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LM317 Adjustable 20V, 1.5A Supply with Simple SMPS Tracking Preregulator 2015-04-14

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crutschow

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crutschow submitted a new article:

LM317 Adjustable 20V, 1.5A Supply with Simple Tracking Preregulator - LM317 Power supply with switching tracking prereg for good efficiency and minimal heat sink reqmts.

The LM317 is a commonly used, rugged linear regulator with an adjustable output but suffers from the normal inefficiency of linear regulators which can require a large heatsink for the higher output currents, especially if input to output voltage drop is high.
To minimize this, a tracking, switching preregulator can be used to keep the voltage drop across the LM317 essentially constant, at a voltage slightly above the minimum required (3V) for proper regulator operation. This increases...

Read more about this article...
 
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Wow, Nice trick! I am using the 1st part of the circuit designed by you
here
, to charge my cell phone. So it's interesting to me. My cellphone takes maximum 750mA current through it and MOSFET needs medium size heatsink though.)

I guessed heat dissipation is divided into two part (minimised too around switching area)- around MOSFET little and around LM317 chip. To save component (I think LM317 is expensive than TL431) we could totally remove the LM317, and could add a TL431 based adjustable regulator circuit as a reference voltage for LM393, couldn't we?

After that our output part would be the the P-MOSFET. After that I cannot assume its heat dissipation though. (But I know that it would be a noisy power supply with huge ripples!)
 
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Hi cruts,

You do some stuff.

The ciruit is fine as is, of course. I was just thinking: At the moment you have a buck pre reg. Have you thought about another version with s SEPIC pre reg. That way the supply volts could be anything, within reason. I only ask because it would be ideal for an application I have in mind.
 
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