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Looking for a semiconductor circuit breaker

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Plecto

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In my current design I'm taking advantage of the over-current limit feature of a LM317 and using it as a fast acting short circuit protection device. This is a bad solution as the voltage drop across it is too big. I'm wondering if there are dedicated chips for this purpose? A simple two-pin device that cuts current flow if the current gets too big? I need it to act fast so a PTC or polyfuse is not going to work.
 

Hi,

the idea is not new. If there was a simple solution you could buy it.
And the seller makes a lot of money.

Or you find a good solution and become rich.

My answer:
* there is no simple solution
* and the solutions that really work are relatively complicated and need more than two pins.

Klaus
 

Done:

4yHqBEM.png


How can this be complicated? All you need is a sense resistor, fet and control logic? An adjustable regulator does it just fine.
 

Hi,

First: it doesn´t work.

It is not for AC, only for DC.
It is only for low currents.
It doesn´t care about inrush current of capacitove loads or motors.

It has some drawbacks that you didn´t mention in your initial post.
So it can´t replace a usual circuit breaker nor a polyfuse.

Maybe with some modifications it can work for you, but I doubt this will become some kind of "universal" circuit breaker.

***
A regulator can just generate a current limiter (with lot´s of disspated power), but not a latching circuit breaker.

Klaus
 

If you want an efficient implementation with low voltage drop, a two wire solution doesn't work.

How can this be complicated? All you need is a sense resistor, fet and control logic? An adjustable regulator does it just fine.
Click to expand...

Think thoroughly before posting ignorant assumptions. A FET needs several volts Vgs to turn fully on. There must be usually a third power supply wire.

Another problem is with exact device characteristic. Pure current limiting will overheat the switch fast, you need at least thermal shutdown. An useful electronic fuse would implement some kind of latching behavior, but must also handle inrush currents.

Application specific electronic fuse functions are implemented in many systems, but it's difficult to design an universal electronic fuse device.
 

The simple circuit I posted was just to through out an idea, it probably won't work in practice (the shorting zener diode is probably not a great idea). I see that the voltage drop will make this solution unfeasable for a lot of applications, but if one can allow around 1.5V of drop, isn't it perfectly possible to make a two legged electronic fuse?

What other options do I have if I can accept a seperate power input other than to make some fet+mcu or fet+comparator solution? I'm looking at mouser and digi-key, but I'm not really sure what to search for.
 

The question how the current will be sensed ?? There should be a system that surveys this over-current.
It will be a current sense resistor ( voltage drop over on it ) or surveillance of magnetic field over supply line.We know very well the first method, the second is complicated because sensing a weak magnetic field
is pretty difficult.Allegro Microsystems has some solution by using Hall Effect Sensor but this one works at high currents only.
**broken link removed**
 

There are devices for that. See, for example,

**broken link removed**

This is a MOSFET switch which turns off if the current exceeds 5A. It stays turned off until power cycled. On resistance is about 0.130 ohm. It's a MOSFET, so it has on-resistance, not a diode drop.
 

As any other MOSFET, the protected switch needs a sufficient Vgs to turn the MOSFET on. The point has been already discussed in this thread, e.g. in post #5.

Advantages of the mentioned device are full thermal protection and a shut-off latch feature.
 

If you can tolerate a 2.5V minimum voltage drop, there are these new two-terminal constant current linear regulators from Diodes, Inc.

https://www.digikey.com/en/product-highlight/d/diodes/al5809-constant-current-linear-regulator

These are intended for driving LED strings, and come in 15 mA, 20 mA, 30 mA, 40 mA, 50 mA, 60 mA, 90 mA, 120 mA, and 150 mA sizes. They're current limiters, not fuses; they limit the current to the indicated value.

If you can't tolerate a voltage drop, you're going to have to use a 3-terminal device. I'd suggest that 3-terminal protected latching MOSFET above. That plus a resistor is all you need.
 
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    FvM

    FvM

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The Diodes current limiters look promising. If they are actually fail-safe due to inbuilt thermal shutdown, they could work in the higher voltage range like a kind of fast PTC fuse.

I'm not sure if IPS021 and similar protected MOSFET will work as two-terminal device.
 

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