power supply question

odysseybmx414 · 23rd February 2005, 09:58 PM

i have a 200va transformer with 20v secondaries i was wanted to know about how many dc volts would this produce? the transformer is rated at 3 amps. And, would this be able to supply a single lm4780 amp?

vmac011 · 24th February 2005, 01:01 AM

AC x SQR(2)

in your case 20 Vac x 1.41 = 28.2 Vdc

That transformer is fine for 1 4780 chip.

filholder · 24th February 2005, 01:36 AM

Should produce 28 volts dc. And i would think from what i have read that would be enough for one chip amp.

K-amps · 24th February 2005, 01:39 AM

Quote:

Originally posted by filholder
Should produce 28 volts dc. And i would think from what i have read that would be enough for one chip amp.

Actual DC will be 26.7 to 27.2 depending on the forward voltage drop of the rectifiers you use. They need 1-1.5 volts to forward bias.

Leolabs · 24th February 2005, 02:00 AM

It also depends on the value of the filtering cap.

I recently build an amp with experience like this:

Transformer secondary voltage:34V-0V-34V(approax)

Rectification:full wave bridge

DCV with 4700uF:41V(approax)

DCV with 4700uF+470uF:46V(approax)

odysseybmx414 · 24th February 2005, 08:02 AM

big help guys thanx

K-amps · 24th February 2005, 10:50 AM

Quote:

Originally posted by Leolabs
It also depends on the value of the filtering cap.

I recently build an amp with experience like this:

Transformer secondary voltage:34V-0V-34V(approax)

Rectification:full wave bridge

DCV with 4700uF:41V(approax)

DCV with 4700uF+470uF:46V(approax)

Leo... a 12% increase by using a bypass cap

seems like a lot....

jacco vermeulen · 24th February 2005, 10:57 AM

Quote:

Originally posted by Leolabs
It also depends on the value of the filtering cap.
DCV with 4700uF:41V(approax)
DCV with 4700uF+470uF:46V(approax)

Can i have some of those caps ?

Leolabs · 24th February 2005, 11:06 AM

Strange hah???That's what came out,more capacitance more voltage.No idea what cause this.

K-amps · 24th February 2005, 11:21 AM

Quote:

Originally posted by Leolabs
Strange hah???That's what came out,more capacitance more voltage.No idea what cause this.

Not just strange... this is bordering funky. Is the experiment repeatable , with different values? I mean I never got a 10-12% increase by doubling my caps let alone slightly increasing them. Granted for very low levels of capacitance, you will get some gain of rails especially under load, but this is too good..... to be real.

23rd February 2005, 09:58 PM	#1
odysseybmx414 diyAudio Member Join Date: Feb 2005 Location: Watertown, NY	power supply question i have a 200va transformer with 20v secondaries i was wanted to know about how many dc volts would this produce? the transformer is rated at 3 amps. And, would this be able to supply a single lm4780 amp?

24th February 2005, 01:01 AM	#2
vmac011 diyAudio Member Join Date: Aug 2004 Location: Serbia	AC x SQR(2) in your case 20 Vac x 1.41 = 28.2 Vdc That transformer is fine for 1 4780 chip. __________________ Tesla boyz

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24th February 2005, 01:36 AM	#3
filholder diyAudio Member Join Date: Jan 2005 Location: london	Should produce 28 volts dc. And i would think from what i have read that would be enough for one chip amp.

24th February 2005, 02:00 AM	#5
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	It also depends on the value of the filtering cap. I recently build an amp with experience like this: Transformer secondary voltage:34V-0V-34V(approax) Rectification:full wave bridge DCV with 4700uF:41V(approax) DCV with 4700uF+470uF:46V(approax)

24th February 2005, 08:02 AM	#6
odysseybmx414 diyAudio Member Join Date: Feb 2005 Location: Watertown, NY	big help guys thanx

24th February 2005, 11:06 AM	#9
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Strange hah???That's what came out,more capacitance more voltage.No idea what cause this.

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