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Old 30th May 2012, 09:56 PM   #1
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Default 24VDC to ~15VDC without a regulator

Hi!

I have a simple audio preamplifier that uses two TL072 op amps, but my supply is ±24V and the TL072's has a max supply voltage of ±18V. The proper way to do this would be using regulators, but I have none available and getting them can take days where I live. A second possibility is using only the +24V rail and operating the opamps with biased inputs, but this involves a lot a coupling capacitors so I'd rather avoid it.

My question is this: is it safe/sane to use a simple voltage divider on both rails (eg. two 1.5k 1W resistors) to get the voltage down to say ±12V (which is ample for my circuit)? The op amps will drive only high impedance sources (>10k) so I would not expect the output current to load the voltage divider so much that the supply voltage drops noticeable, but I'm not 100% sure. What other considerations do I need to make?

Any thoughts are appreciated and my apologies if this already has been answered on the forums!
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Old 31st May 2012, 12:34 AM   #2
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It could work. You'll probably want to try to use the lowest value resistors in the voltage dividers that you can,this will help get the supply impedance down a bit,and the voltages possibly more stable,at the expense of extra power (heat) in the resistors,and extra load on the power transformer.
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Old 31st May 2012, 01:37 AM   #3
wwenze is offline wwenze  Singapore
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Add electrolytic caps between the +12V and ground (same for -12V) to reduce the power supply impedance for AC frequencies.
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Old 31st May 2012, 06:17 AM   #4
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Excellent, thanks a lot guys! I will give it a try.
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Old 31st May 2012, 06:55 AM   #5
Elvee is offline Elvee  Belgium
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Don't you have zeners available? That would be preferable to a resistive divider.
If you don't have any zeners, you could substitute Vbe multipliers. Or, if you have zeners of the wrong voltage, an hybrid Vbe+zener multiplier.
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