I have a 2N2222A transistor that I use in a circuit coupled with an opamp. Its function is to act as a current booster.
The collector is always supplied with 12V and the emitter can be set anywhere between 0 – 8 V. I was not aware about overheating my transistor, and I believe I've burnt my transistor when I have a current of about 200mA passing through it, when the VC was 12V and VE about 6V.
I want to replace it with one that can handle the power yet not hinder performance. I am also willing to buy heat sinks for the packages.
The range of current I am expecting for this transistor to drive is anywhere between 0 and 300 mA.
I was thinking of this transistor with this heat sink.
Best Answer
Specs:
Input: 12V 0~0.3A
Ouput: 0 to 8V 0~0.3A
Max Case temp rise: 40'C
Speed: not important
Heatsink: 24'C/W convection +X with thermal grease, insulator
Design:
Linear Loss 4V*0.3A = 1.2W
Est: 30'C/W * 1.2W= 36'C rise. OK
WIth 4V > Vce < 12V , the best choice for high hFE is a Darlington TO-220 with this heatsink.
MJD122-1 $0.90 (1) https://www.digikey.com/product-detail/en/stmicroelectronics/MJD122-1/497-16183-ND/3087726
For better linear operation with step load low overshoot, use BJT Op AMP not CMOS R2R type. Even a lowly uA741 would work or LM324. CMOS is prone to high step output overshoot and loads +stray capacitance stability yet C_load are reduced by hFE.
Rs = 1 Ohm means 300 mW dissipation when 100mV will do with 100mV/300mA = 1/3 Ohm or similar with 30 mW. Then change Gain ratio as required.
R6 is redundant relative to R7.
Accuracy depends on tolerance stack-up of all resistors.
For Short circuit protection choose 3V drop R on collector @ 400mA