In my project, I need to make current amplifier which have < 2mA input current and > 100 mA output current.
Actually, I want to fully understand the BJT circuit, and then making a proper amplifier circuit.
But project deadline is soon, so I just want to make the amplifier first.

present circuit with two TIP122 (NPN BJT) is follow,

My goal is applying the linearly amplified AC current (100~200 mA) in R_load.

The problem is ...
- Signal source have current limitation ( maximum current : 2 mA, maximum voltage : -10 ~ +10 V ).
- R3 have big DC current so, It is easily heated.
- non-linearly amplified...

So, can you suggest proper amplifier circuit for this situation?
If you give some circuit scheme with detail parameter ( Ohm, Volts, Capacitance, etc. ), would be perfect!

Thank you!

// summary
with 2 TIP 122,
- Input AC signal : -10 V ~ +10 V sine wave (current limit ~ 2mA).
- output AC signal : linearly amplified sine wave ( 100~ 200 mA )

 

hi HiThanks.
Is this a college assignment, if yes, I will move it to the Homework Forum, should improve responses.
E

 

hi,
If you are trying to test a Current amp, you should use a current input source.
I will post a LTSpice sim of your circuit.
E

EDIT:
This is what I see with your circuit.

 

You need to AC couple the input signal with a series capacitor if want to amplify AC.

What is the purpose of R3 if you have a 5 ohm resistive load?
Do you want the load to see only AC?
If so, you need to AC couple the load also.

 

You need to AC couple the input signal with a series capacitor if want to amplify AC.

What is the purpose of R3 if you have a 5 ohm resistive load?
Do you want the load to see only AC?
If so, you need to AC couple the load also.

with output cap, what happens to negative swing as cap discharges through R3 compared to charging through Rload

 

with output cap, what happens to negative swing as cap discharges through R3 compared to charging through Rload

It limits the magnitude of the negative swing. as compared to the positive swing.

 

Thank you guys. I figured out.