JPH05268024A - Switching circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To achieve high-speed switching and high output withstand voltage in switching circuits for semiconductor integrated circuits. A collector of the first transistor 11 is connected to a first terminal 61 serving as an output terminal, a collector of the second transistor 12 is connected to an emitter of the first transistor 11, and an emitter thereof serves as a ground terminal. 2 terminal 62
And a third transistor 13 controls the base of the second transistor 12 to turn on / off the second transistor 12. Then, the first transistor 11 and the third transistor 13 are turned on / off directly or indirectly by an on / off input signal at the third terminal 63 connected to the signal line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching circuit, and more particularly to a switching circuit which can obtain a high breakdown voltage, can be easily integrated, and can perform high-speed switching.

[0002]

2. Description of the Related Art Conventionally, the first and second terminals are connected to an external circuit including an electric power source, in which an open circuit is formed,
Whether there is continuity between the first and second terminals is determined by the third terminal (input terminal)
A switching circuit is often used in which an electric current is supplied to an external circuit or not supplied by switching it by an on / off signal input to the external circuit. An example of this switching circuit is shown in FIG. This circuit includes a first terminal 91 and a second terminal
It is used to connect the power supply 76 and the circuit 75 to the terminal 92 via a ground, and is turned on / off by an on / off input signal input to the base of the switching transistor 71. The control circuit 81 controls the base current of the transistor 71 by the ON / OFF signal input to the third terminal 93 serving as an input terminal to turn on / off the transistor 71. In FIG. 6, when the potential of the first terminal 91 exceeds the collector-emitter breakdown voltage or the collector-base breakdown voltage of the transistor 71 when the output transistor 71 is off, breakdown occurs. FIG. 7 is a specific example of the circuit shown in FIG. In FIG. 7, the control circuit 81 is replaced with a transistor 73 and a constant current source 85. Incidentally, 94 is a _Vcc power supply terminal. In the specific example shown in FIG. 7, the breakdown voltage of the first terminal 91 is almost the collector-base breakdown voltage BV _CBO .

Next, in order to improve the output breakdown voltage, a circuit as shown in the block diagram of FIG. 8 can be considered. Eggplant,
The switching element 83 is provided at the base of the output transistor 71.
While the switching element 84 is connected to the emitter of the output transistor 71. Then, the control circuit 82
Is for controlling the switching elements 83 and 84. Thus, when the output is off, the output breakdown voltage is improved by opening the switching elements 83 and 84 and disconnecting the base terminal and the emitter terminal of the transistor 71. FIG. 9 shows a specific example of the circuit shown in FIG. 8 (see Japanese Patent Laid-Open No. 60-182216). In FIG. 9, the switching element 83 is replaced with a diode 86,
On the other hand, the switching element 84 is replaced by the transistor 72. The third terminal 93 is an input terminal, and 87 and 88 are resistors that control the base currents of the transistors 71 and 72, respectively.

[0004]

However, in the circuit of FIG. 9, there is a parasitic capacitance between the base and the emitter of each of the transistors 71 and 72 and between the collector and the base.
Each of the transistors 71 and 72 causes a delay in on / off switching by the time for charging or discharging these parasitic capacitances. In particular, when the transistors 71 and 72 are driven to saturate, the switching from on to off is slow due to the base accumulated charge. First, the case of the transistor 71 is as follows. At the time of switching from on to off, the charge accumulated in the base of the transistor 71 is in the opposite direction to the diode 86, so that the diode 8
It cannot be discharged through a forward resistance of 6. Therefore, the base accumulated charge is only discharged by the parasitic capacitance of the diode 86 and the self-discharge of the transistor 71, so that the switching from on to off is delayed. next,
In the case of the transistor 72, it becomes as follows. The resistor 88 connected to the base of the transistor 72 has a relatively high resistance value because it causes a voltage drop of the forward voltage V _F or more of the diode 86. Therefore, the parasitic capacitance of the base of the transistor 72 is charged and discharged through the resistor 88, and the on / off switching speed of the transistor 72 is also slowed down. Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a switching circuit having a high breakdown voltage at an output terminal and an improved on / off switching speed.

[0005]

Therefore, in order to solve the above-mentioned problems, the present invention provides first and second circuits connected to an external circuit.
A switching circuit that has a terminal and a third terminal connected to a signal line, and switches the presence / absence of conduction between the first and second terminals according to an on / off signal input to the third terminal,
A signal in which at least two or more transistors are connected in series between the first and second terminals, and the base of at least one or more of the two or more transistors is on / off controlled by the on / off signal. The switching circuit is characterized in that the switching circuit is connected to a transistor for turning on / off the one or more transistors.

[0006]

According to the switching circuit having the above structure,
Since at least two or more transistors are connected in series between the second terminals, the breakdown voltage between the first and second terminals is improved. The base of at least one of the two or more transistors connected in series is connected to a signal transistor that is turned on / off by an on / off input signal, and the signal transistor is turned on / off. As a result, the one or more transistors are turned on / off, so that the switching time of the one or more transistors from on to off is short, and therefore the switching time between the first and second terminals can be shortened. If even one of the transistors connected in series is turned off,
The first and second terminals are turned off.

[0007]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a circuit diagram showing a first embodiment of the present invention. In FIG. 1, the output transistor 11 is
The base is connected to the cathode of the diode 21, and the collector is connected to the first terminal 61 serving as an output terminal. The collector of the transistor 12 is the transistor 1
The second terminal 6 whose emitter serves as a ground terminal
2 are connected to each. In addition, transistor 1
3, the base is connected to the third terminal 63 via the resistor 41, the collector is connected to the base of the transistor 12, and the emitter is connected to the second terminal 62. Next, the constant current source 31
Between the V _cc power supply terminal 64 and the collector of the transistor 13, the constant current source 32 is connected to the V _cc power supply terminal 64 and the diode 2
And one anode. Further, the base of the transistor 14 is connected to the third resistor via the resistor 42.
The terminal 63, the collector is the anode of the diode 21,
The emitters are connected to the second terminals 62, respectively. The third terminal 63 is connected to the signal line and serves as an input terminal.

With the above structure, the first terminal 61
Since the base of the transistor 12 of the transistors 11 and 12 connected in series between the second terminals 62 is connected to the signal transistor 13, when the on / off input signal is input to the transistor 13, the transistor 12 Turns on and off, resulting in the first terminal 61.
The second terminal 62 is turned on and off.

That is, when the transistor 13 is on, the current of the constant current source 31 flows through the collector / emitter of the transistor 13 and does not flow into the base of the transistor 12. At that time, the base of the transistor 12 is connected to the second terminal 62 via the collector / emitter of the transistor 13. As a result, the transistor 12 is turned off. On the other hand, when the transistor 13 is off, the current of the constant current source 31 becomes the base current of the transistor 12,
The transistor 12 is turned on. Therefore, since the transistor 13 directly turns on / off the transistor 12 as an off-buffer, the switching delay due to the electric charge accumulated in the base of the transistor and the resistance connected to the base as in the conventional example is eliminated, and the switching speed is improved. be able to. Therefore, the switching speed between the first terminal 61 and the second terminal 62 can be improved. When the transistor 14 is on, the constant current source 32
Current flows to the collector / emitter of the transistor 14, and the diode 21 is turned off. Conversely, transistor 1
4 is off, the current of the constant current source 32 is the diode 2
1 and the base of transistor 11 and diode 2
1 and the transistor 11 are turned on.

As described above, when a positive voltage larger than the base-emitter voltage of the transistors 13 and 14 is applied to the third terminal 63, the transistors 13 and 14 are turned on and the diode 21 and the transistors 11 and 12 are turned off. Become. On the contrary, when the third terminal 63 is grounded, the transistors 13 and 14 are turned off, and the diode 21 and the transistors 11 and 12 are turned on. In this way, the third terminal 6
When a positive pulse voltage larger than the base-emitter voltage of the transistors 13 and 14 is applied to the transistor 3, the transistors 11 and 12 perform high speed and high breakdown voltage switching operation.

Therefore, the diode 21 and the transistor 12, which are respectively connected to the base and the emitter of the output transistor 11, operate as a switching element. Therefore, when the output is off, the diode 21 and the transistor 12 are turned off, and the base terminal and the emitter terminal of the transistor 11 are separated, so that the output breakdown voltage is improved. When the output is off, as described above, the transistor 1
Since 2 is directly pulled down by the transistor 13, the collector breakdown voltage of the transistor 12 is almost BV _CBO.
Becomes At this time, the collector breakdown voltage of the transistor 11 is BV _CEO . Therefore, the breakdown voltage of the output terminal 62 when the output is off is BV _CEO + BV _CBO , which is higher than that of the conventional circuit shown in FIG. Furthermore, if the number of transistors 12 is two or more, the breakdown voltage can be further increased. The switching element is not limited to the diode 21 and the transistor 12. As the transistor 12, a source-grounded FE is used.
It is also possible to use T.

FIG. 2 shows a second embodiment of the present invention. In FIG. 2, the constant current source 33 and the constant current source 34 correspond to the constant current source 31 and the constant current source 32 of FIG. 1, respectively,
The transistor 15 has a base connected to the third terminal 63, an emitter connected to the base of the transistor 13, and a collector connected to the constant current source 34. A resistor 43 is connected between the base and emitter of the transistor 13. The other structure is the same as that of the first embodiment. With the above configuration, the transistor 15 and the transistor 13 perform two-stage current amplification, so that a switching circuit having a high input impedance at the third terminal 63 can be formed.
Then, when an on / off input signal is input to the third terminal 63, the transistors 15 and 13 are turned on and off, and the transistors 11 and 12 are turned on and off as in the first embodiment.
Turn off.

FIG. 3 shows a third embodiment of the present invention. In FIG. 3, instead of the diode 21 of FIG. 2, a transistor 25 having an emitter / collector replaced.
Transistor 25 has a base connected to the collector of transistor 15 and an emitter connected to V _CC via resistor 44.
The collector is connected to the power supply terminal 64 and the base of the transistor 11, respectively. The constant current sources 35 and 36 correspond to the constant current sources 33 and 34 of the second embodiment described above, respectively. Further, the resistor 45 is the resistor 43 of the second embodiment described above.
Equivalent to. The other structure is the same as that of the second embodiment described above. Normally, the breakdown voltage between the emitter and base of the transistor is low, and the breakdown voltage between the collector and base of the transistor is high, so the transistor 2
By connecting 5 in this way, the required breakdown voltage can be obtained even if the diode 21 is omitted. Further, in this case, the transistor 25 has the current amplification factor h _FE
However, since it works as a transistor, the constant current source 36 can be made smaller. Therefore, the current consumption when the output is off can be reduced. When an on / off input signal is input to the third terminal 63, the transistors 15 and 13 are turned on and off and the transistors 11 and 12 are turned on and off, as in the second embodiment. ..

FIG. 4 shows a fourth embodiment. Figure 4
In, only the constant current source 37 is used as the constant current source. Therefore, in the transistor 16, the base is connected to the constant current source 37 via the resistor 48, the collector is connected to the V _cc power supply terminal 64 via the resistor 46, and the emitter is connected to the anode of the diode 21. The base of the transistor 17 is connected to the constant current source 37 via the resistor 49, and the collector is V connected via the resistor 47.
_It is connected to the _cc power supply terminal 64 and the emitter is the diode 22.
Is connected to the base of the transistor 12 via.
Further, the transistor 18 has a base connected to the third terminal 63, a collector connected to the constant current source 37, and an emitter connected to the base of the transistor 13. The resistor 50 is connected between the base and emitter of the transistor 13. The other structure is the same as that of the second embodiment described above. With the above configuration, when the transistor 18 and the transistor 13 are off, the current of the constant current source 37 is shunted to the base of the transistor 16 via the resistor 48 and to the base of the transistor 17 via the resistor 49. .. Therefore, the transistor 06 turns on and the diode 21 turns on, while the transistor 17 turns on, the diode 22 turns on, the transistor 12 turns on, and the transistor 11 turns on. Conversely, when the transistor 18 is on, the transistor 13 is on, the transistor 12 is off, the transistor 16 is off, the diode 21 is off, and the transistor 11 is off. Therefore, when an on / off signal is input to the third terminal 63, the transistors 11 and 12 are turned on / off as in the second embodiment. Then, as the constant current source, only the constant current source 37 is the transistor 1
Since the base currents of the transistors 11 and 12 flow via 6 and 17, the value of the constant current source 37 can be reduced, so that the current consumption when the output is off can be further reduced.

FIG. 5 shows a fifth embodiment. Figure 5
In, the transistor 26 and the transistor 27 are
Similar to the transistor 25, the collector and the emitter are replaced. Therefore, the diode 21 and the diode 22 in FIG. 4 are unnecessary. 38
Are constant current sources and 51 to 56 are resistors. With the above configuration, similarly to the above-described fourth embodiment, when an on / off signal is input to the third terminal 63, the transistors 11 and 12 are turned on / off to reduce the current consumption when the output is off. be able to.

In each of the above embodiments, the transistor may be replaced by a diode, or the resistor may be omitted. The constant current source may be replaced with a resistor. Further, although the NPN open collector is described as an example, each may be Darlington connection, or may be replaced with a PNP transistor with the polarity reversed. Furthermore, a part or all of the junction type FET,
It may be an active element such as a MOSFET. In addition, if the transistor 12 has two or more stages as described above, the breakdown voltage can be further increased.

[0017]

As described in detail above, according to the switching circuit of the present invention, the breakdown voltage of the output terminal can be increased by high-speed switching. For this reason, in integrated circuits, the power supply and others have been regulated to a constant voltage, and low withstand voltage is sufficient. The breakdown voltage of the output terminal can be increased without using it. Therefore, the IC chip size can be reduced or the cost can be reduced.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a fourth embodiment of the present invention.

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

FIG. 6 is a circuit diagram showing a conventional example.

FIG. 7 is a specific example of the circuit shown in FIG.

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

FIG. 9 is a specific example of the circuit shown in FIG.

[Explanation of symbols]

 11 Transistor 12 Transistor 13 Transistor 61 First Terminal 62 Second Terminal 63 Third Terminal

Claims (1)

[Claims] 1. A first and a second terminal connected to an external circuit and a third terminal connected to a signal line, wherein the first terminal is responsive to an on / off signal input to the third terminal. A switching circuit for switching the presence / absence of conduction between the second terminals, the first circuit
At least two or more transistors are connected in series between the second terminals, and the base of at least one or more of the two or more transistors is a signal transistor whose on / off is controlled by the on / off signal. A switching circuit which is connected to turn on / off the one or more transistors.