MOSFET Short Protection

Hello, Does anyone have a good way to protect a MOSFET that is driven by a PIC from a short???

it will be better if u explain ur problem more i was having a problem of MOSFET burning when i was making a PWM driver to control a DC Motor and may i can help u but send more information

You have to build a current detection circuit to limit the maximum current flow through the MOS

I need to find a way to protect the outputs of the mosfets from a short that is resettable and inexpensive OCD's ( Over Current Devices ) cost too much..... thank you

if using a relay is possible in the circuit u can find alot of sort circuit protection using the relay tray to find them and i will search for good circuit to u

Solution of this problem necessiates of carefully studying the application at hand.

One need to know max allowable current load and Vds at that current load. Than with appropriate margin (allowing marging for PVT and opamp offset etc.) one can have a comparator to compare Vds with a set voltage. If Vds drops below that voltage than a short is detected and comparator output used for appropriate action. Appropriate action here for example limiting the current by bang bang control or limiting the current to a preset value or folding back the current or completely shutting the circuit down (most likely more options, but this much at top of my mind now). Basic idea is detecting Vds and if say it is less than Vdsat than deciding there is a short is occured. Of course before starting up the circuit Vds=0 so this kind of circuit application issues also should be considered and proper actions and allowances should be made.

I hope this much info will set you in right direction. Good luck.

so, im thinking that it would be possible to run a feedback line back to the uC PIC16F84 and just include a routine to compaire the output pin of the PIC vs. Output of the MOSFET...... When it detects near 0v on the ouput of the MOSFET then shut down the gate pin...

chevymn1964 said:

so, im thinking that it would be possible to run a feedback line back to the uC PIC16F84 and just include a routine to compaire the output pin of the PIC vs. Output of the MOSFET...... When it detects near 0v on the ouput of the MOSFET then shut down the gate pin...

Click to expand...

it is a good idea but will consume a pin i prefer to do it using an external hardware
simply try to make the output from MOS paththrough a relay befor it goes to the load and make the relay is normaly on and sense the voltage of the load using and gate or just a transistor if zero appear it close the relay
sorry i did not have a picture to explain that but i made this circuit befor and it works great from first time "i used a transistor its base connected to the output and the collector connected to the relay coil and the second pin of the relay coil connected to vdd when zero appear the bjt work as inverter and collector become high and no current pass throgh the relay coil then the relay closed and protect the mos"
i wish i helped u
eng_islam

Hello,

my english is poor but i try to explain one way for solve your problem:

If your Mos is "highside" ( you must to drive the Mos-N with voltage doubler and obtain nearly 10V-12V between Gate-Source), you can measured voltage swing in Vds with O.A and trigged OFF order if Vds>Rds*Idmax.
You can have two stages, one for a rapid deltaVds/dt => quick stop, and a second for overload and slow dVds/dt.
You can also detect thermal parameter.
For a load in "low side" it's easy because you have just to put a small resistor in source path and you measure the voltage on this resistor to obtain a mirror of the current.
I hope to give you some ideas.
regards.

DONALD