Circuit for driving a semiconductor element

Abstract

A drive circuit is provided for driving a voltage-driven semiconductor element by producing a drive signal depending upon an input signal. The drive circuit comprises an output stage and a current-suppressing circuit. The output stage includes two semiconductor elements connected in series. The voltage-driven semiconductor element is connected to a common connection point of the two semiconductor elements. The current-suppressing circuit controls one of the two semiconductor elements to provide an output current flowing through either one of the two semiconductor elements if a voltage applied to the voltage-driven semiconductor element reaches a limit level, which is in excess of a level for conducting the voltage-driven semiconductor element by a predetermined voltage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a circuit diagram illustrating a drive circuit according to a first embodiment of the present invention;

FIGS. 2A and 2B are waveform diagrams illustrating an output current of the drive circuit and gate signal developed in the first embodiment;

FIG. 3 is a circuit diagram illustrating a drive circuit according to a second embodiment of the present invention;

FIG. 4 is a circuit diagram illustrating a drive circuit according to a third embodiment of the present invention;

FIG. 5 is a circuit diagram illustrating a conventional drive circuit;

FIG. 6 is a circuit diagram illustrating another conventional drive circuit;

FIGS. 7 and 8 are waveform diagrams illustrating an output current and a gate signal developed in the conventional drive circuit when R5 is 180 Ω; and

FIGS. 9 and 10 are waveform diagrams illustrating an output current and a gate signal developed in the conventional drive circuit when R5 is 2 kΩ;

FIG. 11 is a circuit diagram illustrating a drive circuit according to a fourth embodiment of the present invention;

FIG. 12 is a circuit diagram illustrating a drive circuit according to a fifth embodiment of the present invention; and

FIG. 13 is a circuit diagram illustrating a further conventional drive circuit.

Claims

1. A drive circuit for driving a voltage-driven semiconductor element by producing a drive signal depending upon an input signal, the drive circuit comprising: an output stage that includes two semiconductor elements connected in series, the semiconductor element that is to be driven being connected to a common connection point of the two semiconductor elements; anda current-suppressing circuit that controls one of the two semiconductor elements to provide an output current flowing through either one of the two semiconductor elements if a voltage applied to the voltage-driven semiconductor element reaches a limit level which is in excess of a level for conducting the voltage-driven semiconductor element by a predetermined voltage.

2. The drive circuit according to claim 1, wherein: the voltage-driven element is a N-channel MOSFET; andthe current-suppressing circuit includes a transistor for suppressing the current whose one output terminal is connected to the input terminal of one of the two semiconductor elements that is connected to a power source side, and whose other output terminal is grounded, anda bias circuit that renders the transistor for suppressing the current to be conductive if the voltage applied to the MOSFET reaches the limit level.

3. The drive circuit according to claim 2, wherein the current-suppressing circuit is connected between the common connection point of the two semiconductor elements and a ground, and also operates as a clamp circuit for clamping the voltage applied to the MOSFET to the limit level.

4. The drive circuit according to claim 3, wherein the clamp circuit executes a clamping operation by utilizing a constant voltage generated across an input terminal and an output terminal of the transistor for suppressing the current if the transistor for suppressing the current is rendered conductive.

5. The drive circuit according to claim 4, wherein the clamp circuit includes a resistor connected between the input terminal of the transistor for suppressing the current and the ground.

6. The drive circuit according to claim 4, further comprising: a Zener diode connected between the input terminal of the transistor for suppressing the current and the ground, the Zener diode having a Zener voltage higher than a constant voltage generated by the transistor for suppressing the current.

7. The drive circuit according to claim 2, further comprising: a Zener diode connected between the MOSFET and the ground and having a Zener voltage higher than the limit level.

8. The drive circuit according to claim 1, wherein: the voltage-driven element is a P-channel MOSFET; andthe current-suppressing circuit includes a transistor for controlling the current connected between an input terminal of one of the two semiconductor elements connected to a ground side and a ground, anda bias circuit that renders the transistor for suppressing the current to be conductive if the voltage applied to the MOSFET reaches the limit level.

9. The drive circuit according to claim 8, wherein the bias circuit includes: a current mirror circuit that forms a mirror pair together with the transistor for controlling the current; anda trigger transistor for supplying a base current to the current mirror circuit if the applied voltage varies to the limit level.

10. The drive circuit according to claim 9, wherein the current-suppressing circuit is connected between a power source and the common connection point of the two semiconductor elements to operate as a clamp circuit for clamping the voltage applied to the MOSFET to the limit level.

11. The drive circuit according to claim 10, wherein the clamp circuit effects a clamping operation by utilizing a constant voltage generated across the input terminal and the output terminal of the trigger transistor if the trigger transistor is rendered conductive.

12. The drive circuit according to claim 11, wherein the clamp circuit includes a resistor connected between the power source and the trigger transistor.

13. The drive circuit according to claim 11, further comprising: a Zener diode connected among a power source, an input terminal of the trigger transistor and the ground, the Zener diode having a Zener voltage higher than a constant voltage generated by the trigger transistor.

14. The drive circuit according to claim 8, further comprising: a Zener diode connected between a power source and the MOSFET and having a Zener voltage higher than the limit level.

15. A drive circuit for driving a voltage-driven semiconductor element having a conduction control terminal depending upon an input signal, the drive circuit comprising: a constant current source for supplying a constant current;a resistor supplied with the constant current depending upon the input signal;a mirror pair on an output side for determining a current flowing through the conduction control terminal of the semiconductor element; anda constant voltage element connected between the conduction control terminal and a potential point that becomes equal to the terminal voltage of the resistor on a current path on a side of a main transistor that forms the mirror pair on the output side, the constant voltage element forming a negative feedback path for a current that flows through the conduction control terminal,wherein the constant current source includes a circuit that is operable independently of temperature and voltage, and the resistor is operable independently of temperature.

16. The drive circuit according to claim 15, wherein: the output stage includes two semiconductor elements connected in series, and the conduction control terminal of the voltage-driven semiconductor element is connected to a common connection point of the two semiconductor elements; andone of the two semiconductor elements in the output stage is a sub-transistor that forms the mirror pair on the output side.

17. The drive circuit according to claim 15, wherein a potential point is disposed between a main transistor that forms the mirror pair on the output side and a sub-transistor that forms the mirror pair for determining a current that flows through the main transistor based on the constant current source.

18. The drive circuit according to claim 17, wherein: the resistor is connected in series with the main transistor that forms the mirror pair on an input side the state of conduction of which varies depending upon a change in the input signal; andthe sub-transistor that forms the mirror pair on the output side is disposed between the main transistor that forms the mirror pair on the output side and the sub-transistor that forms the mirror pair for determining the current.

19. The drive circuit according to claim 18, wherein the mirror pair on the input side includes MOSFETs, and the resistor is connected to the source side of the MOSFETs.