JP2001358568A - Semiconductor switching device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor switching device for controlling dv/dt to protect a switching element from breaking due to an avalanche current in an inductive load switching circuit. SOLUTION: A main switching element 1 and an auxiliary switching element 2 are provided on the semiconductor switching device, and a base current detecting terminal 6 capable of detecting the avalanche current flowing through a base is provided in the switching element 2. The difference between the detected current and a reference voltage 12 is fed back by a differential amplifier 11 through a sense resistor 7 from the detecting terminal, and the two pieces of dv/dt of the switching elements 1 and 2 are controlled not to turn a parasitic transistor on. The current density of the avalanche current by a surge voltage is supressed to protect the switching element due to the concentration of current, and thus, the semiconductor switching device with a stable output can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor switching device for detecting an avalanche current due to a surge current with a base current in an inductive load switching circuit and protecting a main switch element from overvoltage.

[0002]

2. Description of the Related Art In a conventional switching device, when a surge voltage generated from an inductive load is applied, the voltage is applied between the drain and the source of the semiconductor device, and the semiconductor device is avalanche, so that it is difficult to detect the surge voltage. Therefore, there is a fear that the semiconductor device is destroyed. Further, even when detecting the current of the main switching semiconductor device, detecting an avalanche state with the current flowing through an overcurrent to the main switching semiconductor device requires an excessive current to flow through the main switching element. There is a risk of destruction. There is also a method of detecting the voltage by providing a secondary winding.However, there is a concern that the power supply device may be enlarged, or that the surge voltage may be determined even when no surge voltage is applied, resulting in stabilization of the output voltage and poor efficiency. There is.

Japanese Patent Application Laid-Open No. 6-326318 discloses a semiconductor device provided with an insulating gate electrode control means for detecting an avalanche current, supplying a predetermined potential to the insulating gate electrode, and injecting carriers into the high-resistance semiconductor layer. JP 9
Japanese Patent No. 321302 discloses a semiconductor device having a main switch element and an electric field detection element for stable protection from overvoltage. These semiconductor devices have been proposed to reduce a surge voltage and are avalanche or equivalent. Detection in the method is performed at every turn-off, and becomes a new noise source. Further, since the gate control method is a passive method, it is difficult to perform optimal control.

That is, in the conventional gate control method, when a surge voltage is applied, the main switch element is shut off by detecting the surge voltage. Therefore, at the time of turn-off, the main switch element is sharply shut off, so that noise is generated. There is a problem that. In this way, the passive control method of forcibly shutting off the gate induces a new surge, which makes it difficult to absorb the surge voltage and prevent the generation of a new surge voltage.

FIG. 8 shows a conventional switching power supply circuit. A resistor for detecting an avalanche current is connected in series to the source 3 electrode of the main switch element 1, a voltage obtained here is input to the gate drive circuit 14, and a signal from the gate drive circuit 14 is transmitted to the gate 5 of the main switch element 1. To control the current of the main switch element 1.

However, there is a drawback that the current passing through the main switch element 1 is difficult to control in an avalanche state, and may be destroyed by the current flowing through the main switch element 1.
In particular, in a semiconductor device having a MOS structure, the avalanche characteristic of the inductive load is triggered by the operation of a parasitic transistor inherent in the MOS type field effect transistor.
Although it is an important design factor for high breakdown strength design together with the t-characteristic, it is difficult to obtain a semiconductor device that can sufficiently respond to this.

In general, when an inductance L is connected to a MOS semiconductor device as a load, a voltage exceeding the breakdown voltage of the semiconductor device is generated by the energy stored in the inductance L during the process of shifting the device to an off state by gate-off. Applied between sources. It is said that the avalanche causes a parasitic transistor to operate, leading to destruction of the element. Normally, as shown in FIG. 4, avalanche occurs at the P + main junction, hardly flows immediately below the n emitter, and the potential of the p base region does not rise.

However, as shown in FIG.
At the time of avalanche of 0, a high voltage is applied in a state where the drain current continues to flow and the depletion layer spreads greatly differently. Flowing through the p base region just below the emitter, the base potential can easily rise.

The hole current due to the avalanche flows as a base current immediately below the n-emitter to operate the parasitic transistor. The breakdown voltage is reduced by the operation of the parasitic transistor, and the rate of reduction in the breakdown voltage strongly depends on the base resistance and the magnitude of the hole current flowing into the base.

As shown in FIG. 6, by reducing dv / dt, the time required for the parasitic transistor to operate becomes longer, and the avalanche current due to the surge voltage does not flow to the p base region immediately below the emitter, but the surge energy increases. Consume.

As shown in FIG. 7, an avalanche occurs at the drain-source voltage VDS due to the inductive load, and a base current flows into the base regions of the cells 1 and 2. Cell 1
If the base resistance RBB1 is larger than the base resistance RBB2 of the cell 2, the parasitic transistor of the cell 1 operates first. Therefore, the withstand voltage of the cell 1 is lower than the withstand voltage of the cell 2, so that the current flowing around the cell 1 is drawn in, the withstand voltage is further reduced, and eventually the device is destroyed. In addition, one of the causes is a source contact defect, and concentration in one cell due to series resistance also causes destruction.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to reduce the hole current generated by avalanche, for example, by using a double diffusion type MOS field effect transistor. Is detected by the base current flowing through the base layer of
Dv / at the time of turn-off by the function of / dt controller
It is possible to provide a semiconductor switching device which controls so as to reduce dt and eliminates generation of a parasitic transistor due to avalanche and protects the main switch element from a surge voltage applied to the main switch element.

[0013]

SUMMARY OF THE INVENTION In order to achieve the above object, the invention according to the present invention uses two field effect transistors in a semiconductor device, wherein one of the field effect transistors is a double diffusion vertical MOS. The transistor is used as a main switch element, and the other field-effect transistor is a double-diffused vertical MOS transistor whose electrodes are connected to the source and the base, respectively, and each electrode is electrically insulated.
The transistor is used as an auxiliary switch element. A surge voltage is applied to the auxiliary switch element, thereby causing avalanche and a part of the avalanche current becomes a base current of the auxiliary switch element. Therefore, the base current is detected, and a voltage generated in the sense resistor is differentially detected. An amplifier outputs a difference output from a reference voltage to a dv / dt controller, and outputs an output of the dv / dt controller to gate electrodes of a main switch element and an auxiliary switch element to protect the avalanche current from a surge. .

The auxiliary switch element is provided with a terminal capable of detecting an avalanche current generated by the avalanche as a base current, and a sense resistor can be connected in series to the terminal. The sense resistor has a resistance that allows the base current flowing when an avalanche current is generated to be a voltage large enough to electrically detect it.The output voltage can be sent to the differential amplifier through a diode. it can. It is possible to reduce dv / dt by keeping the reference voltage constant, amplifying the difference from the reference voltage, outputting the difference to the dv / dt controller, and controlling the gate voltage so that dv / dt is reduced.

By reducing dv / dt, an avalanche current can flow to the base current of the main switch element and the auxiliary element without turning on the parasitic transistor, and the bias of the avalanche current in the switch due to the surge voltage can be reduced. It is possible to protect the main switch element and the auxiliary switch element from being destroyed by an avalanche current flowing. Further, only by changing dv / dt, the surge voltage is absorbed and no new surge voltage is generated.

By separately providing the source and base region electrodes of the double-diffused vertical MOS field-effect transistor of the auxiliary switch element separately and electrically, the avalanche current generated by avalanche can be detected as the base current. it can.

The main switch element is a double-diffused vertical MOS field effect transistor. Even if a surge voltage is generated at the time of turn-off, if the dv / dt of the gate is controlled, the turn-off is performed without turning on the parasitic transistor, and a new switch is turned on. No surge voltage is generated.

Since the two double-diffused vertical MOS field effect transistors, which are the main switch element and the auxiliary switch element, have a common drain electrode, the size can be reduced and the device is not enlarged. In addition, two double-diffused vertical MOS field effect transistors, which are a main switch element and an auxiliary switch element, can be formed on the same semiconductor substrate to minimize variations in characteristics between the main switch element and the auxiliary switch element. Can be.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a semiconductor switching device according to the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same members are given the same reference numerals,
Duplicate description will be omitted.

FIG. 1 shows an embodiment of the present invention, and FIG. 1 is a circuit diagram thereof. In this circuit diagram, the main switch element 1 and the auxiliary switch element 2 are arranged in parallel, and the auxiliary switch element 2 has a base current detection terminal 6 for detecting a base current 19.

FIG. 2 shows the structure of the main switch element 1 of the semiconductor switching device of the present invention, which is a double-diffusion vertical enhancement N-channel MOS transistor when the voltage (Vgs) between the gate and source 3 is 0V. Drain 4-
The source 3 is already off. Gate threshold is V
gs is in the positive region and when the threshold value is exceeded, the drain 4
-The source 3 is turned on. The main switch element 1
In the off state, a high breakdown voltage can be maintained between the drain 4 and the source 3.

Auxiliary switch element 2 of the semiconductor switching device shown in FIG. 3 is a double-diffusion vertical enhancement N-channel MOS transistor provided with electrodes electrically separated from source 3 and base region, respectively. . The base current detection terminal 6 is grounded via a sense resistor 7. Therefore, the voltage between the gate 5 and the source 3 (V
When gs) is 0 V, it is off. When the voltage between the gate 5 and the source 3 exceeds the threshold and rises, the state between the drain 4 and the source 3 is turned on. Auxiliary switch element 2
Is the same drain or source 3 as the main switch element 1 or less.
Indicates the withstand voltage.

When the main switch element 1 and the auxiliary switch element 2 rapidly transition from the on state to the off state, FIG.
, The drain voltage increases. When the drain voltage exceeds the withstand voltage of the auxiliary switch element 2, an avalanche current flows, and the base current 19 of the auxiliary switch element 2 also increases. The base current 19 is taken out by the sense resistor 7, and excess current is bypassed by the Zener diode 8.

The voltage obtained by the sense resistor 7 is compared with a reference voltage 12. If the voltage 6 generated by the sense resistor 7 is large, the voltage is output from the error amplifier 11 and fed back to the dv / dt controller 13. The dv / dt controller 13 is dv / dt
dt, the turn-off speed of the main switch element 1 and the auxiliary switch element 2 is reduced, and the parasitic transistor 1
5. It is possible to consume energy without turning on 5.

Accordingly, it is possible to suppress the generation of the avalanche current 17 due to the generation of the drain voltage exceeding the withstand voltage of both switch elements, which may occur when the main switch element 1 and the auxiliary switch element 2 are turned off.

Further, as in the invention according to the fourth aspect, the sense resistor 7 for detecting the base current 18 of the auxiliary switch element 2 can electrically detect the base current 19 flowing when the avalanche current 17 is generated. Since it has a sufficiently large resistance value that can be set to a large voltage, the base current 19 can be easily detected, and the voltage generated by the current flowing therethrough is used as the differential amplifier 11.
, And the excess voltage can be bypassed by the Zener diode 8.

An error amplifier according to a fifth aspect detects a difference between a voltage detected by the sense resistor and a reference voltage, and outputs the difference to a dv / dt control circuit. dv
/ Dt control circuit 13 is a gate drive circuit 14
Dv / dt of the signal obtained from the above is reduced when the avalanche state of the auxiliary switch element 2 is detected by the base current 19, and is controlled to be as large as possible when the avalanche state is not detected.

According to a sixth aspect of the present invention, when the semiconductor switching device is formed on one substrate, the main switch element 1, the auxiliary switch element 2, the sense resistor 7, and the Zener diode can be miniaturized and controlled stably. 8 can be provided.

According to the seventh aspect of the present invention, connecting the main switch element 1 and the auxiliary switch element 2 in parallel makes the on-resistance of the main switch element 1 as small as possible. Can be optimally designed for each purpose so that can be detected with high sensitivity.

According to the eighth aspect of the present invention, the main switch element 1 and the auxiliary switch element 2 are formed on the same semiconductor substrate, so that the switching between the main switch element 1 and the auxiliary switch element 2 such as variation in the switching operation can be achieved. Characteristics can be aligned.

According to the semiconductor switching device, the MOS
An avalanche current 17 is detected by a sense resistor 7 from a terminal for detecting a base current 19 of the auxiliary switch element 2, and a main switch element 1 and an auxiliary switch element 2 are arranged in parallel. And dv / d is fed back to the gate 5 of the auxiliary switch element 2.
The switching circuit that controls t can provide a semiconductor switching device that can prevent the main switch element 1 and the auxiliary switch element 2 from being destroyed by a surge current.

[0031]

[Brief description of the drawings]

FIG. 1 is an example of a switching circuit showing an embodiment of the present invention.

FIG. 2 is an embodiment showing a structure of a main switching element of the present invention.

FIG. 3 is an embodiment showing a structure of an auxiliary switch element of the present invention.

FIG. 4 is a diagram illustrating an avalanche generation region.

FIG. 5 is a diagram illustrating a region where an avalanche base current flows.

FIG. 6 shows dv / dt until a parasitic transistor is turned on.
It is a figure explaining change of.

FIG. 7 is a diagram for explaining that a current bias occurs due to activation of a parasitic transistor due to an avalanche current.

FIG. 8 is a diagram showing a conventional switching circuit.

[Explanation of symbols]

 1. Main switch element 2. Auxiliary switch element 3. Source 4. Drain 5. Gate 6. Base current detection terminal 7. Sense resistor 8. Zener diode 9. Diode 10. Capacitor 11. Error amplifier 12. Reference voltage 13. Gate dv / dt controller 14. Gate drive circuit 15. Parasitic transistor 16. Base resistance 17. Avalanche current 18. Hole current 19. Base current 20. Inductance

Claims (8)

[Claims] An inductive load switching circuit using a semiconductor device having two field-effect transistors,
An avalanche current is generated by an overvoltage applied to one of the field-effect transistors, and when the avalanche current occurs, a base resistor that detects a base current flowing to the base of the semiconductor device is detected by a sense resistor. An avalanche generation state is detected, and the dv / dt of the two field effect transistor gates is detected by an error amplifier.
Semiconductor switching device having means for controlling 2. The semiconductor switching device according to claim 1, wherein one field-effect transistor of the semiconductor device is an auxiliary switching element, and is a MOS type semiconductor element and has a base current in addition to the source, drain and gate terminals. A semiconductor switching device comprising an auxiliary switch element having a terminal capable of detecting a voltage. 3. The semiconductor switching device according to claim 1, wherein one field effect transistor of the semiconductor device is a main switch element and is a MOS type semiconductor element. 4. A semiconductor switching device according to claim 1, wherein the sense resistor has a sufficient size to make it possible to electrically detect a base current flowing when an avalanche current is generated. A semiconductor switching device having a value, one terminal being connected to an error amplifier through a base current detection terminal of a main switch element and a diode, and the other being grounded. 5. The semiconductor switching device according to claim 1, wherein the voltage detected by the sense resistor is compared with a reference voltage by an error amplifier. A semiconductor switching device comprising a gate dv / dt controller for controlling voltage dv / dt to be small. 6. The semiconductor switching device according to claim 1, wherein the main switch element, the auxiliary switch element, the sense resistor, and the Zener diode are formed on one substrate. 7. The semiconductor switching device according to claim 1, wherein the two field effect transistors are a main switch element and an auxiliary switch element, and the field effect transistors are connected in parallel. Switching device. 8. The semiconductor switching device according to claim 1, wherein two field effect transistors are formed on the same semiconductor substrate.