Operating and controlling insulated gate bipolar transistors in high speed failure mode situations
View Patent ↗A circuit and method to provide dynamic fault protection to transistors are disclosed. The fault protection may be particularly suited for protecting insulated gate bipolar transistors (IGBTs).
1. A system to control operation of an insulated gate bipolar transistor, the system comprising:
a detector for detecting a fault state of an insulated gate bipolar transistor (IGBT), the detector including a circuit responsive to an induced voltage across a stray inductance; and
a controller including a first stage and a second stage for controlling and shutting off the IGBT responsive to detection of a fault state, the first stage comprising a negative feedback control unit that is coupled to the induced voltage across the stray inductance and that dynamically controls a rate of change in a fault current based in part on the fault state of the IGBT of the circuit, wherein the induced voltage across the stray inductance is between a Kelvin emitter and a power emitter of the insulated gate bipolar transistor.
2. The system of claim 1 , wherein the first stage controls a rate of change in a fault current for a first interval, and the second stage turns off the IGBT upon expiration of the first interval.
3. The system of claim 1 wherein the detector includes a circuit responsive to a magnitude and a duration of a change in current with respect to time.
4. The system of claim 1 wherein the first stage dynamically controls a rate of change in a fault current based at least in part on the fault state of a circuit and the second stage turns OFF the IGBT at a slower rate than a conventional rate.
5. The system as recited in claim 4 , wherein the rate of change in the fault current is substantially linear.
6. The system of claim 1 , wherein the negative feedback control unit is coupled to a resistor capacitor (RC) network across the stray inductance.
7. The system of claim 6 , wherein the negative feedback control unit dynamically controls a rate of change in the fault current by operating a transistor in a linear range.
8. A method to control operation of Insulated Gate Bipolar transistor (IGBT), the method including the steps of:
detecting a fault state of a transistor with a circuit responsive to an induced voltage across a stray inductance;
dynamically controlling a rate of change in a fault current based at least in part on the fault state for a first interval; and
turning off the IGBT at a desired rate upon expiration of the first interval, wherein the step of detecting the fault state includes detecting the induced voltage across the stray inductance between a Kelvin emitter and a power emitter of the IGBT.
9. The method of claim 8 wherein detecting a fault state of the IGBT includes detecting a magnitude and a duration of a change in current with respect to time.
10. The method of claim 8 wherein dynamically controlling a rate of change in a fault current based at least in part on the fault state includes reducing the fault current to a defined level.
11. The method of claim 8 , wherein the rate of change in a fault current is controlled to provide a linear reduction in fault current to a defined level.
12. The system of claim 8 wherein dynamically controlling a rate of change in a fault current based at least in part on the fault state further includes turning OFF the transistor at a slower rate than a conventional rate.