JP2000307398A - Protection circuit for semiconductor switch device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent thermal destruction of a semiconductor switch element that is a component of a semiconductor switch device. SOLUTION: A protection circuit 1 consists of a current sensor resistor 2 that is connected between the source of a power MOSFET 14 and one output terminal 15b and an npn gate control transistor(TR) 3 that becomes conductive when the voltage drop across the current sensor resistor 2 exceeds a given voltage. Since the current sensing resistor 2 has a positive temperature coefficient, the resistance of the current sensor resistor 2 increases as the temperature rises and the voltage applied between the base and an emitter of the gate control TR 3 also increases. Consequently, the gate voltage of the power MOSFET 14 decreases to suppress the drain current. Since the power consumption of the power MOSFET 14 is reduced, the drain breakdown voltage can be made higher so as to prevent thermal destruction of the power MOSFET 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for a semiconductor switch device in which the output terminals are switched between a conductive state and a non-conductive state by a semiconductor switching element such as a power MOSFET or an IGBT which is turned on / off in response to a control signal. is there.

[0002]

2. Description of the Related Art Conventionally, as a semiconductor switch device 10 'of this type, a light emitting diode 11 which is turned on / off by a control input as shown in FIG.
A photovoltaic element 12 such as a solar cell that receives light from the light emitting diode 11 and generates photovoltaic power, and a semiconductor switching element (power MOSFET) that switches the output terminals 15a and 15b between a conductive state and a non-conductive state. ) 14
And a control circuit 1 for controlling a gate voltage of the power MOSFET 14 according to a photovoltaic voltage generated by the photovoltaic element 12.
And a chip 1 on which the light emitting diode 11 is formed.
6a, a chip 16b on which a photovoltaic element 12, a control circuit 13 and a protection circuit 1 'described later are formed, and a power MO
There is a semiconductor relay called a so-called photo MOS relay in which a chip 16c on which the SFET 14 is formed is mounted in one package. Here, the power MOSFET 14
Is an enhancement type (normally-off type),
When the gate voltage is zero, the drain current does not flow and the device is off. The control circuit 13 has a function of discharging the residual charge accumulated in the gate capacitance of the power MOSFET 14 in a short time when the power MOSFET 14 is turned off, and shortens the time required for turning off the power MOSFET 14. It is. When the photovoltaic power of the photovoltaic element 12 is applied, the control circuit 1
3 is in a high impedance state between the output terminals, and the power M
The gate capacitance of the OSFET 14 is charged efficiently.

In such a semiconductor switch device 10 ′, if an excessive current is applied between the drain and the source of the power MOSFET 14, the power MOSFET 14 is destroyed. It is required to limit the drain-source current. Therefore, as a protection circuit 1 'for limiting the current between the drain and source of the power MOSFET 14, a current detection resistor 2' connected between the source of the power MOSFET 14 and one output terminal 15b and a current detection resistor 2 ' A device having an npn-type gate control transistor 3 that is turned on when a generated voltage drop exceeds a predetermined voltage has been proposed. Here, in the gate control transistor 3, the current detection resistor 2 'is connected between the base and the emitter, and the collector is the power M.
It is connected to the gate of OSFET14. Therefore, when an excessive voltage is applied to the drain of the power MOSFET 14 due to a load short circuit or the like, the current detection resistor 2 ′
, The gate control transistor 3 is turned on, and the gate-source voltage of the power MOSFET 14 is reduced to a constant value.
14 is protected. That is, the power MOSF
Since the ET 14 limits the drain-source current in a region where the gate-source voltage is low, the protection circuit 1 ′ protects the power MOSFET 14 by suppressing the drain current Ids to a constant value as shown in FIG. You can do it.

[0004]

By providing the protection circuit 1 'as described above, the power M of the semiconductor switch device 10 is increased.
Although the withstand voltage of the drain voltage of the OSFET 14 can be improved, the power consumed by the power MOSFET 14 (= drain-source voltage Vds × drain current Ids) increases when the drain voltage Vds increases. Power MOSF due to heat generation of the element itself
The ET 14 may be thermally destroyed. Further, the current detection resistor 2 ′ constituting the protection circuit 1 ′ is connected to the chip 16.
Since the diffusion resistance is a diffusion resistance formed by diffusing impurities into the semiconductor substrate surface b, the resistance value has a negative temperature coefficient. That is, as the temperature rises due to the heat generated by the power MOSFET 14, the resistance value of the current detection resistor 2 'decreases, and the voltage across the current detection resistor 2' decreases.
The voltage applied between the base and the emitter of the gate control transistor 3 decreases. As a result, the power MO
Since the gate voltage of the SFET 14 increases, the drain current Ids increases, further increasing the power consumption, and the power MOSFET 14 is easily damaged thermally.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a protection circuit for a semiconductor switch device that can prevent thermal destruction of a semiconductor switching element included in the semiconductor switch device. Is to provide.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a protection circuit for a semiconductor switch device in which a semiconductor switching element that is turned on and off in response to a control input switches between a conductive state and a non-conductive state between output terminals. At
A current detection resistor connected between one end of the semiconductor switching element and one output terminal; and a gate control transistor for controlling a gate potential of the semiconductor switching element in accordance with a voltage drop generated in the current detection resistor, It is characterized by using a resistor with a positive temperature coefficient as the detection resistor, and when an excessive voltage is applied to the semiconductor switching element and the element temperature rises, the voltage drop that occurs in the current detection resistor increases, thereby increasing the gate. Since the gate potential of the semiconductor switching element is reduced by the control transistor, the current flowing through the semiconductor switching element can be suppressed. As a result, it is possible to increase the maximum voltage at which the semiconductor switching element does not thermally break down when an excessive voltage is applied at the time of ON, and it is possible to prevent the semiconductor switching element from being thermally broken.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic circuit diagram of a semiconductor switch device 10 including a protection circuit 1 according to the present embodiment. However, since the configuration of the semiconductor switch device 10 is common to that described in the related art, the same reference numerals are given and the description is omitted.

The protection circuit 1 comprises a current detection resistor 2 connected between the source of the power MOSFET 14 and one of the output terminals 15b, and an npn-type transistor which is turned on when a voltage drop across the current detection resistor 2 exceeds a predetermined voltage. And the gate control transistor 3. Here, the current detection resistor 2 is made of a metal material (for example,
Al, Cu, W, Mo. Ti) and has a positive temperature coefficient. Note that this current detection resistor 2
Is the chip 1 together with the photovoltaic element 12 and the control circuit 13.
6b, or may be formed on the chip 16c together with the power MOSFET 14.

The operation of the protection circuit 1 according to this embodiment will be described. When an excessive voltage is applied to the drain of the power MOSFET 14 due to a load short circuit or the like, the voltage between both ends of the current detection resistor 2 rises and the gate control transistor 3 is turned on, and the gate-source voltage of the power MOSFET 14 Is reduced to a certain value to protect the power MOSFET 14. Moreover, since the current detection resistor 2 has a positive temperature coefficient, the resistance value of the current detection resistor 2 increases as the temperature rises due to the heat generated by the power MOSFET 14, and the voltage across the current detection resistor 2 increases. And the current detection resistor 2
Of the gate control transistor 3
Since the voltage applied between the base and the emitter of the power MOSFET 14 also increases, the gate voltage of the power MOSFET 14 decreases,
As shown in FIG. 2, the drain current Ids can be suppressed. As a result, since the power consumption of the power MOSFET 14 is reduced, the drain voltage tolerance (the maximum drain voltage at which the semiconductor switching element does not thermally break down when an excessive drain voltage is applied at the time of ON) Vds1 of the power MOSFET 14 is calculated. As shown in FIG. 2, the drain voltage tolerance Vds2 of the conventional example can be made higher to prevent thermal destruction of the power MOSFET 14 (here, FIG. 2 shows the current-voltage characteristics of the power MOSFET 14). ing).

The semiconductor switching device constituting the semiconductor switch device 10 has a power M of this embodiment.
The same effect is obtained even when another power device, for example, an IGBT is used instead of the OSFET 14.

[0012]

As described above, according to the present invention, a current detecting resistor connected between one end of a semiconductor switching element and one output terminal, and a gate of the semiconductor switching element in response to a voltage drop generated in the current detecting resistor. A gate control transistor for controlling the potential, and a resistor having a positive temperature coefficient is used as the current detection resistor. Therefore, when an excessive voltage is applied to the semiconductor switching element and the element temperature rises, the current detection resistor is used. Since the gate potential of the semiconductor switching element is reduced by the gate control transistor due to the increase in the voltage drop that occurs in the semiconductor switching element, the current flowing through the semiconductor switching element can be suppressed. On the other hand, the maximum voltage at which the semiconductor switching element does not thermally break can be increased,
There is an effect that thermal destruction of the semiconductor switching element can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram of a semiconductor switch circuit including an embodiment of the present invention.

FIG. 2 is a waveform chart showing current-voltage characteristics of a semiconductor switching element included in the semiconductor switch circuit of the above.

FIG. 3 is a schematic circuit diagram of a semiconductor switch circuit including a conventional example.

FIG. 4 is a waveform chart showing current-voltage characteristics of a semiconductor switching element included in the semiconductor switch circuit of the above.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Protection circuit 2 Current detection resistor 3 Gate control transistor 14 Power MOSFET

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 29/78 H03K 17/687 A H03F 1/52 H03K 17/687 (72) Inventor Masahiko Suzumura Kadoma, Osaka 1048 Matsushita Electric Works Co., Ltd., Kazumasa Tomii, Kazumasa Tomii 1048 Kadoma Kazuma, Kadoma City, Osaka Pref. Matsushita Electric Works Co., Ltd. F-term in the formula company F-term (reference) AA01 AA41 AA56 CA57 FA10 FP02 FP05 GP02 HA02 HA10 HA18 HA25 HA44 HA45 KA28 TA02

Claims (1)

[Claims] 1. A protection circuit for a semiconductor switch device wherein an output terminal is switched between a conductive state and a non-conductive state by a semiconductor switching element which is turned on and off according to a control input.
A current detection resistor connected between one end of the semiconductor switching element and one output terminal; and a gate control transistor for controlling a gate potential of the semiconductor switching element in accordance with a voltage drop generated in the current detection resistor, A protection circuit for a semiconductor switch device, wherein a resistor having a positive temperature coefficient is used as a detection resistor.