Combining the Ampere of two voltage regulator?

Other Hardware General Electronics
41

eloso:
so the regulator can be very hot at 700mA? i almost got skin burned when i touched it. Im using tip42c pnp.

Note that my drawing shows both the regulator and pass transistor on the same heatsink. The idea is for both devices to share the same temperature... that way if the pass transistor gets too hot, it heats the 78xx regulator and trips the thermal protection. The circuit is designed to pass along the current limiting and thermal protection of the 78xx regulator to the pass transistor.

42

It's chosen so that when the load is around 10 amps, the load that the 78xx sees is 1 amp.

With the 78xx flowing just 1amp, the 0.15ohm resistor is providing a voltage of 150mv: how is it going to open up the pnp?

I've been using this circuit for literally decades... believe me, it works.

I am sure it works. You may want to write the manufactures a note so they can rewrite the datasheet.

43

Here one for the OP LM317

LM317.png

44

any idea the required watts of the resistor?

45

Tiny: the voltage across it is 700mv at most.

Here one for the OP LM317

Sounds like high time for them to update their datasheet.

BTW, you can use a n-ch mosfet in place of the npn.