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Old 18th April 2006, 06:58 AM   #1
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Default PSU check

I'm woundering if this is good enough for a 200W amp I'm making.
It will be running maybe 8-10 op-amps so I assumed 50mA is good enough?

Any improvments I could do?

I used a half bridge design for the op-amp power supply because the L78/9XX series can only handle 35V max input.
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Old 18th April 2006, 08:13 AM   #2
Eva is offline Eva  Spain
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Either with half bridge or with full bridge, you are going to get also +-56V on the op-amp supply. You have to look for another approach to drop the voltage, this one will fail in quite an ugly way.
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Old 18th April 2006, 10:04 AM   #3
lndm is offline lndm  Australia
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I would have to agree with Eva.

Fortunately, 20VA 12+12 or 15+15 toroids are dirt cheap.
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Old 19th April 2006, 04:46 AM   #4
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Duhhhhh!!!!!!! stupid me I see now, I'll only get +/- 56V with a hell of a lot more ripple with that design.

Another transformer is not an option for me due to the space limitations, but do you know of any other design type I could go with or am I stuck going with the good old discrete.

I was thinking of putting a resistor in series with the regulators input but there mite be times where these no load on the regs hence the voltage would go back up to B+.

I think a divider network would be too inefficent than I want, so I would like it if anyone had any good ideas.

Thanks David.
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Old 19th April 2006, 04:54 AM   #5
Eva is offline Eva  Spain
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You can always protect the regulators with a 30V or 35V zener.
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Old 19th April 2006, 09:01 AM   #6
Pierre is offline Pierre  France
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If your +/-15V circuit consumption is know or constant, you can put 2W resistors in series with the input of the 7X15 regulators, so the resistors drop around 25V. This is practical for current draws up to 60-70mA.

Try to balance the power dissipation between the resistor and regulator. 1W each would be good.

This approach has an advantage: you can use a electrolytic cap in between the regulator input and GND so you will have a RC lowpass filter that can reduce noise to the regulator. It is also cheaper than using zeners, but it is optimal for a very limited range of current consumptions.

Just an idea.
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Old 19th April 2006, 11:08 AM   #7
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Consider the following pre-regulator solution before the 78xx: http://sound.westhost.com/project102.htm
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Old 21st April 2006, 04:56 AM   #8
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Well I decided to go with discrete regulator, it seems to be a bit more protection. 50mA was a guess at worst case current consumtion so it wouldn't be even close to that while running. This one on paper should be able to do around 100mA of current to the load anytime.

If you see anything wrong or that could be improved please tell me

Thanks

David
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