Power supply current limiter

[Vince_Game]

Hi! I want to know how to add a current limiter to a psu that turns on an LED when the current goes over an adjustable limit.

Vince

 

[MrAl]

Hi,

What kind of power supply is it, or do you want to add it externally?

 

[Vince_Game]

I am making a 0-30 V supply for a school project.

I'm not sure what I will use to regulate it yet. AFAIK there are several ways to do it:

LM317
L200
LM723 with external transistor
Opamps circuits
etc.

I understand how these work internally for voltage (and current) regulation, but I cant figure out how to add the CC mode LED that I've seen on some supplies.

 

[ronv]

Without a negitive supply it is hard to get the output voltage or current to 0 with these because all you have to work with is the reference pin. The L200 datasheet has a schematic if close is good.

 

[MrAl]

Hello again,

The 723 has a built in transistor for current limiting, but it is not as accurate as we need sometimes. The question then becomes, just how accurate do you need to set the current and how stable does it have to be with temperature?

The LM317 can regulate current down to 1.25v with a little external circuitry, but again the question is how accurate do you need to set the current?
You can also get the regulation down to 0.000v with a little trick, if you can stand to loose around two diode drops from your main power supply.

So the question you need to think about is just how accurate do you need to set the current, and how stable does it have to be with temperature...
ie very stable, somewhat stable, not too stable, and what do you intend to use the power supply for...small stuff like LEDs or large stuff like charging batteries. The circuit depends a lot on these criteria, as the number of parts goes up with the more accuracy and stability you need.

 

[CafeLogic]

Please clarify what you want by choosing a number from each category:

Type of PSU:

1) PSU maintains a constant voltage so long as current limit not exceeded
2) PSU tries to maintain constant current output


Type of Current limit:

1) Current exceeds an adjustable limit, LED turns on, current is not capped
2) Current is capped at adjustable limit, power supply stays on but reduces voltage or does pwm so that current limit can not be exceeded, LED truns on
3) Current exceeds an adjustable limit, power supply cuts off until reset, LED turns on