All About Circuits Forum limiting DC current
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#1
08-16-2007, 02:54 PM
 raidermanz Junior Member Join Date: Aug 2007 Posts: 32
limiting DC current

I am new to the electronics world, so please forgive my ignorance, I have a mechanical design background so please respond in "little steps"

I have a heating element which will be powered by a 24vdc power supply, at this time, I am not sure what max current I will be getting, however for this question, let's assume that I have 2A available to the heater. From this same power supply, I would like to power an assortment of low consumption devices. My heater is such that it pulls as much current as I can provide to it when it is below it's rated temperature, and the current draw reduces proportionately as the temperature of the device climbs. I would like to limit the maximum current to the heater to 1.5A.

I am probably missing an obvious solution, but please refer to the first sentence of my post.

Thank you for any and all suggestions
#2
08-16-2007, 03:02 PM
 John Luciani Senior Member Join Date: Apr 2007 Location: Massachusetts Posts: 477

Quote:
 Originally Posted by raidermanz I have a heating element which will be powered by a 24vdc power supply, at this time, I am not sure what max current I will be getting, however for this question, let's assume that I have 2A available to the heater. From this same power supply, I would like to power an assortment of low consumption devices. My heater is such that it pulls as much current as I can provide to it when it is below it's rated temperature, and the current draw reduces proportionately as the temperature of the device climbs. I would like to limit the maximum current to the heater to 1.5A.
Take a look at the TI TL431 datasheet. There is a current limiter circuit and a current
sink circuit. Each circuit consists of a TL431, 2 resistors and q power transistor.
Either circuit will work in your application. Make sure you calculate the power
dissipation of the high current resistor and power transistor.

(* jcl *)

Last edited by hgmjr; 08-16-2007 at 11:51 PM. Reason: Repaired quote box
#3
08-16-2007, 03:04 PM
 raidermanz Junior Member Join Date: Aug 2007 Posts: 32

Thank you very much.
#4
08-16-2007, 08:58 PM
 mrmeval Senior Member Join Date: Jun 2006 Posts: 833

LM317 can be configured as a current limiter.
http://www.national.com/ds/LM/LM117.pdf

And this is interesting, look for current regulator circuits.
http://www.instructables.com/id/ERVL...31U3/?ALLSTEPS

Last edited by mrmeval; 08-16-2007 at 09:01 PM.
#5
10-16-2008, 09:05 PM
 davefromnj New Member Join Date: Oct 2008 Posts: 4

Use a properly rated PTC Thermister in series with the load.

 Tags current, limiting

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