Electronics > Beginners
Quick/dirty adjustable PSU from 24V SMPS
lordvader88:
I have a nice 24V SMPS from a printer, that I want to use to power a pass BJT supply, for as wide a range as possible. I only want a few hundred milliamps, just for little quick breadboard use, and it will fit on a 5x7cm pref-board.
Should I heatsink a 2n3055 for say 0.5A at say 22V ?
So I could use a TL431 or overkill LM317 to drive the BJT. Should I use 2N3055 or the PNP version ?
And should I have a small resistor, from the regulator output, to the BJT base ? I assume I should put a small cap on the base. So that would make an RC filter.
Gyro:
--- Quote from: lordvader88 on April 04, 2019, 06:42:08 pm ---I have a nice 24V SMPS from a printer, that I want to use to power a pass BJT supply, for as wide a range as possible. I only want a few hundred milliamps, just for little quick breadboard use, and it will fit on a 5x7cm pref-board.
Should I heatsink a 2n3055 for say 0.5A at say 22V ?
So I could use a TL431 or overkill LM317 to drive the BJT. Should I use 2N3055 or the PNP version ?
And should I have a small resistor, from the regulator output, to the BJT base ? I assume I should put a small cap on the base. So that would make an RC filter.
--- End quote ---
Which is it? :-\
2V drop at 0.5A is 1W, a bare TO3 pkg is probably sufficient.
EDIT: Plenty of simple options... https://duckduckgo.com/?q=2n3055+regulator&atb=v145-4__&iax=images&ia=images
lordvader88:
Oh right, it's Vce*Ic. So 10W if I had 4V@0.5A output with npn. Either way that won't matter much, I can put an old CPU heatsink on it if needed.
Zero999:
--- Quote from: Gyro on April 04, 2019, 07:45:13 pm ---
--- Quote from: lordvader88 on April 04, 2019, 06:42:08 pm ---I have a nice 24V SMPS from a printer, that I want to use to power a pass BJT supply, for as wide a range as possible. I only want a few hundred milliamps, just for little quick breadboard use, and it will fit on a 5x7cm pref-board.
Should I heatsink a 2n3055 for say 0.5A at say 22V ?
So I could use a TL431 or overkill LM317 to drive the BJT. Should I use 2N3055 or the PNP version ?
And should I have a small resistor, from the regulator output, to the BJT base ? I assume I should put a small cap on the base. So that would make an RC filter.
--- End quote ---
Which is it? :-\
2V drop at 0.5A is 1W, a bare TO3 pkg is probably sufficient.
--- End quote ---
I thought he wanted it to be adjustable. The maximum power dissipation depends on the current, at the minimum output voltage.
The LM317 alone will probably do, as long as it's on a big heat sink.
Gyro:
That's why I highlighted the two conflicting passages and asked the question!
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