In need of voltage regulator help. (Pass transistor)

[Zanderist]

I haven't been able to find any Voltage Regulator ICs that can handle currents greater than 10 amps.

What I'm seeking with this thread is information on pass transistors. Basically how to calculate the values needed.

As a general idea of what I'm trying to accomplish, would it be possible to make something like the LM317 (MAX CURRENT 1.5A) or the LM338 (MAX CURRENT 5 A) be capable of handling up to 20 to 30 amps?

 

[esp1]

hi,
Look at this link.
http://www.reuk.co.uk/LM317-High-Current-Voltage-Regulator.htm

I Googled: pass transistor with LM317

E

 

[chuckey]

Do not use these circuits there is an error on all of them, The 220 ohm resistor should be connected from the output back to pin 1 (voltage setting pin). I can't see the point of the diode, it just puts in an added voltage drop.
Also when using transistors in parallel, a small resistor MUST be put in series with each emitter, to make sure thee total current is shared equally between all the transistors (.1 ohm?).
It is interesting that 99.9 % of the circuits found with Google DO NOT compensate for the Vbe drop of the series transistor as the load current is changed.
This one is as good as any, but it still needs .1 ohm resistors in the emitters of the power transistors. :-
**broken link removed**
Frank

 

[betwixt]

I agree with Frank.

The other problem with 'emitter follower' current boosters is a short or reverse voltage at the output can damage the pass transistors. You must ensure that under short circuit conditions, the base current of the pass transistor is not exceeded as the regulator IC will attempt to drive it as hard as it can.

The circuits with the transistor bases fed from the input of the regulator ("wrapped around" the regulator) are inherently protected by the ICs own protection mechanisms. If the IC shuts down from overheating or overload, it's input current drops and the transistors turn off.

There is no substitute for a properly designed feedback mechanism to stabilize the output voltage and provide overload protection I'm afraid.

Brian.

 

[BigBoss]

Connect 2 Regulators in parallel with the same REF voltage..
Simple..

 

[Audioguru]

Look at this link.
http://www.reuk.co.uk/LM317-High-Current-Voltage-Regulator.htm
I Googled: pass transistor with LM317E

It has a few very stupid mistakes:

 

[crutschow]

Connect 2 Regulators in parallel with the same REF voltage..
Simple..

Simple in concept. But not with common regulators that have an internal reference, such as the LM317. With those you need to add equalizing resistors to avoid current hogging (which impairs the voltage regulation). That's why one regulator with added current booster transistors is usually better.

 

[Zanderist]

Would the formulas found for the 78xx series be relevant to use(as seen in second post of thread)?

https://www.edaboard.com/threads/269905/

 

[betwixt]

Yes, it makes little difference whether the regulator is fixed or adjustable.

Brian.