JPH03203408A - Electric switch circuit - Google Patents

Abstract

PURPOSE:To obtain exact switching operation even at the time of a low voltage by connecting a bias lower than a reference bias source connected to the base of the 2nd transistor(TR) by a base-emitter voltage to the base of the 1st TR to be driven by an input signal. CONSTITUTION:The emitter of a TR Q7 whose base is connected to the reference voltage V1 is connected to the base of a TR Q1 and voltage more than V2=V1-VBE is always impressed to the base of the TR Q1. The base of the TR Q1 is connected to an input terminal through a resistor R and an input signal V3 is inputted to the input terminal. Both the TRs Q1, Q2 are differential amplifiers, and when (input signal V3)<(reference voltage V1), (base voltage V2 of TR Q1=V1-VBE)<(reference voltage V1) is formed, the TR Q1 is driven and current I is allowed to flow from the emitter of a TR Q3 to a low level output terminal L through a TR Q4. At the time, the base potential of the TR Q1 is fixed at V2=V1-VBE through input signal V3=GND, the TR Q1 can output the current I.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electronic switch circuit using a transistor as a non-contact switch, such as an electronic switch used as a part of an electronic switching device in a television or a video tape recorder. 6 Related to Circuits [Prior Art] Televisions and video tape recorders in recent years are equipped with electronic switching devices to control the image and audio conditions in various ways. The switching device is activated.

The electronic switch circuit used in this pillar switching device is constructed using a plurality of transistors as non-contact switches, and utilizes a function in which the transistors perform 0N10FF operation by changing the base voltage with respect to the emitter.

For example, a circuit shown in FIG. 2 is conventionally known as this type of switch circuit.

In FIG. 2, Ql, Q2 and Q8, Q9 are transistors that are differentially connected to each other, and the transistor Q
A reference bias V1 is applied to the base of transistor Q9, and an external input is applied to the base of transistor Q9 via a protection resistor R at a switch terminal. transistor Q1,
A constant current source I is connected to the common emitter of Q2,
The collector of transistor Q1 is connected to the base of transistor Q3 and the collector of transistor Q4, and the emitter of transistor Q4 is connected to GND. And the emitter of transistor Q3 is transistor Q
It is connected to the base of 4 and becomes the low level output end.

Further, the base of a transistor Q5 and the collector of a transistor Q6 are connected to the collector of the transistor Q2, and the emitter of this transistor Q6 is connected to GND. The emitter of the transistor Q5 is connected to the base of the transistor Q6 and becomes a high level output terminal H.

The collectors of these transistors Q3 and Q5 are common and connected to a power source connected to one end of the constant current source.

The current flowing through transistor Q1 is changed from 1 to transistor Q4 by transistors Q3 and Q4 of the Wilson type constant current source.
The current flowing through the transistor Q2 also flows to the high level output terminal H, which is the base of the transistor Q6, by transistors Q5 and Q6 of the Wilson type constant current source.

Next, the operation will be explained.

When the external input voltage is higher than the reference voltage (1), transistors Q8 and Q2 are turned on, a constant current flows through transistor Q6, and an output appears at the high-level output terminal H. Further, when the external input voltage is lower than the reference voltage V1, the transistors Q9 and Ql are ONL, a constant current I flows through the transistor Q4, and an output appears at the high level output end.

[Problem to be solved by the invention] However, in this case, the transistor Q4, that is, the transistor responsible for the low level output end, is the transistor Q3, Q4.
Since the transistor is a Wilson type constant current source, the collector voltage of the transistor Q1 is required to be 14V or more since the base-emitter potential Vag of the transistors Q3 and Q4 is 7V.

Note that in order for current to flow between the base and emitter of a normal transistor, a minimum of Vm*=0, 7 V is required.

Therefore, there was a problem that the external input voltage could not be lower than 0.7V.

The present invention has been developed under such circumstances, and an object of the present invention is to provide an electronic switch circuit in which setting of a switching instruction voltage is extremely simple and reliable switching operation can be obtained.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a method in which a reference bias source V1 connected to the base of the second transistor is connected to the base of the second transistor operating in the input signal. By connecting a bias that is as low as the base-emitter voltage ■, the base of the first transistor remains at V even if the input signal drops to GND.

The bias value becomes -VB, and the first transistor can maintain a normal state.

[Function] The present invention equipped with such a means is effective when the input signal level is G.
Since normal switch operation can be performed even when the voltage drops to ND, the switching level can be set more freely than in conventional switch circuits.

[Example] Hereinafter, the present invention will be explained using the drawings.

FIG. 1 is a diagram showing an embodiment of an electronic switch circuit according to the present invention. The configuration is that the emitter of a transistor Q7 whose base is connected to the reference voltage v1 is connected to the base of the transistor Q1 of the conventional example shown in FIG. has been added. In Figure 1, transistor Q
The point from the base of 1 through the resistor R is the input terminal, and the input signal V3 is input to the input terminal.

Transistors Q1 and Q2 are differential amplifiers (input signal V
3) In the case of < (reference voltage V,), (base voltage of transistor Q1 2 = Vl - VB!: + < (reference voltage V), the transistor Ql operates 1, and the transistor Q1 is switched from the emitter of transistor Q3 to A current I flows to the low level output terminal via Q4.At this time, even if the input signal v3=GND, the base potential of the transistor Q1 is fixed at V2=Vk, so the transistor Q1 flows through the current I. Can be output.

Next, when (input signal V3) > (reference voltage V4), transistor Q7 is turned off, and (base voltage V of transistor Q1, = V3) > (reference voltage V, ),
The transistor Q2 operates, and a current flows from the emitter of the transistor Q5 to the high-level output terminal 11 via the transistor Q6.

[Effects of the Invention] As described above, according to the present invention, the normal switching operation is performed even when the input signal is low, so that the allowable value of the input voltage can be widened, and accurate switching operation can be obtained even at low voltage.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an electronic switch circuit according to the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional switch circuit. Transistor Q1...First transistor Q2...
2nd Q3...3rd Q4...4th Q5...5th Q6...6th Q7...7th Q8...8th Q9...3rd 9 Constant current work...First constant current source, GND...Ground potential, Resistor R...Resistor, Reference voltage■...Base voltage of transistor Q2, Base Q current FIEVz...Transistor Base voltage of Q1, human power signal Vyu...input terminal.

Claims (1)

[Claims] A first constant current source consisting of a first transistor and a second transistor that constitute a first differential amplifier, and a third transistor and a fourth transistor that operate when the first transistor operates. a second constant current source configured of a fifth transistor and a sixth transistor that operate when the second transistor operates; a first bias source connected to the base of the second transistor; A first bias source is connected to the base and a first bias source is connected to the emitter.
An electronic switch circuit characterized in that the lowest bias of the first transistor is determined by a seventh transistor to which the base of the transistor is connected.