lm317 current regulator question

[thebadtall]

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

 

[barry]

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.

 

[tpetar]

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

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:

 

[IanP]

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:

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

 

[tpetar]

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

 

[thebadtall]

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?

 

[tpetar]

You can use digital pot.


Best regards,
Peter

:wink: