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Old 25th May 2013, 03:55 PM   #1
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Default which transformer to use for this regulated supply?

Hi guys,

while stumbling over the internet looking for +-15v good regulated supply using 317/337 i stumbled upon this link which i chose for the construction of my supply as this is the easiest no frills +-15v schematic i can ever get

http://audio.gotroot.ca/minipow/

i havent been able to find the transformer rating. can someone help me with that? will 12-0-12@ >25VA work fine with this?

does someone have a BETTER and simpler circuit for a clean +-15v than this?

Last edited by godslayer; 25th May 2013 at 03:57 PM. Reason: link provided
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Old 25th May 2013, 04:12 PM   #2
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I don't see the point of so much filter capacitance before the regulator. Otherwise, it seems pretty standard as shown in the 317 application note.

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Old 25th May 2013, 04:31 PM   #3
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... just noticed that I did not really answer your question.

12VAC will give approx. 18VDC rectified, minus the voltage drop of two diodes (1.4V). This does not leave enough headroom for the regulator, especially with some mains variations, IMHO.

LM337 is capable of 1.5A, I seem to remember, better check it in the datasheet. So the maximum sensible current draw is 1.5A per rail, meaning 30V*1.5A = 45W. I would use at least 50-70VA transformer, unless you definitely know you will not be drawing that much current.

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Old 25th May 2013, 04:41 PM   #4
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i wont be drawing much current, i just need the supply for p88 (esp) and one bass filter cutoff ie all in all driving 4 opamps... ill go for higher one, maybe 15-0-15 @ 2a(60va) thanks for the help

as for the complications you mentioned, will this circuit work? given that i use only 15v network? is it suitable enough for Audio application(i see varied register networks than previous circuit)?

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Old 25th May 2013, 06:04 PM   #5
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15+15Vac is perfect for a regulated 15+15Vdc
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Old 25th May 2013, 06:31 PM   #6
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Quote:
Originally Posted by AndrewT View Post
15+15Vac is perfect for a regulated 15+15Vdc
can i also have your critique on the above circuit?
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Old 26th May 2013, 07:37 AM   #7
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LED5 is being run very hard
R38 might be a bit high.
The switching is going to send ~23V pulses to the outputs.
C1, 2, 9 & 10 are shown in the wrong locations.
The continuous Zero Volts wire from chassis to GND is wrong.
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Old 26th May 2013, 09:29 AM   #8
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Quote:
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15+15Vac is perfect for a regulated 15+15Vdc
yes, but down to 3 volts out your regulator is wasting most of the power...
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Old 26th May 2013, 05:48 PM   #9
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yes, but down to 3 volts out your regulator is wasting most of the power...
i have a spare 13-0-13v @ 75va one lying in my drawer. i guess that will be perfect.

26v-> 36vdc minus the diode drop
2a-> 1.27A dc

36v dc 3v for each regulator to regulate. i guess things are better like this.

i will go with minipow supply then.
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Old 26th May 2013, 07:14 PM   #10
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Quote:
Originally Posted by AndrewT View Post
LED5 is being run very hard
R38 might be a bit high.
Typo?
Looks like the LED receives ~15mA; R38 could probably be increased in value.
Quote:
Originally Posted by Tony View Post
yes, but down to 3 volts out your regulator is wasting most of the power...
Maybe not "most of the power," but more than necessary.
For a handful of op amps, either the 26VCT or 30VCT transformers should be more than big enough.
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