short circuit protection of mosfet and igbt

[venuselectronics]

hi

i have made moffet based relay,and one ig based solid state relay is under developement, can any body show me ,how can i protect these relay from short circuit

venus electronics

 

[Tahmid]

Hi,

In between the MOSFET source and ground insert a shunt resistance (value depends on your current requirement). e.g Saying there is a 10A current requirement for the load, so, let's say we use a 0.01 ohm resistor. So, voltage drop across the resistor will be (according to Ohm's Law) V = IR = 10 * 0.01 = 0.1V.

Use a microcontroller or more simply, comparator or op-amp to detect this. Set a reference and compare the voltage with this.

If your reference is 0.1v, then over 10A, the comparator can turn off the MOSFET or IGBT.

You can say set reference at 0.3v, so whenever current flow is greater than 30A, the circuit turns the switch off.

When there is a short-circuit, current is much greater than the 10A or 30A, so it should be fine.

Take care of shunt power rating. If your current is 10A, voltage across the 0.01R shunt is 0.1V, so power dissipated is P = VI = 0.1 * 10 = 1W, so you should use at least a 2W resistor.

Take a look at this:
#1221679

Hope this helps.
Tahmid.

 

[dick_freebird]

If you know that your pass FET on resistance is fairly well
controlled, and the FET can stand to be run so hard that it
develops a decent Vds at "shorted", then you can look at
Vds in the on state as your sense term. This is "lossless"
where an explicit current sense resistor adds to conduction
losses.

In a MOSFET, Rds(on) goes up with temperature so this is
going to go in the right direction thermally. An IGBT might
head the other way (Vce goes down) and this could make the
short circuit trip-point run away somewhat.

You can also look at failure-to-transition. I got a patent
on a scheme of this nature, once. You have to figure out what
the easiest, most certainly available electrical signature
of a shorted (to what?) fault might be, and grab onto it.

 

[venuselectronics]

sir,
i have also developed circuit of that kind, can yo rectifiy it?,than i will send the scematic of the same, or will you please send yor schematic idea

venus electronics

Added after 14 minutes:

dear tahmid ,

i have seen your schematic for shor circuit protection , you had used shunt resistor

there, is it possible to use shunt for more than 100 amp, i think hall effact sensor is better, accurate, and compact in size, and sir sensing point of short circuit should be on other side of shunt will you please elaborate?

venus electronics

 

[venuselectronics]

dear tahmid

can we use sensefet for shortt circuit proection

venus electronics