Why do I only get 8.9v from a 12v voltage regulator?

Haz · 24th January 2011, 04:34 PM

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!!

Zeta4 · 24th January 2011, 04:41 PM

Hi

Isnt an LV7912 a negative voltage reg? You mention 12V positive.

Haz · 24th January 2011, 04:44 PM

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?

StevenOH · 24th January 2011, 04:46 PM

Maybe, because you expect positive 12V from a negative regulator:-)

Haz · 24th January 2011, 04:48 PM

I do not know there was 2 types it was a simple mistake I thought they were all the same

AndrewT · 24th January 2011, 04:53 PM

the pin out of a 79xx is different from a 78xx. So too is the 317 different from the 337 pin out.

Haz · 24th January 2011, 04:58 PM

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!!

luka · 25th January 2011, 05:28 AM

you and me both LOL

24th January 2011, 04:34 PM	#1
Haz diyAudio Member Join Date: Oct 2010	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!!

24th January 2011, 04:46 PM	#4
StevenOH diyAudio Member Join Date: Jun 2004 Location: USA	Maybe, because you expect positive 12V from a negative regulator:-) __________________ The truth is out there. Who can handle the truth?

24th January 2011, 04:53 PM	#6
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	the pin out of a 79xx is different from a 78xx. So too is the 317 different from the 337 pin out. __________________ regards Andrew T.

25th January 2011, 05:28 AM	#8
luka diyAudio Member Join Date: Sep 2005 Location: in Slovenia :)	you and me both LOL __________________ home page @ http://www.classdaudio.co.cc @ 24/7 all year long I FEEL SLOVENIA

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24th January 2011, 04:41 PM	#2
Zeta4 diyAudio Member Join Date: Aug 2005	Hi Isnt an LV7912 a negative voltage reg? You mention 12V positive.

24th January 2011, 04:44 PM	#3
Haz diyAudio Member Join Date: Oct 2010	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?

24th January 2011, 04:48 PM	#5
Haz diyAudio Member Join Date: Oct 2010	I do not know there was 2 types it was a simple mistake I thought they were all the same

24th January 2011, 04:58 PM	#7
Haz diyAudio Member Join Date: Oct 2010	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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