Bridge rectifier power source

imsellingmyfoot · 21st December 2010, 02:44 AM

I am having problems with a bridge rectifier power source I built. I have traced the problem to the rectifier diode I am using. My voltage going into the diode is ~25 VAC. My voltage coming out as DC should be the same, one positive and one negative, correct? My multimeter is reading negative ~29 V DC and positive ~6 V DC. The diode was spec'ed as 8 amp and 400V tolerances. Is there a possibility that there is something wrong with my circuit (I don't think so), or is this just a diode that is messed up?

Thanks

bob91343 · 21st December 2010, 06:31 AM

I think the problem is in your measurement. You measure 29 and 6 Volts with respect to what? A bridge rectifier has only two output wires and you measure between them.

aardvarkash10 · 21st December 2010, 07:06 AM

(25 x 1.414) - rectifier losses = 35-ish (or, 29 + 6)

Well done Sherlock!

imsellingmyfoot · 21st December 2010, 07:19 AM

Measuring across from the positive lead to the negative lead gives me ~37 V.

My drawing says coming out of the diode should be +22V and -22V but I am using a different transformer, therefore my numbers are higher. Shouldn't my positive and negatives be equal though?

DF96 · 21st December 2010, 02:37 PM

Is the centre-tap of the transformer grounded? Does it have a centre-tap? If not, you are in effect measuring via the leakage resistance of the transformer (or something).

21st December 2010, 02:44 AM	#1
imsellingmyfoot diyAudio Member Join Date: Dec 2010	Bridge rectifier power source I am having problems with a bridge rectifier power source I built. I have traced the problem to the rectifier diode I am using. My voltage going into the diode is ~25 VAC. My voltage coming out as DC should be the same, one positive and one negative, correct? My multimeter is reading negative ~29 V DC and positive ~6 V DC. The diode was spec'ed as 8 amp and 400V tolerances. Is there a possibility that there is something wrong with my circuit (I don't think so), or is this just a diode that is messed up? Thanks

21st December 2010, 07:06 AM	#3
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	(25 x 1.414) - rectifier losses = 35-ish (or, 29 + 6) Well done Sherlock! __________________ Yes, conservatism thrives on low intelligence and poor information. But the liberals in politics... continue to back off, yielding to the supremacy of the stupid. It's turkeys all the way down. - George Monbiot, guardian.co.uk, 6 Feb 2012

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21st December 2010, 06:31 AM	#2
bob91343 diyAudio Member Join Date: Mar 2010	I think the problem is in your measurement. You measure 29 and 6 Volts with respect to what? A bridge rectifier has only two output wires and you measure between them.

21st December 2010, 07:19 AM	#4
imsellingmyfoot diyAudio Member Join Date: Dec 2010	Measuring across from the positive lead to the negative lead gives me ~37 V. My drawing says coming out of the diode should be +22V and -22V but I am using a different transformer, therefore my numbers are higher. Shouldn't my positive and negatives be equal though?

21st December 2010, 02:37 PM	#5
DF96 diyAudio Member Join Date: May 2007	Is the centre-tap of the transformer grounded? Does it have a centre-tap? If not, you are in effect measuring via the leakage resistance of the transformer (or something).

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