Bench Power Supply

[SuperSpit]

Hi everyone.

My first post here for a while.

I was wondering if I could get some help from you guys?

I'm really wanting to build a half-decent power supply. I have experience with how the simple voltage regulators work, but that is where my knowledge of power supplies wanes.

I have tried looking for a well documented project on the internet, but I cannot seem to find anything. Every project contains out of date, or hard to find components, with no clue as to where to find them.

I'm not too fussy when it comes to specs. A few amps and I don't think I'll ever need more than 20V output. An LCD display would be nice, but not vital.

I don't mind if it uC based, or voltage regulator based, or op amp based... Just so long as there is decent information about it.

I'm probably going to have to give you guys some more information, please feel free to ask.

I thank you all for your time.

Spit

 

[ronv]

One key to sucess is a good spec to start with. So lets try one out.

How about 1.25 volts to 20 volts at 1 amp.
Short circuit protected.
Small LED read out.

This would be pretty easy.

But lets say you want:

0 to 20 volts at 2 amps

Adjustable current limit.

This would be more difficult and more expensive

 

[SuperSpit]

How about 1.25 volts to 20 volts at 1 amp.
Short circuit protected.
Small LED read out.

That sounds fantastic.

May I add voltmeter and ammeter read out. (LED)
240VAC input.

Thanks very much!

 

[ronv]

Sure, Do you have a place where you buy parts? I'm guessing you are not in the US so I hate to send you to Radio Shack for parts when you don't have one.

 

[SuperSpit]

Yes, I can get them from Farnell, they tend to have a very good range of supplies.

They also do free next day delivery on all orders, which is nice. I think they are called Newark in the US.

 

[ronv]

Here is a transformer (I think it has 115 or 230 v input) and 2X20 volt output so we can use centertaped full wave rectifiers.

https://uk.farnell.com/pro-power/ctfc75-20/transformer-75va-2-x-20v/dp/1780862

I'll draw up the bulk supply and we can start from there if the price looks ok to you.

 

[SuperSpit]

That looks fantastic! Thanks very much Ron.

 

[ronv]

OK. Here is the bulk supply. It will give you about 25 volts to send to the regulator. I have to go for a while, but will add the regulator part later. The diodes are rated at 3 amps and the cap at 50 volts. We just need to add the regulator and find some little meters for the voltage and current. Can you read schematics okay?

 

[SuperSpit]

That looks great.

Yeah, I can read schematics pretty well.

I'm trying to make the jump from having just a regulator, to supplies with power transformers and other goodies.

 

[atferrari]

Sure, Do you have a place where you buy parts? I'm guessing you are not in the US so I hate to send you to Radio Shack for parts when you don't have one.

Do you still send people to buy parts from RS if they have one close?

 

[ronv]

No, I'm a Mouser fan, but Radio Shack has some bargains on 24 volt 2 amp transformers for $10 and they have ferric chloride. Other than that I only use them when I can't wait for shipping.

Super, Here is a pretty good heat sink that should do the job.

https://uk.farnell.com/fischer-elektronik/sk-64-75-sa-2-xm-3/heat-sink-to-220/dp/4621542

 

[ronv]

OK lets have a look at this.
I'm thinking some little digital meters from China that you can find on Ebay. I saw a 0 -5 amp and a 0 -30 volt one pretty cheap.

 

[Mr RB]

I hope you don't mind if I suggest some changes to that schematic Ron?

The resistor R2 120 ohm should be between Out and Adj pins of the LM317, to ensure the 10mA output current.
C3 should be between Adj pin to ground to ensure stability.

Also as a suggestion a second LM317 can be added before the voltage regulator LM317, as an adjustable current limiter(using a resistor, or some switched resistors). It can be switched out of circuit too if needed by shorting it out with a switch.

 

[fernando_g]

My two yen:
In addItion to the variable output, have a second fixed output @ 5V.
That is an ubiquitous voltage in digital projects, frees up your other output for other circuits, and can be cheaply added with a 7805 and heatsink.

 

[ronv]

I hope you don't mind if I suggest some changes to that schematic Ron?

The resistor R2 120 ohm should be between Out and Adj pins of the LM317, to ensure the 10mA output current.
C3 should be between Adj pin to ground to ensure stability.

No, no problem. That's how it should work. I'm a little .

Also as a suggestion a second LM317 can be added before the voltage regulator LM317, as an adjustable current limiter(using a resistor, or some switched resistors). It can be switched out of circuit too if needed by shorting it out with a switch.

I like the idea but we would need a higher bulk supply (transformer) to support the 20 volts at low line i think.
But we could look for a 24 volt transformer.

The 5 volt supply is another nice touch. I have that on my supply. If you would like that just add a 7405 like the 7412 is shown. Let us know if you like the adjustable current limit and we can look for a different transformer.

Here is the new schematic.

 

[k7elp60]

Here is a schematic and a parts list for a dual power supply I designed and built recently. It is 0-15 both + and - dual tracking with short circuit current limiting to about 400Ma. To change to 0-20V resistors R10, and R11 need to be changed to 300K 1% 1/4W and to increase the current limit to 1A change resistors R7 and R8 to 0.68Ω 2W.
The physical size of the two heat sinks needs to be increased.
The dual power supplys near the bottom were used as I used some LED DVM's for monitoring the voltage and the current...they required isolated supplies.

 

[k7elp60]

Moderator I have tried to post a pdf file but I keep getting a error message that I am not allowed to post attactements. Whats wrong.
k7elp60

 

[ronv]

Try posting it as a .png file

 

[Mr RB]

... The 5 volt supply is another nice touch. I have that on my supply. If you would like that just add a 7405...

I agree, it's great having a safe reliable 5v supply without having to fiddle with voltage adjustment.

A little 78L05 has a 100mA current limit built in, which is easy to use.

But in my favorite supply I use a LM317 with a centre-off SPDT switch and 3 resistors to set 3 current limits; 20/50/100 mA which I find are perfect for small digital work, then that is followed by a typical 7805.

 

[Ian Rogers]

Moderator I have tried to post a pdf file but I keep getting a error message that I am not allowed to post attactements. Whats wrong.
k7elp60

Some parts of the forum are still broken... The Administrator is working to fix ALL the issues.... Try other mediums... JPG and PNG are ok.. I think GIF and PDF are still a problem.