# limiting DC current

#### raidermanz

Joined Aug 14, 2007
32
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

#### John Luciani

Joined Apr 3, 2007
477
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 *)

#### raidermanz

Joined Aug 14, 2007
32
Thank you very much.

#### davefromnj

Joined Oct 14, 2008
4
Use a properly rated PTC Thermister in series with the load.