anonymous Power Supply Sunday, July 19, 2009 11:22:18 PM

Nonsence. This will not supply 5 amps with a Voltage differential from input to output of 30 Volts. At 30 Volts between input and output and 5 amps out you will be dissipation 150 Watts in the device and it will go into shutdown. It can only supply one amp when Voltage between input and output is 30 Volts. See data sheet page three at bottom. Sorry about that
(Editor's notes: Not true. I've used this very supply for years. No issues dumping 5A into a 24V battery.)

babu Power Supply Tuesday, July 14, 2009 12:38:50 AM

sir good morning. i want to know basics of power supply how it works? i don't have any idea about it so please send me some materials of power supplies basics, types of power supplies,applications. in net everything is available but it is vast and unable to understand practically.so please help me as soon as possible .its very urgent.

Twan Power Supply Friday, July 10, 2009 5:22:04 PM

I have been searching for a design that has a 120 vac input and a 30 vdc output @ 15 amps. Have you designed anything like that so far? If not, I would appreciate any advice if not your own design. THANKS

RLC Power Supply Saturday, April 25, 2009 1:59:14 AM

hi sir it's good power supply ckt, but i don't want to use transformer so please send me ckt that should not contain transformer but do the same operation as this ckt do.
(Editor's notes: You need a transformer.)

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Adam Kellerson	Power Supply	Sunday, June 20, 2010 6:55:42 PM
More a curiosity question than anything. The LM338 schematic shows an input voltage of greater than 28V while you have a transformer outputting 24v spec'd out. (assuming 120Vac input) ?
Tom	Power Supply	Sunday, February 14, 2010 11:47:34 PM
I have a couple 13.8 vdc power supplies that were used for ham radio; I'd like to build an aux. project box to use as a 1.2 to 12 vdc, 5A Variable Power Supply. If I include everything to the right of the bridge rectifier in the above circuit, am I on the right track? ... Thank you very much for your reply!
Mike Tanner	Power Supply	Wednesday, January 20, 2010 6:12:41 AM
Hi Aarron What pin on the 2n3005 is the IN, OUT and ADJ. The data sheet for the 2n3055 does not give this kind of info. Am I to assume that the IN is the Collector, the OUT is the emitter, and the ADJ is the base. I have tried to wire this up but it is not working. I may have burn something up or have it wired up wrong. Thanks Mike
ilyas	Power Supply	Tuesday, September 15, 2009 8:05:30 AM
i cant find the exact valued elements for this circuit and pruchased a 24 V, 3Ampere transformer, 270 Ohm, 4.7 K Pot, 100uF 63Vdc Electrolytic Capacitor, 8200 uf 50 VDC Electrolytic Capacitor. actually i want 3 ampee cureent and variable 2 to 20 volts. with these element what output is expected ? Sir, please tell me ASAP.
peterlonz	Power Supply	Friday, September 04, 2009 12:55:33 AM
Nice but based on fairly costly linear regulator. With variable output power supplies it's important to easily get the output regulated voltage that you need at any particular time. My thoughts on this is either: 1) Permanently hook up a cheap digi multimeter so that setting the output is easy & accurate, or 2) Building in a panel digi voltmeter. I'd prefer this but do not have access to a low cost design. Can anyone help here
George	Power Supply	Wednesday, July 22, 2009 12:38:39 AM
Looking to build a power supply for a foam hot wire cutter, wire will be 12 to 36 inchs long depending on project. Would this power supply work for this? I would like to have 24 v and anywhere from 5 to 10 amps, so that is what caught my attention to this power supply. Thanks Great site. (Editor's notes: No.)
anonymous	Power Supply	Sunday, July 19, 2009 11:22:18 PM
Nonsence. This will not supply 5 amps with a Voltage differential from input to output of 30 Volts. At 30 Volts between input and output and 5 amps out you will be dissipation 150 Watts in the device and it will go into shutdown. It can only supply one amp when Voltage between input and output is 30 Volts. See data sheet page three at bottom. Sorry about that (Editor's notes: Not true. I've used this very supply for years. No issues dumping 5A into a 24V battery.)
babu	Power Supply	Tuesday, July 14, 2009 12:38:50 AM
sir good morning. i want to know basics of power supply how it works? i don't have any idea about it so please send me some materials of power supplies basics, types of power supplies,applications. in net everything is available but it is vast and unable to understand practically.so please help me as soon as possible .its very urgent.
Twan	Power Supply	Friday, July 10, 2009 5:22:04 PM
I have been searching for a design that has a 120 vac input and a 30 vdc output @ 15 amps. Have you designed anything like that so far? If not, I would appreciate any advice if not your own design. THANKS
RLC	Power Supply	Saturday, April 25, 2009 1:59:14 AM
hi sir it's good power supply ckt, but i don't want to use transformer so please send me ckt that should not contain transformer but do the same operation as this ckt do. (Editor's notes: You need a transformer.)