OVER-VOLTAGE PROTECTION CIRCUIT FOR A DRIVE TRANSISTOR
A drive transistor is connected to a resonant load in a low-side drive configuration. The voltage across the conduction terminals of the drive transistor is sensed and compared to an over-voltage threshold. An over-voltage signal is asserted in response to the comparison. The drive transistor is controlled by a PWM control signal in normal mode. In response to the assertion of the over-voltage signal, the drive transistor is forced to turn on (irrespective of the PWM control signal) to relieve the over-voltage condition. Operation of the circuit may be disabled or forced into soft start mode in response to the assertion of the over-voltage signal. Additionally, the pulse width of the PWM control signal may be reduced in response to the assertion of the over-voltage signal.
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This disclosure relates generally to an over-voltage protection circuit, and more particularly to an over-voltage protection circuit configured to protect a pulse width modulation (PWM) controlled drive transistor.
BACKGROUNDIt is known in the art to provide a low-side drive transistor coupled to a load circuit. For example, the low-side drive transistor may comprise an insulated gate bi-polar transistor (IGBT) and the load circuit may comprise a resonant tank circuit. This circuit configuration is illustrated in
In a number of applications, the IGBT may be damaged as a result of an over-voltage condition. There is a need in the art to protect the IGBT.
SUMMARYIn an embodiment, a circuit comprises: a drive transistor having a control terminal configured to receive a drive signal and having a first conduction terminal and a second conduction terminal, wherein said first conduction terminal is configured for connection to a load circuit; a sense circuit configured to sense a voltage across the first and second conduction terminals; a comparator circuit configured to compare the sensed voltage to voltage threshold and generate a signal indicative of an over-voltage condition; and drive circuitry configured to generate said drive signal in response to a pulse width modulation (PWM) signal, said drive circuit including a force on circuit actuated in response to said signal indicative of the over-voltage condition to force said drive transistor to turn on irrespective of the PWM signal.
In an embodiment, a method comprises: applying a drive signal to a control terminal of a drive transistor including a conduction terminal configured for connection to a load circuit; sensing a voltage across the first and second conduction terminals; comparing the sensed voltage to voltage threshold; generating a signal indicative of an over-voltage condition in response to said comparing; and generating said drive signal in response to a pulse width modulation (PWM) signal, wherein generating further comprises forcing said drive transistor to turn on in response to said signal indicative of the over-voltage condition irrespective of the PWM signal.
In an embodiment, a circuit comprises: a drive transistor having a control terminal configured to receive a drive signal and having a first conduction terminal and a second conduction terminal, wherein said first conduction terminal is configured for connection to a load circuit; a sense circuit configured to sense a voltage across the first and second conduction terminals; a comparator circuit configured to compare the sensed voltage to voltage threshold and generate a signal indicative of an over-voltage condition; a pulse width modulation (PWM) signal generator configured to generate a PWM signal; and a drive circuit configured to generate said drive signal in response to said PWM signal if the signal indicative of an over-voltage condition is not asserted and otherwise force said drive transistor to turn on if the signal indicative of the over-voltage condition is asserted.
For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Reference is now made to
The over-voltage protection circuit 12 includes a resistive divider circuit formed by series connected resistors R1 and R2 and configured to function as a voltage sensor. One terminal of the resistive divider circuit is coupled to the collector terminal of the IGBT 14. The other terminal of the resistive divider circuit is coupled to the reference supply node. Thus, the voltage drop across the resistive divider circuit is equal to (or at least representative of) the voltage drop across the collector and emitter terminals of the IGBT 14 (i.e., the voltage drop equals Vce). The resistive divider circuit includes a tap node 30 at the series connection point of the resistors R1 and R2. The voltage at tap node 30 (V30) is a fraction of the voltage Vce, wherein that fraction is set by the resistance values of the resistors R1 and R2. The voltage V30 is applied to the non-inverting input terminal of a comparator circuit 32. The inverting input terminal of the comparator 32 receives a reference voltage Vref. The comparator circuit 32 compares the voltage V30 to the voltage Vref and generates the OVC signal on line 22 having a logic state responsive to the comparison. In particular, the OVC signal transitions to logic high (i.e., is asserted) when the voltage V30 exceeds the voltage Vref. In a preferred implementation, the comparator circuit 32 is a hysteresis comparator, so the comparison of voltage V30 and Vref leading the state changes for the OVC signal is subject to a built-in hysteresis. The force on circuit 20 operates responsive to assertion of the OVC signal. When the OVC signal is logic high, the force on circuit 20 causes the gate driver circuit 18 to force the drive signal to a logic high state (and thus turn on the IGBT 14) regardless of the state of the received PWM signal.
Reference is now made to
Reference is now made to
OVC signal and forces the gate driver circuit 18 to output a logic high state for the drive signal DS (even though the PWM signal is logic low). This causes the IGBT 14 to turn on and current increases through the IGBT 14. The over-voltage condition is suppressed as the voltage V30 is shown to fall back below the reference voltage Vref in response to the IGBT 14 turning on. Thus occurs prior to the over-voltage rising to exceed either the essential margin set as a function of propagation delay or the maximum limit of the transistor device. When the voltage V30 falls back below the reference voltage Vref, the output of the comparator circuit 32 transitions the OVC signal back to logic low (at time tf) and the force on circuit 20 is deactuated. The gate driver circuit 18 is thereafter once again responsive to the PWM signal.
In the embodiment of
In another embodiment as shown in
In another embodiment as shown in
Reference is now made to
The PWM generator 24 is implemented, in one example, as integrated circuit device, such as a microcontroller. The excessive over-voltage condition detection circuitry 44 may then be implemented on the microcontroller as a mixture of hardware and software. Additionally, the functionalities for the disable circuitry 40 and the soft-start circuitry 42 may be supported by the microcontroller using hardware or a combination of hardware and software.
In an example of the implementation of the systems shown in
It will be readily understood by those skilled in the art that materials and methods may be varied while remaining within the scope of the present disclosure. It is also appreciated that the present disclosure provides many applicable inventive concepts other than the specific contexts used to illustrate embodiments. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacturing, compositions of matter, means, methods, or steps.
Claims
1. A circuit, comprising:
- a drive transistor having a control terminal configured to receive a drive signal and having a first conduction terminal and a second conduction terminal, wherein said first conduction terminal is configured for connection to a load circuit;
- a sense circuit configured to sense a voltage across the first and second conduction terminals;
- a comparator circuit configured to compare the sensed voltage to voltage threshold and generate a signal indicative of an over-voltage condition; and
- drive circuitry configured to generate said drive signal in response to a pulse width modulation (PWM) signal, said drive circuit including a force on circuit actuated in response to said signal indicative of the over-voltage condition to force said drive transistor to turn on irrespective of the PWM signal.
2. The circuit of claim 1, wherein the drive transistor is an insulated gate bi-polar transistor (IGBT).
3. The circuit of claim 1, further comprising said load circuit.
4. The circuit of claim 3, wherein said load circuit is a resonant tank circuit.
5. The circuit of claim 1, wherein the drive transistor is a low-side drive transistor.
6. The circuit of claim 1, further comprising a PWM generator circuit configured to generate said PWM signal.
7. The circuit of claim 6, wherein the PWM generator circuit includes a soft start circuit, and wherein the soft start circuit is actuated in response to said signal indicative of the over-voltage condition.
8. The circuit of claim 6, wherein the PWM generator circuit includes an excessive over-voltage condition detection circuit configured to disable generation of the PWM signal if a number of signals indicative of the over-voltage condition are received in excess of a shut down threshold.
9. The circuit of claim 6, wherein the PWM generator circuit includes an excessive over-voltage condition detection circuit configured to reduce a pulse width of the PWM signal if a number of signals indicative of the over-voltage condition are received in excess of a reduction threshold.
10. The circuit of claim 9, wherein the excessive over-voltage condition detection circuit is further configured to incrementally reduce pulse width of the PWM signal with each reception of the signal indicative of the over-voltage condition in excess of said reduction threshold.
11. The circuit of claim 10, wherein the excessive over-voltage condition detection circuit is still further configured to disable generation of the PWM signal if the number of signals indicative of the over-voltage condition received is in excess of a shut down threshold.
12. The circuit of claim 6, wherein the PWM generator circuit includes a disable circuit configured to disable generation of the PWM signal in response to said signal indicative of the over-voltage condition.
13. A method, comprising:
- applying a drive signal to a control terminal of a drive transistor including a conduction terminal configured for connection to a load circuit;
- sensing a voltage across the first and second conduction terminals;
- comparing the sensed voltage to voltage threshold;
- generating a signal indicative of an over-voltage condition in response to said comparing; and
- generating said drive signal in response to a pulse width modulation (PWM) signal,
- wherein generating further comprises forcing said drive transistor to turn on in response to said signal indicative of the over-voltage condition irrespective of the PWM signal.
14. The method of claim 13, further comprising actuating a soft start process for PWM signal generation in response to said signal indicative of the over-voltage condition.
15. The method of claim 13, further comprising disabling PWM signal generation in response to said signal indicative of the over-voltage condition.
16. The method of claim 13, further comprising disabling PWM signal generation if a number of signals indicative of the over-voltage condition are received in excess of a shut down threshold.
17. The method of claim 13, further comprising reducing a pulse width of the PWM signal if a number of signals indicative of the over-voltage condition are received in excess of a reduction threshold.
18. The method of claim 17, further comprising incrementally reducing pulse width of the PWM signal with each reception of the signal indicative of the over-voltage condition in excess of said reduction threshold.
19. The method of claim 18, further comprising disabling generation of the PWM signal if the number of signals indicative of the over-voltage condition received is in excess of a shut down threshold.
20. A circuit, comprising:
- a drive transistor having a control terminal configured to receive a drive signal and having a first conduction terminal and a second conduction terminal, wherein said first conduction terminal is configured for connection to a load circuit;
- a sense circuit configured to sense a voltage across the first and second conduction terminals;
- a comparator circuit configured to compare the sensed voltage to voltage threshold and generate a signal indicative of an over-voltage condition;
- a pulse width modulation (PWM) signal generator configured to generate a PWM signal; and
- a drive circuit configured to generate said drive signal in response to said PWM signal if the signal indicative of an over-voltage condition is not asserted and otherwise force said drive transistor to turn on if the signal indicative of the over-voltage condition is asserted.
21. The circuit of claim 20, wherein the PWM signal generator comprises a soft start circuit actuated when the signal indicative of the over-voltage condition is asserted.
22. The circuit of claim 20, wherein the PWM signal generator comprises a disable circuit actuated when the signal indicative of the over-voltage condition is asserted.
23. The circuit of claim 20, wherein the PWM signal generator comprises a pulse width control circuit configured to reduce a pulse width of the PWM signal in response to assertion of the signal indicative of the over-voltage condition.
24. The circuit of claim 23, wherein the pulse width control circuit is further configured to incrementally reduce the pulse width of the PWM signal with each assertion of the signal indicative of the over-voltage condition.
Type: Application
Filed: Oct 8, 2014
Publication Date: Apr 14, 2016
Applicants: STMICROELECTRONICS INTERNATIONAL N.V. (Amsterdam), STMICROELECTRONICS S.R.L. (Agrate Brianza)
Inventors: Ranajay Mallik (Ghaziabad), Luigi Abbatelli (Catania), Giuseppe Catalisano (Carlentini (SR)), Akshat Jain (Nahan)
Application Number: 14/509,427