Electronics > Beginners
Voltage Regulator
staticshock:
I have op-amps in my circuit that need +/- 16.5V or roughly (16V-18V). However, the DC Voltage available is 28V and will need to step it down. Using LP2951 and simulating in PSpice I can get +16.5V, but either I'm clueless or if my brain is fried at the moment I'm not sure of how to get -16.5V. Any help?
bob91343:
You didn't say the current drain. There are IC regulators both pos and neg for a wide variety of voltages. If you need more current you can add a power transistor.
lordvader88:
If the supply voltage of the op-amp is bigger than u need, then it will still work fine, as long it's it not over the rated limit. But if the same supply is used in biasing/etc, then some values of parts would be changed.
LM317 and LM337 chips are very common and cheap adjustable +/- regulators, like LM7812 and LM7912 +12/-12 regulators.
mariush:
There are voltage doubler/inverter ICs which can take some voltage and output the negative.
For example
40mA max : TC7662ACPA https://www.digikey.com/product-detail/en/microchip-technology/TC7662ACPA/TC7662ACPA-ND/115287
80mA max : TC962CPA https://www.digikey.com/product-detail/en/microchip-technology/TC962CPA/TC962CPA-ND/115289
So you could have any ldo to produce 16.5v and then use one of the chips above to produce -16.5v
If you want something cheaper, you could go with one of the 34063 or 33063 switching regulators and configure them in inverting mode.
There's calculator on Sourceforce https://sourceforge.net/projects/mc34063uc/ and there's online calculators as well : http://www.nomad.ee/micros/mc34063a/
SparkyFX:
Voltage doubler circuits: https://en.wikipedia.org/wiki/Voltage_doubler
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