I plan on using the LT3080 to regulate a variable 1-36V 7A DC power supply. This regulator by itself will not provide more than an amp or so, so I will have to use an external series pass transistor per the recommendation in their datasheet:
Now, I am sure this will work fine, however the recommended BJT is expensive, something like $7 a piece. Given I am planning to make a few of these regulator boards, I would like to keep the cost down by choosing a comparable part. This is where I need help.
On Mouser I see plenty of PNP BJTs that support 100v emitter-collector, and 10s of amps for 60 cents, but I don’t know if that will work. So what parameters should I be looking for in the datasheet that would be suitable in this application? It would be great if you can also explain why this part was chosen in the first place and why it is more expensive than other seemingly similar BJTs.
For further clarification, the LT3080 is set to always be a fixed value below the input voltage. This dropout voltage will be maximum 5V. This is to give enough headroom for regulation as well as to account for the voltage drop across the transistor.
What I’m planning to build is meant to suppress ripple and switching noise in a switch mode lab power supply with adjustable current. LT3080 is thus used as a post-regulator for cleaning up the supply rails.
and here's the full version I was playing with earlier with supposedly better ripple suppression.
I'm not experienced in designing circuits (software engineer by profession), so if I'm doing some obvious mistakes please let me know.