# Current Limiter Circuit

#### Jammill

Oct 7, 2015
6
Hi i'm trying to create a circuit which would limit the output current @ 1A ,20V by using transistors, i don't know where to start any ideas?

I wil be using Proteus-isis

Last edited:

Jan 25, 2012
255

#### Arouse1973

Dec 18, 2013
5,178
Hi i'm trying to create a circuit which would limit the output current @ 1A ,20V by using transistors, i don't know where to start any ideas?

I wil be using Proteus-isis

Hello Jammill. Can you explain a little more about your application? Welcome to EP BTW.
Thanks

#### Jammill

Oct 7, 2015
6
Hello Adam, i'm doing a project to design design a bench power supply for use in a science laboratory by undergraduate students. Typically they are expecting a bench power supply to cover the following ranges 3.5, 5.0, 9.0, ±15 i have simulated the voltage ranges using regulators now i would like to create an current limiter with an output of 1A

#### Arouse1973

Dec 18, 2013
5,178
Ok so you know that the voltage on the output of the regulator will be 1 Amp * RL. It's just you said you needed 20 Volts at 1 Amp. That means your load can't be lower that 20 Ohms. Does this still apply. Do you have your circuit diagram you have been working on?
Cheers

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,761
@Arouse1973 I believe you may have confused current limiter with current regulator. The OP wants to build bench power supplies with current limiting. So the load can be anything from an open-circuit down to whatever resistance will draw the maximum current specified. The reference that @Miguel Lopez cited is a good start in that direction.

#### Arouse1973

Dec 18, 2013
5,178
@Arouse1973 I believe you may have confused current limiter with current regulator. The OP wants to build bench power supplies with current limiting. So the load can be anything from an open-circuit down to whatever resistance will draw the maximum current specified. The reference that @Miguel Lopez cited is a good start in that direction.

Hi Hop

The OP said he wanted 1 Amp at 20 Volts. I was merely saying that the voltage will drop if he tries to draw more current than this. I guess he knows that. In a bench power supply where you can adjust the output voltage then current limit and regulation could be considered the same thing unless you are talking about fold back limiting which I wouldn't like on a power supply. All current sources in the real world are dependant sources, if they weren't then yes you would have infinite current regulation which would not be what the OP wants.

Thanks

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,761
Hi Hop

The OP said he wanted 1 Amp at 20 Volts. I was merely saying that the voltage will drop if he tries to draw more current than this. ...

Hi Adam... no big deal. You are correct, the voltage will drop if you exceed the current limit. Like most questions here, this one is open to interpretation, especially since we haven't heard back from the OP since you last posted. But I'm with you on so-called "fold back" limiting. Whose bright idea was that? Much prefer a nice smooth transition from constant-voltage mode to constant-current mode rather than a sudden decrease (fold back) in output voltage that makes the power supply behave like a negative-resistance source. I have seen such power supplies break into oscillation because of that behavior, although fortunately I have encountered none this century. Maybe such things are a blast from the past and will never more appear.

All real-world current sources have a maximum compliance voltage, just as real-world voltage sources have a maximum current capability. For an adjustable variable-voltage bench supply, the compliance voltage is the same as the constant-voltage output when current limiting begins. I think this wasn't true for fold-back designs, where the output voltage versus output current actually graphed "backwards" and hence gave the name "fold back" to this kind of current limiting.

#### Jammill

Oct 7, 2015
6
Hey, i managed to figure it out thanks

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