Electronics > Projects, Designs, and Technical Stuff
LM317 control by PWM
Yansi:
So why are you constantly arguing my solution is too complicated, if yours is becoming exactly the same? :)
The discrete solutions would give quite more ways to implement things differently (or even better, if you want).
Zero999:
--- Quote from: Yansi on February 02, 2019, 09:59:37 pm ---So why are you constantly arguing my solution is too complicated, if yours is becoming exactly the same? :)
The discrete solutions would give quite more ways to implement things differently (or even better, if you want).
--- End quote ---
The LM317 does things such as safe operating area and thermal protection which are virtually impossible with a discrete design and is no more complex to implement. The only extra complexity associated with the LM317 is the requirement for a current sink to provide a minimum load, which is just a resistor, two diodes and a low power transistor. This is already less complex than the Darlington pair you're proposing, before any current limiting is added.
Getting an op-amp with a sufficiently high voltage rating is a challenge whichever route you take, but the Darlington pair one is more difficult. The LM317 solution only needs the op-amp's output voltage to reach 1.25V less than the output voltage, whist the Darlington solution requires the op-amp's output to exceed the output voltage by at least 1.6V and most op-amps require a couple of volts headroom.
Yansi:
SOA protection using discrete components is just as easy to implement. What other thing than a current limit following a voltage drop across the pass element would you need? Discrete transistor audio amps solve this SOA protection on common basis. :-//
Thermal protection may become more tricky, depending on the circuit, but again, what more then just a thermal cutoff is needed? Havin a thermal cutoff fuse in the mains input is all what is needed to protect the supply. If it can't cool enough, then it is probably badly designed or would not work anyway (as some dumbass may have covered the heatsinks, etc).
Kalvin:
TI's LM395 "ultra reliable transistor" comes with current limiting, power limiting, and thermal overload protection.
http://www.ti.com/product/LM395/description
It is a complete IC turned into an NPN transistor with extra protection features.
soldar:
Couple of thoughts.
The LM317 uses a resistor to set the output voltage. Could it be replaced by a FET which could be controlled by voltage?
The LM317 uses a resistor to set the output voltage. It would be easier to use a different circuit which uses a voltage reference, like a zener, and then vary that reference voltage.
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