Smallest way to get -5v

**phil.45** · 07-24-2002, 05:10 AM

What is the smallest (least number of support components) method I can use to get -5v? My PSU was finished a long time ago and has zero space inside, but I now need to use my serial port so I have to add -5v. Is there such a thing as a linear reg that can do this?

**Rob** · 07-26-2002, 05:10 PM

All linear regulators will require a negative supply to generate a negative voltage. If you've already got a -12v supply then you can simply use a LM7905 voltage regulator along with a couple of caps on the input and output. If you don't have a negative supply to start with then your best bet is a MAX774 switch mode chip click here for details.

**eugenen** · 07-26-2002, 06:17 PM

Unless you have a strange MB, you need -12 for serial ports. -5 is hardly ever used for anything anymore.

**phil.45** · 07-27-2002, 04:04 AM

Yeah, its for serial port, and I dont have a -12v line cause I never needed before.

Guess Ill have to bite the bullet and order prts to built the Maxim 774/775/776 supply.

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