JPH077399A - Switching circuit - Google Patents

Abstract

PURPOSE:To generate a large voltage against such a large current as a short circuit current, and to maintain a reverse bias action by providing with a means which does not output an ON-signal to a switch device, when a switching means is ON. CONSTITUTION:When a switch 6 is turned on, and a large power source short circuited current flows through a transistor 3 and the switch 6, a large voltage drop is generated in a current limiting means 4, and a large base reverse bias voltage is impressed to its emitter junction. Also, even if a load current flows between terminals 12, 13 during an ON-period of the switch 6, its current is smaller than the power source short circuited current, and only a small voltage drop is generated in the means 4, therefore, an energy loss by the means 4 is small. In such a way, as keeping a large reverse bias voltage maintaining, the energy loss can be decreased.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a switching circuit having a function like a changeover switch such as a three-terminal switch and an arm pair. With the present invention, for example, a closed circuit including a certain DC voltage source and a certain load can be formed, or a closed circuit including only that load can be formed. Therefore, the present invention provides a drive circuit for switching means, a power conversion circuit, a logic circuit, or a drive circuit for a capacitive load (for example, a display circuit for a gas discharge display panel or an electroluminescence display panel, a drive for a piezoelectric element). Circuit etc.) etc.

[0002]

[Background Technology] FIGS. 2 to 4 show, as a conventional technique, a switching circuit having a power supply short-circuit avoidance function and a 3-terminal switch function to some extent. The series circuit of the plurality of diodes 7 constitutes a constant voltage means. The switch 6 may be any type of switch including a semiconductor switch. still,
Instead of the gate turn-off type thyristor 8 in the circuit of FIG. 3, an equivalent circuit of a thyristor composed of both PNP and NPN transistors or a similar equivalent circuit can be used. In addition, the inventor has found that the circuit of FIG.
I showed an example of using FET, but instead of normal
Any off, voltage driven switch device can be used. For example, ordinary FET, IGBT (I
Insulated Gate Bipolar Tran
system), SIT (static induction transistor), S
I-thyristor, Bi-MOS composite device.

In any switching circuit, the power supply short-circuit current flowing when the switch 6 is turned on causes the semiconductor switch device (transistor 3 or 12,
Alternatively, the thyristor 9) is reverse biased. as a result,
The greater the short circuit current, the stronger the reverse bias effect and the faster the turn off of each switch device. Therefore, the short circuit ends in an instant, and the damage like a normal power supply short circuit is reduced. For that reason, each switching circuit has some self-shorting avoidance function. However, in order to strengthen the reverse bias action, it is necessary to increase the voltage drop due to the series circuit of the plurality of diodes 7, that is, the voltage drop due to the constant voltage means to some extent.

However, in such a switching circuit, there is a problem that the total on-voltage of the series circuit of the plurality of diodes 7 and the switch 6 also increases and the loss increases.

Therefore, an object of the present invention is to provide a switching circuit which can maintain its reverse bias action without increasing such loss.

[0006]

[Disclosure of the invention] That is, the present invention is
There is a switch device that is an off type and has a self-turn-off function, and its control terminal and main terminal are control terminals ct,
When the main terminals mta and mtb are used and the control terminal ct and the main terminal mta form a pair for inputting the drive signal thereof, the current limiting means for limiting the maximum value of the current flowing through itself is the main terminal mta. The switch device and the current limiting means are connected in series so that the switch device, the current limiting means and the switching means are connected in series between both power supply terminals of the DC voltage source, The switching circuit is provided with an ON signal output unit that connects the current limiting unit between the terminal mta and the control terminal ct and does not output an ON signal to the switch device when the switching unit is ON.

As a result, the current limiting means generates a large voltage for a large current such as a power supply short-circuit current, so that a sufficient reverse bias voltage is supplied to the switch device when the switching means is turned on. To be done. On the other hand, since the current limiting means generates only a small voltage with respect to the normal load current, the loss due to the switching means and the current limiting means can be small. Thus, the present invention has the effect that its reverse biasing action can be maintained without increasing such losses.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In order to describe the present invention in more detail, it will be described below with reference to the accompanying drawings. In the embodiment of FIG. 1, the DC power supply 1 is the aforementioned DC voltage source, the transistor 3 is the aforementioned switching device, the current limiting means 4 is the aforementioned current limiting means, the switch 6 is the aforementioned switching means, and the resistance is 2 corresponds to the ON signal output means described above. The switch 6 may be any type of switch including a semiconductor switch.
Examples of the current limiting means include current limiting means shown in FIGS.

The operation of the switching circuit shown in FIG. 1 will be briefly described. When switch 6 turns on and a large power supply short-circuit current flows through transistor 3 and switch 6, a large voltage drop occurs in current limiting means 4, so a large base reverse bias voltage is applied to its emitter junction.
Of course, be careful that the reverse bias voltage does not exceed the reverse withstand voltage between the base and emitter. On the other hand, switch 6
Even when a load current flows between the terminals t2 and t3 during the ON period of, the current is smaller than the power supply short-circuit current described above, so that only a small voltage drop occurs in the current limiting means 4, and the energy of the current limiting means 4 is reduced. The loss is small. In this way, such energy loss can be reduced while maintaining a large reverse bias voltage. It should be noted that the two Zener diodes indicated by the dotted lines correspond to the voltage limiting means in the fifth aspect, and these should be provided to protect the emitter junction of the transistor 2 from reverse overvoltage.

The switching circuit of FIG. 5 is an embodiment using a gate turn-off type thyristor 9. Instead of the thyristor 9, an equivalent circuit of a thyristor composed of PNP or NPN type transistors or a similar equivalent circuit can be used.

The switching circuit shown in FIG. 6 is a MOS FET.
It is an example using. Even if a bipolar transistor is used instead of the transistor 12, the gate turn-off
You can use a thyristor or any normally-off, self-turn-off switch device.

Most of the switching circuits of FIG. 7 are similar to those of FIG.
In the circuit of, the switch 6 is connected to the transistor 3
This is a switching circuit in which the base side is changed to the collector side. A plurality of diodes 14 protect the emitter junction of the transistor 3 from reverse overvoltage.

8 to 13 show examples of the current limiting means.
The means of FIG. 8 is a constant current means using a normally-on type FET, and the means of FIG. 9 is a normally-on type MOS.FE.
It is a constant current means using T and a resistor, both of which are well known.

In the means of FIG. 10, when the current in the resistor 16 increases, the resistor 17 pulls the base of the transistor 15 in the reverse bias direction. In the means of FIG. 11, the transistor 18 is used to increase the pulling force.

In the means of FIG. 12, the equivalent circuit of the thyristor formed by the transistors 15 and 19 is used instead of the transistor 15 in the means of FIG.

In the means of FIG. 13, the current limiting transistor 20 and the like are connected not only to the transistor 15 side but also to the transistor 19 side.

The switching circuit of FIG. 14 is almost the same as the switching circuit of FIG. 5, except that the equivalent circuit is used instead of the thyristor 9 and the connection position of the switch 6 is changed from the gate side to the anode side.

In the switching circuit of FIG. 15, the connection position of the switch 6 is generally the transistor 12 in the circuit of FIG.
This is a switching circuit in which the gate side is changed to the drain side. 21 is a load.

[0019]

[Prior art] JP-A-47-31568,
Japanese Utility Model Publication No. 47-14052 and Japanese Patent Application Laid-Open No. 61-142.
No. 819.

No. 53-59358, KAIKAI,
JP-A-53-123060-2 and JP-A-60-208
No. 119.

JP-A-55-3259,
JP-A-55-136727, JP-A-58-12432
No. 4, JP-A-58-21920, and JP-A-SHO-5
No. 8-36020.

[0022]

[Kanren patent] (Japanese Patent Application No. 63-43334),
Japanese Patent Application No. 1-199326.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a conventional switching circuit.

FIG. 3 is a circuit diagram showing a conventional switching circuit.

FIG. 4 is a circuit diagram showing a conventional switching circuit.

FIG. 5 is a circuit diagram showing an embodiment of the present invention.

FIG. 6 is a circuit diagram showing an embodiment of the present invention.

FIG. 7 is a circuit diagram showing an embodiment of the present invention.

FIG. 8 is a circuit diagram showing an example of a current limiting means used in the present invention.

FIG. 9 is a circuit diagram showing an example of current limiting means used in the present invention.

FIG. 10 is a circuit diagram showing an example of current limiting means used in the present invention.

FIG. 11 is a circuit diagram showing an example of a current limiting means used in the present invention.

FIG. 12 is a circuit diagram showing an example of current limiting means used in the present invention.

FIG. 13 is a circuit diagram showing an example of current limiting means used in the present invention.

FIG. 14 is a circuit diagram showing an embodiment of the present invention.

FIG. 15 is a circuit diagram showing an embodiment of the present invention.

[Explanation of code]

 4 current limiting means 21 load t1 to t3 terminals

Claims (7)

[Claims] 1. A normally-off type switch device having a self-turn-off function, wherein a control terminal and a main terminal thereof are a control terminal ct and main terminals mta and mtb, and the drive signal is inputted to the switch device. When the control terminal ct and the main terminal mta form a pair, the switch device and the current limiting device are arranged so that current limiting means for limiting the maximum value of the current flowing through the control terminal ct comes to the main terminal mta side. Means connected in series, said switch device between both power supply terminals of the DC voltage source,
The current limiting unit and the switching unit are connected in series, the current limiting unit is connected between the main terminal mta and the control terminal ct, and an ON signal is not output to the switch device when the switching unit is ON. A switching circuit comprising an ON signal output means. 2. The switching means is connected to the control terminal c.
The switching circuit according to claim 1, wherein the switching circuit is connected to the t side. 3. The switching means is connected to the main terminal mt.
The switching circuit according to claim 1, wherein the switching circuit is connected to the b side. 4. The switching circuit according to claim 1, 2 or 3, wherein a constant current means is used as the current limiting means. 5. The voltage limiting means for suppressing the reverse bias voltage applied between the control terminal ct and the main terminal mta to be equal to or less than the reverse withstand voltage thereof is provided.
Alternatively, the switching circuit according to item 4. 6. The switching circuit according to claim 5, wherein a constant voltage means is used as the voltage limiting means. 7. The switching circuit according to claim 5, wherein surge voltage absorbing means is used as the voltage limiting means.