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Old 23rd February 2005, 08:58 PM   #1
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Default 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?
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Old 24th February 2005, 12:01 AM   #2
vmac011 is offline vmac011  Serbia
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AC x SQR(2)

in your case 20 Vac x 1.41 = 28.2 Vdc

That transformer is fine for 1 4780 chip.
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Old 24th February 2005, 12:36 AM   #3
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Should produce 28 volts dc. And i would think from what i have read that would be enough for one chip amp.
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Old 24th February 2005, 12:39 AM   #4
K-amps is offline K-amps  United States
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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.
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Old 24th February 2005, 01:00 AM   #5
Leolabs is offline Leolabs  Malaysia
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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)
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Old 24th February 2005, 07:02 AM   #6
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big help guys thanx
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Old 24th February 2005, 09:50 AM   #7
K-amps is offline K-amps  United States
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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....
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Old 24th February 2005, 09:57 AM   #8
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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 ?
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Old 24th February 2005, 10:06 AM   #9
Leolabs is offline Leolabs  Malaysia
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Strange hah???That's what came out,more capacitance more voltage.No idea what cause this.
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Old 24th February 2005, 10:21 AM   #10
K-amps is offline K-amps  United States
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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.
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