power supply problem...

Thread Starter

WAN24

Joined Jun 27, 2006
21
gud day sir!!

im working on a power supply with 3 different regulators to power my project(op-amp circuits).. +5v, +12 and -12v... the input for the rectifier is 12v 750mA AC.. (the schematic is attached) the problem is that im only getting 5v on the outputs... i've checked the circuit board, changed the regulators... and still, the same problem :confused: .. any suggestions or corrections on my circuits...

tnx in advance!!!
 

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thingmaker3

Joined May 16, 2005
5,084
The 7912 cannot change the polarity of supplied voltage. You need to provide negative voltage in to get negative regulated voltage out.

Continue to use transground as ground, but do not connect the rectifier to ground - instead connect rectifier negative to the 7912.

I have no idea why the 7812 would put out 5V. Are you certain of your components?
 

Thread Starter

WAN24

Joined Jun 27, 2006
21
tnx sir for the immediate reply... i only designed this circuit... im going to changed the input for 7912... any more suggestions or corrections on my circuit sir? again.. thank you so much sir!!
 

beenthere

Joined Apr 20, 2004
15,819
On the schematic, the AC is applied to the DC output terminals of the bridge rectifier. You need to look at the schematic (and the circuit) and make sure the AC goes to the right places on the bridge.
 

Thread Starter

WAN24

Joined Jun 27, 2006
21
ooopppsss.. my wrong... but, i already checked it and change the terminals... and still problems above persist.. but maybe the 7912 is solved.. only the 5v output for the 7812 is the problem...
 

beenthere

Joined Apr 20, 2004
15,819
You need to update the schematic and repost it. The filter capacitor on the bridge is incorrect, the DC voltage comes from one line, meaning there is no negative voltage, and so on. We can't tell what might still be wrong until the schematic is corrected.
 

nomurphy

Joined Aug 8, 2005
567
Check you connections per the attached.

Also, the transformer needs to be ~24VAC secondary, or a dual 12VAC secondary connected in series. A 12VAC secondary that is center-tapped will only provide 6VAC to each side of (+) and (-), which will be about 9VDC or less, and this is probably why the 12V output is low.
 

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Audioguru

Joined Dec 20, 2007
11,251
Where are my posts?
Oh, they are on another website.

I think the regulators are destroyed from having the bridge rectifier connected wrong.
 

Thread Starter

WAN24

Joined Jun 27, 2006
21
ok sir.. thanks for the help... im going to change my circuit and tell you what happen... again, w/ due respect.. thank you guys..
 
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