IGBT emitter current sensing for early desaturation detection and short circuit protection
A gate driver system includes a gate driver having a first input for receiving a digital input signal, a second input for receiving a short circuit protection signal, and output for driving a power device; a current reconstruction circuit having a first input for receiving a voltage across an inductance associated with the power device, a second input for receiving a current associated with the power device, a third input for receiving the digital input signal, and an output for providing a sensed power device current; and a comparator having a first input coupled to the output of the current reconstruction circuit, a second input coupled to a reference, and an output coupled to the second input of the gate driver.
1. A gate driver system comprising:
a gate driver having a first input for receiving a digital input signal, a second input for receiving a short circuit protection signal, and an output for driving a power device;
a current reconstruction circuit having a first input for receiving a voltage across an inductance associated with the power device, a second input for receiving a current associated with the power device, a third input for receiving the digital input signal, and an output for providing a sensed power device current; and
a comparator having a first input coupled to the output of the current reconstruction circuit, a second input coupled to a reference, and an output coupled to the second input of the gate driver.
2. The gate driver system of claim 1 , wherein the current reconstruction circuit comprises a calibration circuit for determining an inductance value associated with the power device.
3. The gate driver system of claim 2 , wherein the calibration circuit is also configured for determining a resistance value associated with the power device.
4. The gate driver system of claim 3 , wherein the current reconstruction circuit comprises:
a summing circuit having a first input coupled to the first input of the current reconstruction circuit, a second input, and an output;
an integrator circuit coupled to the output of the summing circuit;
a divider circuit having a first input coupled to the output of the integrator circuit, a second input for receiving the inductance value from the calibration circuit, and an output coupled to the output of the current reconstruction circuit; and
a multiplier circuit having a first input coupled to the output of the current reconstruction circuit, a second input for receiving the resistance value from the calibration circuit, and an output coupled to the second input of the summing circuit.
5. The gate driver system of claim 3 , wherein the calibration circuit comprises:
a summing circuit having a first input for receiving a first voltage from the first input of the current reconstruction circuit, a second input for receiving a second voltage from the first input of the current reconstruction circuit, and an output;
an integrator circuit having an input coupled to the output of the summing circuit, and an output;
a first divider circuit having a first input coupled to the output of the integrator circuit, a second input coupled to the second input of the current reconstruction circuit, and an output for providing the inductance value; and
a second divider circuit having a first input for receiving the second voltage from the first input of the current reconstruction circuit, a second input coupled to the second input of the current reconstruction circuit, and an output for providing the resistance value.
6. The gate driver system of claim 5 , wherein the first voltage from the first input of the current reconstruction circuit comprises a voltage corresponding to a positive change in current through the inductance and the resistance.
7. The gate driver system of claim 5 , wherein the second voltage from the first input of the current reconstruction circuit comprises a voltage corresponding to a zero change in current through the inductance and the resistance.
8. The gate driver system of claim 1 , wherein the current reconstruction circuit further comprises a slow overload detection circuit.
9. The gate driver system of claim 8 , wherein the slow overload detection circuit comprises a first input coupled to the output of the current reconstruction circuit, a second input coupled to the third input of the current reconstruction circuit, and an output for providing a slow overload detection signal.
10. The gate driver system of claim 9 , wherein the output of the slow overload detection circuit is coupled to the comparator of the current reconstruction circuit.
11. The gate driver system of claim 9 , wherein the slow overload detection circuit is configured for generating the slow overload detection signal when current sensed power device current values are greater than previous sensed power device current values.
12. A gate driver system comprising:
a power device including a resistance and an inductance;
a gate driver having a first input for receiving a digital input signal, a second input for receiving a short circuit protection signal, and an output for driving the power device;
a current reconstruction circuit having a first input for receiving a voltage across the resistance and the inductance, a second input for receiving a current associated with the power device, a third input for receiving the digital input signal, and an output for providing a sensed power device current; and
a comparator having a first input coupled to the output of the current reconstruction circuit, a second input coupled to a reference, and an output coupled to the second input of the gate driver.
13. The gate driver system of claim 12 , wherein the current reconstruction circuit comprises one or more of a calibration circuit for determining a resistance value of the resistance and an inductance value of the inductance, a slow overload detection circuit and an integrator circuit.
14. The gate driver system of claim 12 , wherein the power device comprises a four-terminal device comprising a first current terminal, a second current terminal, a Kelvin current terminal, and a control terminal.
15. The gate driver system of claim 12 , wherein the current reconstruction circuit comprises a slow overload detection circuit and wherein the slow overload detection circuit comprises a lookup table for storing sensed power device current values.
16. A method of operating a power device, the method comprising:
measuring a voltage across an inductance associated with the power device;
measuring a current associated with the power device;
integrating the voltage across the inductance to provide an integrated value;
dividing the integrated value by an inductance value of the inductance to provide a sensed power device current; and
turning off the power device if the sensed power device current is greater than a reference current.
17. The method of claim 16 , further comprising determining the inductance value of the inductance associated with the power device from the measured voltage across the inductance associated with the power device and the measured current associated with the power device.
18. The method of claim 16 , further comprising measuring a voltage across a resistance in series with the inductance associated with the power device.
19. The method of claim 18 , further comprising determining a resistance value of the resistance.
20. The method of claim 16 , wherein measuring the voltage across the inductance associated with the power device comprises measuring at least the voltage at a Kelvin current terminal of the power device.