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Help with Voltage Regulator Answered

Hi,

I have put one of these together for an ATX power supply and have come across something that I might be getting wrong....

In mocking up the LM317 circuit in breadboard (standar one found everywhere on line and on the LM317 pages), I have got the thing metering -11v to +11v??? I am using one of the black ground wires of the PSU on the black side of the volt meter, but cant figure out why I am not just getting positive voltages??? Could the diode be faulty? Or is this in fact correct?

Any help appreciated...

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lone_viper
lone_viper

8 years ago

Hi,

I have another quick question...

In the standard LM317 circuit, are both Caps needed? And if so what other values could be used as I am trying to use up some spare kit and dont have a 0.1 or 1uF to hand....

I know I could go out and buy them but I like to recycle..... I have something that seems to work for the inbound, which is close to 0.1uF, but not for the output, and it still seems to work ok?

Any help appreciated.

Kind regards

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steveastrouk
steveastrouk

Reply 8 years ago

Not mandatory, put the 0.1 on the output.

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lone_viper
lone_viper

9 years ago

Hi all,

Thanks for the support.

In response;

Meter is set to DC 20 and as I turn the POT the voltage goes from -11 to +11.
I am using one of the PSU black ground wires as the metered negative not the -12v rail.

Kind regards

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steveastrouk
steveastrouk

Reply 9 years ago

As I said in your question, the ground for your 317 is probably not the one you're measuring the output from.

Steve

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lone_viper
lone_viper

Reply 9 years ago

Ok so am I right in thinking that I have to use the -12v rail effectively for the grounding post for this to work??

That might be where I am going wrong as I was using one of the black grounds?

I have tried again and putting the meter COM on the -12 and then dialling up the POT I get 1.3v to 22v

Could I ask for confirmation :-)

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steveastrouk
steveastrouk

Reply 9 years ago

YES.

And you have proved my point !

Please go back to the question and mark the Best Answer.

Steve

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mpilchfamily
mpilchfamily

9 years ago

Is the meter displaying -11V then jumping up to 11V? What do you have your meter set at?