# Current Limited Power Supply

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#### duddface

##### Newbie level 2
Hi All,
I am looking to simulate a current limited power supply to recreate the condition of my power supply being current limited due to load startup transients during my bench tests. Would anyone be aware of any way I can model the current limited power supply in Pspice.I know it is a distant possibility with Micorcap and Intusoft, but my needs are for Pspice.

#### v_c

Are you saying that your source is current limited or are you trying to limit the current that your power supply will output?

If your source is current limited you can just model the source as a thevenin equivalent (voltage source Vth in series with a resistance Rth) and make sure that the short circuit current given by Vth/Rth is your max current.

If you are trying to artificially limit the current out of a power supply, the simplest (but not necessarily the best) way to do this is to put a series resistor with your output. Then take the voltage across this resistor and apply it to the base emitter junction of a BJT. Choose the resistor such that R*Imax=Vbe,on, so at the max current, the BJT will be turned on and collector current will flow. You can then use this current to steer current away from a controlling element. I am assuming you are talking about a linear regulator here -- you did not specify.

You can also do it as shown on Figure 8 here **broken link removed**

Try a google search on "linear regulator current limit" and you will find a lot of information.

Cheers,
$v_c$

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