JPS62120120A - Signal switching device - Google Patents

Abstract

PURPOSE:To save number of components by combining an NPN transistor (TR) and a PNP TR and using two TRs so as to switch two signals selectively. CONSTITUTION:When a switch 20 is turned on, a base current of a PNP TR 13 flows from ground to a negative power supply 19 via the emitter-base of the TR 13 and a resistor 7. As a result, the TR 13 is turned on. Thus, the base potential of the TRs 12, 13 is -VBE and the potential is a reverse bias to the TR 12, the TR 12 is turned off. Thus, a signal A passes through, a signal B is shut and the signal A is outputted to an output terminal 17. When the switch 20 is turned off, the signal B is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a signal switching circuit that selectively switches between two signals.

BACKGROUND OF THE INVENTION In recent years, signal switching circuits have been used in most audio products, and many types are known, including those using mechanical switches and those using semiconductor switches.

An example of a conventional signal switching circuit will be described below with reference to the drawings.

FIG. 2 shows a circuit diagram of a conventional signal switching circuit. In FIG. 2, 1 and 2 are input terminals for signals A and B, which are connected to transistors 12.1 through resistors 3 and 5, respectively.
It is connected to 14 collectors. 4 and 6 are resistors connected to the collectors of the transistors 12 and 14, respectively.

Reference numeral 17 is an output terminal to which the resistors 4 and 6 mentioned above are connected. The emitter of the transistor 12 is connected to ground, and the base thereof is connected to a positive power source 18 via resistors 9 and 8. The emitter of the transistor 14 is connected to ground, and the base is connected to a positive power supply 18 via a resistor 1o. The base of the transistor 14 is simultaneously connected to the collector of the transistor 15, the emitter of the transistor 16 is connected to ground, and the base is connected via the resistor 11 to the connection point of the resistors 9 and 8 and one terminal of the switch 20. ing. The other terminal of the switch 20 is connected to ground.

The operation of the signal switching circuit configured as described above will be explained below.

First, consider the case where the switch 20 is turned on. In this case, since the base currents of the transistors 12 and 15 do not flow, the transistors 12 and 16 are turned off. Since the transistor 16 is in the OFF state, a base current flows through the transistor 14 through the resistor 10.
Transistor 14 is turned on. Therefore, since the transistor 12 is OFF and the transistor 14 is ON, the signal A passes through, the signal B is cut off, and the signal A is output to the output terminal 17. Next, consider the case where the switch 20 is OFF. In this case, the transistor 12 has a resistor 8
, 9, and the base current flows to the transistor 15 via the resistors 8 and 11. As a result, the transistors 12.15 are turned on. Since the transistor 16 is in the ON state, no base current flows through the transistor 14, and the transistor 14 is turned OFF. Therefore, transistor 12 is turned on, and transistor 12 is turned on.
4 is turned OFF, the signal A is not cut off, the signal B passes through, and the signal B is outputted to the output terminal 1T.

In other words, when the switch 20 is ON, the signal A is output,
When it is OFF, signal B is output.

Problems to be Solved by the Invention However, the above configuration requires three NPN transistors, which leads to a problem of cost amplifiers.

In view of the above problems, the present invention provides an NPN transistor and a PN transistor.
Combining P transistors, 2F transistors
The present invention provides a signal switching circuit that can selectively switch between two signals.

Means for Solving the Problems In order to solve the above problems, the signal switching circuit of the present invention has the following features:
It has an NPN transistor and a PNP transistor whose collectors or emitters are both grounded. The feature is that the resistor inserted between the two power supplies is connected to the connection point of the switch.

Effects According to the present invention, with the above-described configuration, when one transistor is ON, the other transistor is always reverse biased and turned OFF, so that two signals can be selectively switched using two transistors. becomes.

Embodiments Hereinafter, signal switching circuits according to embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a circuit diagram of a signal switching circuit in one embodiment of the present invention. In Figure 1, 1 and 2 are signals A
, H, which are connected to the collectors of transistors 12 and 13 via resistors 3 and 6, respectively. 4
, 6 are resistors, and the transistors 12.1 and 12.1 are resistors, respectively.
3 collector. 17 is an output terminal to which the resistors 4 and 6 are connected. The emitters of the transistors 12 and 13 are connected to each other and grounded, and the bases of the transistors 12 and 13 are also connected to the positive power source 18 through the resistor hole 8. A switch 20 is connected between the connection point of the resistors 7 and 8 and the negative power supply 19.

The operation of the signal switching circuit configured as described above will be explained below with reference to FIG. 1.

First, consider the case where switch 2Q is turned on. In this case, the PNP is connected from the ground to the negative power supply 19 via the emitter base of the PNP transistor 13 and the resistor 7.
The base current of transistor 13 flows. As a result, the PNP transistor 13 is turned on. Therefore, the base potential of the transistors 12 and 13 is 1 BE (approximately -o, 5 sV in the case of silicon transistors), and the NP
Since the N transistor 12 is reverse biased,
The NPN transistor 12 is turned off. Therefore,
NPN transistor 12 is off, PNP transistor 1
3 is ON, signal A passes through, signal B is cut off, and signal A is output to output terminal 1.

Next, consider the case where the switch 20 is OFF. in this case,
A base current flows through the transistor 12 from the positive power supply 18 via the resistors 8 and 7. As a result, the above N P N l
- The transistor 12 is turned on. Therefore, the base potential of transistors 12 and 13 becomes +vBE, and since the PNP transistor 13 is reverse biased, the above-mentioned P
NP transistor 13 is turned off. Therefore, N.P.
Since the N transistor 12 is on and the PNP transistor 13 is off, signal A is blocked and signal B passes.
Signal B is output to the output terminal 17. That is, when the switch 2° is ON, signal A is output, and when it is OFF, signal B is output.

In the embodiment, the emitter is connected to the ground and the collector is connected to the signal side, but the emitter may be connected to the signal side and the collector may be connected to the ground.

Effects of the Invention As described above, the present invention connects the emitters or collectors of an NPN transistor and a PNP transistor whose collectors or emitters are both grounded to a bonding path, and connects the bases of the two transistors via a resistor. Stop valve 2
By connecting the resistor inserted between the two power supplies and the connection point of the switch, it is possible to selectively switch two signals with two transistors and one single-circuit, one-contact switch, significantly reducing the number of components. reduction is possible. Also, when one transistor is ON, no matter how high the power supply voltage is, the other transistor is always reverse biased by vBE (approximately o, esV for silicon transistors), so the reverse withstand voltage between the base and emitter is also lower than the power supply voltage. becomes irrelevant, and the effect is extremely dog-like.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a signal switching circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional signal switching circuit. 1...A signal input terminal, 2...B signal input terminal, 3-8...resistance, 12.13...
...Transistor, 17...Output terminal, 18
...Positive power supply, 19...Negative power supply, 20.
·····switch.

Claims (1)

[Claims] The collectors or emitters of the NPN transistor and the PNP transistor are grounded, and the emitters or collectors of the NPN transistor and the PNP transistor are connected to the signal path, respectively, and the bases of both transistors are connected to the positive and negative terminals via resistors. A signal switching circuit characterized by connecting a resistor inserted in series between a power supply and a switch connection point.