Hi from a new mamber. Retired, and now have time for a hobby.
first up, im looking to build a power supply. while I am comfortable following a schematic and know what the components are,
will it work or not is another issue. I found this schematic on line and would like to ask if it will work, or go pop?



If I remember right, this puppy is suposed to pump out 1.5 - 37 Volt at a max of 30 Amps. (Why not 0 - 37?)
Now I can understand the 6 x 317s for the heat dispersion, would it be any better to have say 8 x 317s

Also I would like to have the ability to adjustable current, would be greatful if anyone could assist me in this regard.
I also have a display to show volt and amp output.
I intend to have two or 3 outputs, each being adjustablein its own right, I do understand the total current can only be up to the maximum of the unit, 30 Amp in this case.

The transformer for this I pulled of an old microwave and rewound it, got a good output that tests as 12.8 volt, with another winding that gives 5 volt for a cooling fan.

Thanks in advanc

 

hi pappy,
Welcome to AAC.
Are you sure that you copied the circuit diagram correctly from the web.?
E

 

That circuit definitely looks odd. I doubt whether it was ever tested as shown in the diagram. With a 40 volt secondary winding on the transformer, there will be about 55 volts DC across the regulators. The LM317 absolute maximum voltage rating is 40 volts. Proceed with caution.
Regards,
Keith

 

Welcome to AAC!

I wouldn't trust circuits from people who resort to drawing them as cartoons.

If I remember right, this puppy is suposed to pump out 1.5 - 37 Volt at a max of 30 Amps. (Why not 0 - 37?)
Now I can understand the 6 x 317s for the heat dispersion, would it be any better to have say 8 x 317s

It can't go to 0V because it's using LM317 which would require a negative supply to get to 0V and is usually an unnecessary complication.

The unlabeled (another sign of an amateur) green thingies along the top aren't voltage regulators, they're power transistors.

The power transistors should be on the same heat sink as the regulator so its safe area protection circuitry can protect them. Personally, I'd put the fuse on the input side of the regulator so it's resistance won't affect voltage regulation.

Do you really need 30A? None of my power supplies will source more than 3A and I rarely use that much. I'm more likely to use wall warts and USB chargers to power circuits - YMMV.

The transformer for this I pulled of an old microwave and rewound it, got a good output that tests as 12.8 volt,

That will limit your maximum output voltage to around 15V.

EDIT: One other thing... The current set resistor is 240 ohms, which will give a minimum load current of 5mA. The datasheet specifies a minimum of 10mA for proper operation. It will work with less (I often use 274 ohms and add a load if necessary), but it's not something I'd do without adding a note about it or adding an LED indicator to get the minimum up to 10mA.

 

Hello,

The top devices are likely PNP transistors.
Have a look at this schematic, there is a PNP pass transistor:



If you want a beefier regulator, have a look at the LT1083.
That is capable of 7.5 A.

Bertus

 

hi pappy,
Welcome to AAC.
Are you sure that you copied the circuit diagram correctly from the web.?
E

Yep, copy and saved the immage.
If this schematic is a fake, would you or anyone know of a working one I could look at?

 

If this schematic is a fake

It's real, but poorly drawn and designed.

A couple circuits from the National Semiconductor datasheet:

 

hi p,
That circuit will not give the results you are expecting.
As others have said , what voltage output range and current drive would be an acceptable value for the design.?
E

 

Welcome to AAC!

I wouldn't trust circuits from people who resort to drawing them as cartoons.
It can't go to 0V because it's using LM317 which would require a negative supply to get to 0V and is usually an unnecessary complication.

The unlabeled (another sign of an amateur) green thingies along the top aren't voltage regulators, they're power transistors.

The power transistors should be on the same heat sink as the regulator so its safe area protection circuitry can protect them. Personally, I'd put the fuse on the input side of the regulator so it's resistance won't affect voltage regulation.

Do you really need 30A? None of my power supplies will source more than 3A and I rarely use that much. I'm more likely to use wall warts and USB chargers to power circuits - YMMV.

That will limit your maximum output voltage to around 15V.

EDIT: One other thing... The current set resistor is 240 ohms, which will give a minimum load current of 5mA. The datasheet specifies a minimum of 10mA for proper operation. It will work with less (I often use 274 ohms and add a load if necessary), but it's not something I'd do without adding a note about it or adding an LED indicator to get the minimum up to 10mA.

You are right, probably woul never use 30A, I guess I was thinking along the lines of 'never going to push it that high, so it should last longer'

 

I guess I was thinking along the lines of 'never going to push it that high, so it should last longer'

A more important consideration is whether you'll be operating it at a low output voltage and high current.

If you don't use more than 3A, an LM337 is a single chip solution (no need for external power transistors).

 

hi p,
That circuit will not give the results you are expecting.
As others have said , what voltage output range and current drive would be an acceptable value for the design.?
E

I was thinking of up to 30 volt, and around 10 Amp would be ample for anything I was going to start with

 

I was thinking of up to 30 volt, and around 10 Amp would be ample for anything I was going to start with

The voltage regulator and rectifier will drop 3-4 volts, so you'll need a 24VAC secondary.

 

Welcome to AAC!

I wouldn't trust circuits from people who resort to drawing them as cartoons.
It can't go to 0V because it's using LM317 which would require a negative supply to get to 0V and is usually an unnecessary complication.

The unlabeled (another sign of an amateur) green thingies along the top aren't voltage regulators, they're power transistors.

The power transistors should be on the same heat sink as the regulator so its safe area protection circuitry can protect them. Personally, I'd put the fuse on the input side of the regulator so it's resistance won't affect voltage regulation.

Do you really need 30A? None of my power supplies will source more than 3A and I rarely use that much. I'm more likely to use wall warts and USB chargers to power circuits - YMMV.

That will limit your maximum output voltage to around 15V.

EDIT: One other thing... The current set resistor is 240 ohms, which will give a minimum load current of 5mA. The datasheet specifies a minimum of 10mA for proper operation. It will work with less (I often use 274 ohms and add a load if necessary), but it's not something I'd do without adding a note about it or adding an LED indicator to get the minimum up to 10mA.

Ok, my first mistake on the transformer, work on rewinding that in the morning. what would be the best voltage to have in this regard, (based on a 30v max output.)

 

hi p,
That circuit will not give the results you are expecting.
As others have said , what voltage output range and current drive would be an acceptable value for the design.?
E

I was thinking of up to 30 volt, and around 10 Amp would be ample for anything I was going to start with

 

what would be the best voltage to have in this regard, (based on a 30v max output.)

24VAC

Something you should consider is how much current you'll be drawing at low voltage. If your main purpose will be a 5V supply, this design would be very inefficient and you should use a switching power supply instead. The LM317 datasheet should have examples of how to use it as a switching regulator.

Another thing you need to consider is the secondary current. To get 10A at the output, you'll need a higher secondary current.

 

Here's some information on transformer current requirements based on rectifier circuit.

 

I wouldn't bother making one when you can get a decent 30v 10a switching one for £46. Just ordered this, it's very small and gets good reviews, also good video reviews on you tube.

[£45.84 38% OFF]LONG WEI® LW-K3010D 110V/220V 0-10A 0-30V Adjustable DC Power Supply Regulated Digital Laboratory Maintenance Switching Power Supply Electrical Equipment & Supplies from Tools, Industrial & Scientific on banggood.com
https://banggood.app.link/0PUG3JEh55

 

What projects that you have in mind would require such a high current?

 

I was looking at the 5 amp ones on ebay as that would be plenty, the one I've got now is 1 amp. But when I looked them up on Bang good the 10 amp ones were cheaper

 

Bang good the 10 amp ones were cheaper

I wouldn't buy a power supply from Banggood, AliExpress, Amazon, or the like. Cheaper usually means lower quality.