Current amplifier with bipolar transistor

[glias]

Hi all,
I would want to amplify a DC current from a generator provided by an op amp... I would want to use a bipolar transistor but I'm not familiar in biasing in "DC current amplification mode". The output current should be equal to 100mA.

What kind of topology can I use ? and what kind of biaising should I use ?

regards

 

[albbg]

A bjt transistor is essentially a current amplifier. You could use a simple common collector connection, that means: collector directly connected to Vcc, Base connected to current generator (better if through a resistor in order to avoid large base current to flow in case of failures) and emitter connected to the load (other end of the load connected to ground). The current gain is roughly equal to the beta of the transistor you choose.
The supply voltage has to be choosen taking into account that saturation will arise when impedance of the load multiplied by maximum output current exceed the supply voltage.
A so simple circuit has many problems:

1) Gain is not controllable since it depends only from the bjt (so it can vary part to part)
2) Gain depends from the temperature
3) linearity of the transfert function Iout/Iin is not very good

However, depending from your application, it could be OK.

 

[IanP]

You can consider simple emitter follower or so called complementary emitter follower .. see attached picture ..
Both configurations will easily boost the output current and depending on the Hfe of transistors 100mA shouldn’t be difficult to achieve ..

Alsos see:
**broken link removed**

Rgds,
IanP

 

[FvM]

With higher signal frequencies and/or quality requirements, a class B output stage may be unsuitable due to it's cross-over
distortions. A BE-parallel resistor can slightly improve the linearity at low signal voltages. If you don't want polarity reversal,
you can use a non-inverting OP configuration with the buffer.