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Designing of 1mA constanta current source

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rocker1025

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Dear Sir,

For designing of 1mA,10mA or any current source MOSFET is used why not BJT, can anyone explain me?
And also tell me how to design 1mA and 10mA constant current source using PMOSFET?
 

BJT is an active device. it is a current controlled valve. The base current controls the collector current. can be good for its low capacitance switch. complex circuitry, noise amps and less cost.
MOSFET is an active device. it is a voltage controlled valve. VGS controls the drain current. when it is designed as current source, it is having very less noise. as a voltage controlled device it is easy to limit the current as per the user requirement. simply it is "Single Chip Curent Source"
you can find enormous basic circuitry in this forum itself. else google it.
Hope it helps
 

Thank you sir,
Can you tell me how to design constant current source?

embedsys said:
BJT is an active device. it is a current controlled valve. The base current controls the collector current. can be good for its low capacitance switch. complex circuitry, noise amps and less cost.
MOSFET is an active device. it is a voltage controlled valve. VGS controls the drain current. when it is designed as current source, it is having very less noise. as a voltage controlled device it is easy to limit the current as per the user requirement. simply it is "Single Chip Curent Source"
you can find enormous basic circuitry in this forum itself. else google it.
Hope it helps
Click to expand...
 

I guess, the original poster is looking for an OP current source like this:



It can be made with a PNP transistor as well, but the base current creates an error term. A BJT darlington usually reduces this error below the achievable circuit accuracy limits.
 
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