Why do I only get 8.9v from a 12v voltage regulator? - diyAudio
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Old 24th January 2011, 04:34 PM   #1
Haz is offline Haz  United Kingdom
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Angry Why do I only get 8.9v from a 12v voltage regulator?

OK So I want to step down 27v from a meanwell switching power-supply to 12v to power a tube buffer stage as part of my amplifier project.

But when I wire everything correctly with the first pin on the L7912CV getting the 27v DC and both GND's to the middle pin and the 12v positive to the last pin I only get 8.9v.

At first I thought it could be a faulty voltage regulator but I've tried 2 and there both doing this.

It worked perfect when I tried a 5v voltage regulator so what going on here? the power I'm using it well with in the limit of the L7912CV.

My only conclusion is they are both faulty. But can any more experienced person tell me what's going on here?

Many thanks for any help!!
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Old 24th January 2011, 04:41 PM   #2
Zeta4 is offline Zeta4  United Kingdom
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Hi

Isnt an LV7912 a negative voltage reg? You mention 12V positive.
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Old 24th January 2011, 04:44 PM   #3
Haz is offline Haz  United Kingdom
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Yeah I just found out it is, So I've got the wrong type.

Voltage Regulator L7812CV L7812 +12V 7812 (Pack of 2) on eBay (end time 05-Feb-11 21:04:51 GMT)

Are these the correct ones?
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Old 24th January 2011, 04:46 PM   #4
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Maybe, because you expect positive 12V from a negative regulator:-)
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Old 24th January 2011, 04:48 PM   #5
Haz is offline Haz  United Kingdom
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I do not know there was 2 types it was a simple mistake I thought they were all the same
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Old 24th January 2011, 04:53 PM   #6
AndrewT is offline AndrewT  Scotland
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the pin out of a 79xx is different from a 78xx. So too is the 317 different from the 337 pin out.
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Old 24th January 2011, 04:58 PM   #7
Haz is offline Haz  United Kingdom
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Yeah the first pin its the GND the middle pin is the input and the last is the output. I'm surprised it worked at all!!
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Old 25th January 2011, 05:28 AM   #8
luka is offline luka  Slovenia
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