"Self-Healing" 12V 30A Circuit

[Nabors]

I've been working on a small personal project for an accessory control board for my car. One thing I want to incorporate is what one company calls "self-healing" over-current circuit. On a picture they posted of their circuit board, it looks like they are using a SMT device which is a little bigger than a DFN-8 MOSFET. I initially thought it was a PTC, but nothing in a SMT package is remotely high enough current.

 

[BradtheRad]

An article about self-healing circuits suggests it's for complex systems with sensors that detect a problem growing, and re-route or shut down affected paths in time to avoid catastrophic failure.

Your devices don't look like they can carry 30A. No doubt they're control circuitry.

Fuses are easy to use. You can put in additional work on circuit protection by making a current limiter, but then you must decide what makes it release. Do you prefer to (a) cut power and restart?
Or (b) do you want it to monitor current draw during the fault and restore to normal levels when the fault is fixed?

If option B then you must design protection circuitry which is customized for your project and its power levels. That is akin to self-healing but it requires a lot of knowledge and effort.

 

[ZASto]

In your picture, the 8 pin device looks like a MOSFET. It even nas a series resistor to Gate. And element next to it could be shunt resistor for current measuring. You should trace where tht small gate resistor is connected to, to find control circuit.

 

[Nabors]

Thank you for your replies. I have found the Allegro Microsystems Hall-Effect 7-- series current sensors. Could I just run a loop in my programming to monitor each current output and shut the MOSFET off when it's over the specified value? Then in this case, I could add a traditional SMT fuse on each circuit as a backup in case the processor doesn't respond in time.

 

[schmitt trigger]

Sort answer: yes.
Actually, If you are using a microcontroller, you can design "smart" algorithms, such as:

-Ignore very short overloads
-Attempt a restart only if the overload is below xx percent overcurrent. Otherwise, latch up immediately.
-Attempt a limited number of re-starts, before it locks up for good.
-whatever else you can come up with.............

And indeed, a fuse is always a backup of last resort when everything else fails.

 

[Nabors]

I found out that the device in question is a 100V/30A Schottky Barrier Diode, part #Z5TPK30100H. I'm having trouble what a Schottky diode would achieve in this situation?

 

[FvM]

You might have get better answers if you showed the full circuit along with a specification or product link. It won't be bad if the component markings are readable.

Schottky diode can't carry 30A continuously without additional cooling, it can be hardly in the main current path. May be a free-wheeling diode for the MOSFET switch.