IR 2125 High Side Switching

Thread Starter


Joined Mar 21, 2007
I want to design a high side switch which uses IR2125. IR2125 is used to drive a N-Channel Power MOSFET.

I have read the following articles:

Using The Current Sensing IR212X Gate Drive ICs

Programmable High Side Current Switch IR3310/11/12

I am using the same circuit as described in the above articles (bootstrap circuit with high side switching). I am finding it difficult to protect the IGBT (110V DC connected) from short circuit at the output. My IGBT as well as the IR2125 are going bad.

Can someone plz help

Give me a solution


Joined Feb 24, 2006
Tell us something about the load you are switching. To be honest 110 VDC is a very suspicious voltage because it sounds very similar to 110 VAC which is the common household voltage in North America. If you are trying to contol 110 VAC with a MOSFET or an IGBT you are in for some nasty surprises.

Thread Starter


Joined Mar 21, 2007
I am using the following circuit (attached herewith) for high side driving of an IGBT. Details of the circuit are as follows:

1. + HV is 110 V DC from a battery bank.
2. High side Driver Used – IR 2125
3. IGBT Used – IXEH40N120D1 (60Amps/1200V - With HiperFRED )
4. Rg – 39 Ohms / 0.25W
5. Rs – 0.1 Ohm / 2W NIWW

Load is connected between O6 and SGND in the circuit attached – Load is inductive in nature (coil of a contactor with coil resistance approx 300 Ohms). The load i.e., the contactor is located at a distance of approximately 10 meters from this circuit and there is no provision for providing any protection mechanisms or components on the load side.

I have separate power for 110 V DC at +HV and +8V for the IN – input of IR 2125 is derived through a power supply, whose input is again the same 110V DC. I already have a 4.7KOhm/0.25W resistor connected to Ground from IN pin of IR2125, so it is guaranteed that the IN pin is pulled to LOW during start-up.

I am facing the following problem:

Case 1:

When 110V DC is applied first and when the input to IN pin of IR2125 is applied, the IGBT gets the gate pulses from the IR 2125 and the load is switched ON. In this condition, if I short-circuit the load (short the contactor coil), the Gate pulses to the IGBT are switched OFF and ERR pin of IR 2125 goes HIGH, thus indicating a fault and the IGBT gets protected from short-circuit.

Case 2:
If I switch OFF the 110V DC and the voltage at the IN pin,
and then short-circuit the load and if I now switch ON the
110V DC, followed by switching ON the IN voltage, my IGBT
is not getting protected. In this case, all Gate-Emitter-Collector of the IGBT are getting shorted. The tracks on the PCB are also getting damaged in this case.

Case 3:
If I change the load to resistive, i.e., if I connect a 300 Ohms resistance as load and repeat the test as described in the above two cases, the circuit works fine, i.e., the IGBT is protected from short circuit in both the cases 1 and 2.

I have 16 such circuits in one card on the same 110V DC supply i.e., identical 16 circuits for 16 different loads.

Kindly advise, what action to take and how to come out of this problem.


IGBT's are tricky....and easy to blow up if you haven't worked with them before.

I haven't had time to look at your circuit, but the first red flag I see is an inductive load, connected with high impedance leads, and absolutely no snubber network across the device! The overvoltage conditions across the device could easily exceed 1200V and very quickly damage the die.

You really need a floating oscilloscope to look across the collector and emitter of the device. For safety reasons, you can reduce the 110Vdc and any spikes you see will be scaled appropriately.

I will try and analyze your schematic a bit more later and let you know what I find out.

Be careful......I once blew up five IGBT H-Bridges in Parrallel with 800V input voltage......and the resulting explosions was calculated to be more joules than 3 hand grenades.....not a pretty sight!:eek::eek: