lm317 current regulator question

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thebadtall

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Hello , Can you inform me , while using the 317 as current regulator, the resistor dissipates all the power ? Or I can use a trimmer ? (to make a variable current regulator) For instance if set R=1 ohm I out = 1.25A ( Wich a trimmer cannot stand ) Thank you
 

What do you mean "dissipates all the power"? All your output current flows through the resistor, if that's what you mean, so the resistor must be sized accordingly.
 


Hi thebadtall, Hi Barry,

If you insist to use pot you can use wire pot with higher power ratings, see examples:


https://www.tme.eu/en/details/pot30w-100r/wire-single-turn-axial-potentiometers/tt-electronics/#

https://www.tme.eu/en/details/pot60w-100r/wire-single-turn-axial-potentiometers/tt-electronics/#


But I dont recommend this design. Price of this power pots are high and design is in redneck style. :smile:

For some lower currents ok.




See this design :

Adjustable Constant Current Regulator with transistor
Use stronger transistor for higher currents.
**broken link removed**

**broken link removed**



Best regards,
Peter

:wink:
 
tpetar said:
See this design :

Adjustable Constant Current Regulator with transistor
Use stronger transistor for higher currents.
**broken link removed**

**broken link removed**



Best regards,
Peter

:wink:
Click to expand...

Peter, you have to very careful when you suggest circuits like that.

The transistor (BC337) is not a match with the current rating of the LM317.
The whole thing is highly non-linear, that is, for most of the way the potentiometer travels from right-to-left there will be no current flowing what-so-ever, and only when the U (base-emitter) goes close to 0.6V there will be rapid increase in current –

You can test this circuit – but with great caution, and with a transistor rated for I(c)>2A

:wink:
IanP
 
Hi IanP,

Yes I agree. In text description is mentioned current up to 500mA, for higher current to use stronger transistor.

For sure testing first.


Best regards,
Peter
 
Hello everyone and thank you ! Thank you Peter for giving me always a solution with a schematic ! I will try that using a 2n3055.
In that way, is it possible to trigger the base of the transistor using an output of atmega8?
 

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