JPS584279Y2 - electronic switch circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic switch circuit that selectively outputs one input signal to two output terminals.

This type of electronic switch circuit is widely used in transmitting/receiving switching circuits of transceivers and other applications.The principle of this circuit is, as shown in Figure 1, an NPN t-transistor whose base and collector are commonly connected to the input terminal A. Q1 and PNP transistor Q2 respectively at output terminals B1. B2, and each transistor Q1. The base current of Q2 is made to flow selectively, thereby selectively making transistors Q and 11Q2 conductive.

That is, if the switch SW is opened as shown in Fig. 1,
Current from the input terminal passes through resistor R1 to transistor Q1.
flows into the base of transistor Q1, causing its transistor Q1 to conduct.

At this time, transistor Q2 is in a cutoff state with no base current flowing through it.

Furthermore, when switch SW is closed, the base of transistor Q2 is pulled close to the ground potential, so that transistor Q2 becomes conductive.

Transistor Q1 does not become conductive because its base potential is close to ground potential.

In other words, since a load is normally connected to the output terminal B1,
The threshold voltage provided by diode D1 is not directly applied between the base and emitter of transistor Q1.

However, in FIG. 2, where switch SW is replaced with transistor Q3, a certain amount of potential is generated at point a in the region where transistor Q3 is not completely conductive, and therefore not only transistor Q2 but also transistor Q1 is conductive. The original switching function may be impaired.

The present invention has been developed in view of this point, by detecting the conduction of one transistor and forcibly shutting off the other transistor using the detection completion signal, thereby solving the above-mentioned problems. It is an object of the present invention to provide an electronic switch circuit that avoids this problem.

Hereinafter, an embodiment of the present invention will be described with reference to FIG. 3 and subsequent figures. In FIG. 3, an NPN l-transistor Q4 is connected in parallel to a capacitor C for base bias of a transistor Q1, and its base is It is connected to the output w32 via a diode D2 and a resistor R3.

Therefore, in this circuit, even in a region where transistor Q3 is not completely conductive, if transistor Q2 is conductive, its output is detected, transistor Q4 is conductive, and the base potential of transistor Q1 is set to approximately ground potential (more precisely, the transistor The potential between the collect emitter of Q4 is 0
．． (approximately 2V), the transistor Q1 will not become conductive.

Figure 4 shows a Zener diode ZD instead of capacitor C.
This is another embodiment in which the transistor Q1 is biased using the transistor Q1.

Also, the above is about negative grounding, but to make positive grounding, as shown in Figure 5, each transistor Q'l
~Q'4 may be of opposite polarity.

As described above, according to the present invention, one input signal can be reliably output alternatively to two outputs.

[Brief explanation of drawings]

FIG. 1 is a basic circuit diagram of an electronic switch, FIG. 2 is a conventional circuit diagram, and FIGS. 3 to 5 are circuit diagrams of this embodiment.

Claims (1)

[Scope of utility model registration request] A series connection portion of a first transistor of PNP and a second transistor of NPN is connected to an input terminal, and the other terminal is connected to each separate output terminal, and the first and second transistors are connected by cutting off the third transistor. In an electronic switch circuit that makes one of the transistors conductive and makes the other conductive due to the conduction, detecting the output of the other of the first and second transistors that is made conductive due to the conduction of the third transistor, An electronic switch circuit that forcibly shuts off one of the second transistors.