Finding the right components to achieve proper voltage from power supply

Thread Starter

abu1985

Joined Oct 18, 2015
73
I have 38vdc, I need between 18 and 25vdc (pretty big difference, I know. I also need -18 to -25vdc). There's a few regulators/buck converters to do that, but I also need 3 amps, that's where things get hard. Knocking it down to 24 and finding a chip that also lets me pull up to 3amps is hard to find. Are there other options to get some amperage headroom after a 1 amp regulator? A current buffer comes to mind, but I've never played with any. And "Current Buffer" just sounds like something I would need lol.

This is all in effort to learn and build some audio circuits, but mostly to not spend money on another transformer that would probably better suite the power supply circuit.
 

SamR

Joined Mar 19, 2019
2,260
Good news is that they are cheap and meet the voltage requirement. Bad news is they max out at 1.5A so for 3A I would probably want to use 3 of them in parallel. Also they will need heatsinking and possibly a cooling fan.
 
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Thread Starter

abu1985

Joined Oct 18, 2015
73
Good news is that they are cheap and meet the voltage requirement. Bad news is they max out at 1.5A so for 3A I would probably want to use 3 of them in parallel. Also they will need heatsinking and possibly a cooling fan.
Even with the transistors at the top of the circuit? The data sheet doesn’t say how much that circuit can handle, but the chip alone should handle 1.5a. But I also didn’t think about putting them in parallel...
 

Papabravo

Joined Feb 24, 2006
13,972
Good news is that they are cheap and meet the voltage requirement. Bad news is they max out at 1.5A so for 3A I would probably want to use 3 of them in parallel. Also they will need heatsinking and possibly a cooling fan.
The LM317 does not draw 3 amperes. That current comes through the pass transistors. They probably have a better heatsink than the TO-220 package of the LM317.
 
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MisterBill2

Joined Jan 23, 2018
6,373
Heat sinking is an absolute requirement. And if you have lots of money to spend then some of those links may be OK if you like spending a lot of money. The circuit in post #2 will work, and using two transistors in parallel is a good idea, but you will need to put a resistor in series with each emitter of the pass transistors to tend to equalize the current between the transistors, which is important. And adequate heat sinking is indeed vital.
 
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