Circuit Sanity Check: +15V, -15V, +9V Power Supply - diyAudio
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Old 18th July 2009, 03:44 PM   #1
miallen is offline miallen  United States
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Default Circuit Sanity Check: +15V, -15V, +9V Power Supply

Hi,

Can someone sanity check my power supply circuit?

http://207.192.69.113/~miallen/MixerSupply2.pdf

I'm not an engineer and to this point I have been pretty much implemented existing schematics from books and the Internet. This time I'm trying to squeeze this onto one of those 1-3/4" square perfboards so I improvised with the parts a little.

I have bread board tested the +15 supply and I will do the same for the +9 sub-circuit so that know exact resistor values.

Actually one thing I'm not really sure about is that some of these sort of supplies use 1/2 W resistors. I wasn't sure if it was necessary in this case.

The +15V, 0, -15V at 0.239 A torriodal transformer for this project is only 7 VA. Devices connected to this supply could draw 100mA but I would hope that it could handle more.

The voltage regulators will all be mounted to a 3/8" thick slab of aluminum that divides the power supply from the rest of the enclosure.

Mike
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Old 18th July 2009, 04:14 PM   #2
infinia is offline infinia  United States
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Hi
Everything looks OK so far.
Where is the rectifier mounted? Did you calculate the V adj range?
The calculated resistors wattage s/b at least lesss than 1/2 the rated. You can do that from the data sheets by either subtracting or adding I adj. and using max V adjust.
You could post your transformer data sheet for us.
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Old 18th July 2009, 05:25 PM   #3
mjf is offline mjf  Austria
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hello.
please have a look at the pin connection of the lm 337(datasheet)........pin2 = input, pin3 = output i think.
greetings..........
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Old 18th July 2009, 07:06 PM   #4
miallen is offline miallen  United States
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I bread board tested the trimmer range for +15V if that is what you mean. I don't recall what the range was but it can go well above 15V. If I have it set to 15.0V and quickly move a pot across the load, I cannot see any twitch in voltage with my DMM.

I'm about to bread board test the +9V sub-circuit to figure out what resistor values will be used exactly.

I'm not sure how to compute the wattage for the resistors. I have seen some schematics with 2A transformers and supposedly 37V output with and without 1/2 W resistors so I assume that if I'm using a 233mA transformer at 15V, I should be ok.

But I'm not sure because it seems 15V * 0.2A is 3W. But of course that power is distributed over two resistors in series. I compute voltage drops of 1.4V and 13.6V so 13.6^2/2700 is 69mW?

What are the power ratings of those little trimmers when in a low-resistance position? I just got a "grab bag" of trimmers so I don't have databsheets for them.

Anyway, here is the datasheet for the transformer (I have the one with the 15V secondary):

http://www.farnell.com/datasheets/320644.pdf

The only other thing I'm concerned about is if the capacitors are big enough to handle the load and to sufficiently minimize ripple. Again, I'm dealing with very tight space constraints but notice I did make C4 quite a bit larger than it's -15V counterpart since it's also supplying the +9V sub-circuit.

And to mjf, yes, I forgot to mention the LM317 pins are positioned incorrectly in the schematic. The schematic software I used (gschem) apparently does not have a symbol for LM317. So I just relabelled an LM337 symbol but could not figure out how to renumber the pins.

Mike
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Old 18th July 2009, 07:18 PM   #5
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No Cadj capacitor for the 9V supply.
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