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how to generate negative voltage?

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trashbox

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Hi all,

#1.
I need to add a negative voltage on the PCB for my test chip, the average output current is about 100mA through this voltage. Except the charge pump chip, how can I realize a negative voltage with simple method on PCB?

#2.
I also need a big size mosfet (power transistor?) with source follower connection for my test chip's power supply. It means this nmos source is connected with my test chip's power, drain is connected with PCB power. How can I find such a mosfet?

Thanks in advance!
 

kender

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#1. There are buck-boost converters (a type of SMPS topology). They produce negative voltage with respect to input. If you have AC on the board, you can make the negative supply rail using a rectifier (half way probably, another half for positive rail) and a linear negative regulator (e.g. LM7905). For 100mA, I would use a charge pump, though. Is there a reason not to use it?
 

FvM

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#2. I use to find them in the manufacturer's selection guides.
 

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