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Author Topic: Negative voltage regulators  (Read 295 times)
K0IPG
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Posts: 252




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« on: October 26, 2002, 07:57:09 PM »

Hello all,
   I have about four dozen negative voltage regulators (7906's and 7912's, I believe) that I found in the junk box. I really don't have a need to regulate negative voltages, but postive ones would be nice! Is there any way I could use these for postive voltage regulation, without a prohibitive amount of extra circuitry?
   I understand the best thing would be to have postive voltage regulators, but I just hate to see a good part go to waste Smiley.

Thanks,
Dan
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AC5UP
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Posts: 3864




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« Reply #1 on: October 26, 2002, 11:11:29 PM »

The only difference between a positive and negative regulator involves which side of the circuit is held at a constant reference level... A negative regulator works 'upside down' by adding a variable series resistance to the negative leg of the circuit.

This is not a problem for a simple circuit that doesn't care about an absolute ground reference, like pilot lights or an LED display. For something like a low-level preamp that doesn't draw much current you can bypass the negative leg with a series capacitor so the AC signal component will continue to see a common ground. You can also add an 'NPN wrap-around' pass transistor to increase the current capacity.

With that said, I wouldn't trust a work-around that doesn't have a true DC ground reference, no matter how clever, as a power supply for anything of value. Considering how cheap TO-220 regulators can be found, better you should keep the negative regulators in the junk box against the day you decide to tinker with op amps that need a split power supply.

- AC5UP
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