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Old 5th Oct 2022, 3:00 pm   #21
Vintage_RC
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Default Re: Homebrew PSU Problems

I purchased a linear PSU kit from Banggood based around the LM317. Performance was weird and erratic. I dug out an old genuine Nat Semi one from the spares box and all the problems vanished.
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Old 5th Oct 2022, 6:02 pm   #22
Electronpusher0
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Default Re: Homebrew PSU Problems

Going back to the question of are they fakes, check the voltage between the adjust pin and output, this should be 1.25V, if it reads about 0.7 then you have been sold a simple transistor and it's working as an emitter follower, this will give a variable output but with no protection.
Just a thought

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Old 5th Oct 2022, 7:26 pm   #23
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Default Re: Homebrew PSU Problems

Quote:
Originally Posted by Electronpusher0 View Post
Going back to the question of are they fakes, check the voltage between the adjust pin and output, this should be 1.25V, if it reads about 0.7 then you have been sold a simple transistor and it's working as an emitter follower, this will give a variable output but with no protection.
Just a thought

Peter
On diode check ? Will do when i get a chance

0.663v on diode check

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Jay
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Last edited by Radio Scotland; 5th Oct 2022 at 7:30 pm. Reason: extra info
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Old 6th Oct 2022, 9:20 am   #24
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Default Re: Homebrew PSU Problems

I actually meant when the regulator is on and working but a diode test of 0.6 certainly looks like you have been sold transistors labeled as regulators, fakes in other words.

Peter
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Old 6th Oct 2022, 9:29 am   #25
kalee20
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Default Re: Homebrew PSU Problems

It would also be of the opposite polarity!

LM317 has its adjustment pin 1.25V -ve to output terminal, whereas an NPN transistor would have the base 0.6 V positive to output terminal (emitter).

I've never had any problems with the LM317 except a bit of noise. And I've used lots - they're one of National Semiconductor's triumphs!
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Old 6th Oct 2022, 10:15 am   #26
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Default Re: Homebrew PSU Problems

Quote:
Originally Posted by Electronpusher0 View Post
I actually meant when the regulator is on and working but a diode test of 0.6 certainly looks like you have been sold transistors labeled as regulators, fakes in other words.

Peter
Wouldn't be the slightest bit surprised, Bought them direct from china a few years ago, I'm actually planning on using the LM338 But they seem to have vanished in the post
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Old 6th Oct 2022, 11:25 am   #27
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Default Re: Homebrew PSU Problems

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Originally Posted by Electronpusher0 View Post
, check the voltage between the adjust pin and output, this should be 1.25V, i
Peter
Yup surprisingly enough they seem to be genuine, As tha'ts the voltage I'm getting between adjust and the output
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Old 7th Oct 2022, 7:42 am   #28
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Default Re: Homebrew PSU Problems

Interestinger and interestinger,
At this stage I would try the following
Try an LM317 from a different source.
Try the regulator circuit on a bench power supply, not the battery charger, to narrow down the problem.
And try as Sideband says in post 13 to mount the capacitors as close to the regulator as possible.

Peter
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Old 7th Oct 2022, 11:01 am   #29
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Default Re: Homebrew PSU Problems

Quote:
Originally Posted by Electronpusher0 View Post
Interestinger and interestinger,
At this stage I would try the following
Try an LM317 from a different source.
Try the regulator circuit on a bench power supply, not the battery charger, to narrow down the problem.
And try as Sideband says in post 13 to mount the capacitors as close to the regulator as possible.

Peter
It's working as intended now peter, I Can only put it down to a faulty potentiometer, But why changing the regulator temporarily fixed the problem i haven't a clue.

Jay
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Old 8th Oct 2022, 10:20 pm   #30
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Default Re: Homebrew PSU Problems

Are you using your homebrew PSU to charge batteries?
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Old 8th Oct 2022, 10:23 pm   #31
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Default Re: Homebrew PSU Problems

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Originally Posted by Silicon View Post
Are you using your homebrew PSU to charge batteries?
No. It's just a general power supply for projects etc.
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