Author Topic: Help with diy bench psu circuit.  (Read 2774 times)

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Offline gabri.peic

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Re: Help with diy bench psu circuit.
« Reply #25 on: February 02, 2022, 06:48:01 pm »
Would this be alright for just variable voltage?
https://www.electronics-lab.com/project/5a-adjustable-regulated-power-supply/
It would obviously need larger heatsink and i would not use more then around 3A but does the circuit look good for just variable voltage?
 

Offline JohanH

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Re: Help with diy bench psu circuit.
« Reply #26 on: February 02, 2022, 07:05:13 pm »
If you want the cheapest possible this is probably it. Go ahead and build it. Once you have the chassis, meters, connectors and switches in place, it isn't hard to replace the PCB with something more complicated in the future. I would use a larger heat sink mounted to the chassis and possibly use a chassis mount rectifier. The hardest part is probably finding a heat sink that fits your needs. Plan the chassis so that you could add a fan if needed. Then you could easily change the PCB to something else in the future. But that's just my opinion.
 

Online Kleinstein

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Re: Help with diy bench psu circuit.
« Reply #27 on: February 02, 2022, 07:20:08 pm »
The LM338 is likely a relatively expensive solution, but a simple circuit. Because of power limits the regulator likely has a fold back current limiting. So if little voltage is droped the current can be high (like 5 A), but if more voltage is droped the current limit would be lower (like 1.5 or 2 A). This helps to limit the worst case power loss and is still OK to power a circuit running at a relatively high voltage (e.g.   < 10 V drop).

There are a few threads about lab supply circuits - some of them are OK, e.g. one based around LM324 OPs.
 

Offline ledtester

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Re: Help with diy bench psu circuit.
« Reply #28 on: February 02, 2022, 07:24:13 pm »
Basically it looks ok, but I'd compare it with the reference designs in the datasheet:

https://www.ti.com/lit/ds/symlink/lm338.pdf

You might want to add the protection diodes in Figure 18.

Check the ** note in Figure 23 for the value of R2 in the schematic (120R vs 220R).

The LM338 also has a min. load current (< 10mA). You might consider adding some sort of permanent load on the output to satisfy this.

In general the TI datasheet has got a lot of good bits of advice especially with regard to component selection and layout.

« Last Edit: February 02, 2022, 07:26:02 pm by ledtester »
 

Offline gabri.peic

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Re: Help with diy bench psu circuit.
« Reply #29 on: February 02, 2022, 07:34:53 pm »
Ok,thanks. I will think about all the options and choose one.
 

Offline JohanH

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Re: Help with diy bench psu circuit.
« Reply #30 on: February 02, 2022, 08:07:20 pm »

The LM338 also has a min. load current (< 10mA). You might consider adding some sort of permanent load on the output to satisfy this.


I have used a power-on LED  (3mm LED and resistor) with some other regulator to satisfy its minimum load current. Then its not just wasted in a dumb resistor   :)
 

Offline Neomys Sapiens

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Re: Help with diy bench psu circuit.
« Reply #31 on: February 02, 2022, 08:24:43 pm »
I can only warn you that the LM338 can be cooked faster than its thermal protection can act when not mounted on a really good and generous heatsink. Then any retry will waste more money than one of the simpler PS with current limiting would cost you. If using a LM338, my tip would be the circuit with the additional OPA and current limit.
 

Offline gabri.peic

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Re: Help with diy bench psu circuit.
« Reply #32 on: February 02, 2022, 09:25:02 pm »
Thats what worries me. That i will just waste money.
The "30V 3A kit" with modification by audioguru seems like the cheapest somewhat decent circuit.
 

Offline gabri.peic

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Re: Help with diy bench psu circuit.
« Reply #33 on: February 03, 2022, 06:05:14 pm »
So before i start spending money. Will the circuit attached below work alright or not?
I would build the elektor circuit but it is a bit more expensive.
The circuit attached is the chinese kit modified by audioguru.
 


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