Foldback Current Limiter Circuit and its I-V Characteristics

286

03:39:26

A Foldback Current Limiting circuit provides overcurrent/short-circuit protection by reducing the output voltage AND current in the event of a fault. The benefit of having a low short-circuit current is that the faulty load and the pass transistor don't sustain server damage. Having a low short circuit current helps protect the pass transistor from overheating. The Short-Circuit current is 32mA, and the Knee Current (the current at which it trips) is 72mA.

Wikipedia: https://en.m.wikipedia.org/wiki/Foldback_(power_supply_design)

Source of the circuit: https://electronics.stackexchange.com/questions/299389/how-can-i-calculate-knee-current-for-this-foldback-current-limiter

Later, I will implement this in my 5V regulator circuit and talk about the advantages of this type of current limiting over the traditional constant current type of protection in more detail.

Thanks to kiani for the circuit idea.

published 6 years ago

kiani

6 years ago

That is a nice current limit circuit, thanks for the post.... Btw maybe you don't need the Fet and the Ameter for currenthttp://everycircuit.com/circuit/5729306802913280 limit measurements..chk this....

PrathikP

6 years ago

http://everycircuit.com/circuit/5729306802913280

PrathikP

6 years ago

Ah yes the IV curve looks a lot better now. Thanks.

PrathikP

6 years ago

The current goes down to -6mA. I've added a series resistor to fix that.

kiani

6 years ago

Isn't the current limit 60mA! Reset the sqr. Wave voltage settings,, chk. http://everycircuit.com/circuit/6396521382412288

PrathikP

6 years ago

Hmm. The addition of the resistor seems to make the current limiter kick in at 72mA. Without it, it's 60mA. When I was testing the circuit earlier for a different resistor value, I got a knee current of 56mA.

PrathikP

6 years ago

But math tells me that the knee current is 73.92mA!

PrathikP

6 years ago

Try this. Remove the voltage source at the output. Set the resistor to 100ohm and slowly decrease it. Observe the current. The protection kicks in at ~75mA.

PrathikP

6 years ago

But If you wind the resistance down really fast, the circuit trips at 64mA! This dependence on the rate of change change of o/p current is so odd. Or is it just a simulation bug?

kiani

6 years ago

I think it must be the sim. I tried different sim speeds, things change. irf. Of course the transient overcurrents might not be seen by current limit sensors,, if there are possibilities of such transient overloads then maybe a suppressor of some sort might be used, , however psu.s have capacitors on their o/ps which obsorbs very fast tranient current spikes,, in industry as you know psu.s are designed to cater for different loads and applications.. Its a big industry.

add comment in editor

EveryCircuit is an easy to use, highly interactive circuit simulator and schematic capture tool. Real-time circuit simulation, interactivity, and dynamic visualization make it a must have application for professionals and academia. EveryCircuit user community has collaboratively created the largest searchable library of circuit designs. EveryCircuit app runs online in popular browsers and on mobile phones and tablets, enabling you to capture design ideas and learn electronics on the go.