JPS5917492B2 - touch switch circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a touch switch circuit using a transistor that operates as a touch switch.

Touch switches, which are operated by a person touching a touch panel by utilizing the resistance between the human body and the earth, have been put into practical use in a wide range of fields because they can be easily constructed using transistor circuits.

Figure 1 shows an example of a conventional touch switch.
Ql, Q3 are the first and third npn transistors, Q2 .
Q4 is the second pnp. fourth transistor, R1, R2,
R3 and R4 are resistances, RT is the resistance between the human body and the ground caused by the human body touching the touch plate T, and Vcc l
, Vcc 2 is a power supply, RM is an input terminal, and Y is an output terminal.

In FIG. 1, when a resistor RT is connected between the touch plate T and the ground due to a human body or the like, the output of the second transistor Q2 is changed to the third transistor Q2. The output voltage is sequentially amplified by the fourth transistors Q3 and Q4, and an output voltage is generated at the output terminal Y.

Furthermore, when a control signal that makes the first transistor Q1 conductive instead of the resistor RT is applied to the input terminal RM, the first transistor Q1 becomes conductive and the base current of the second transistor Q2 is supplied, so that the resistor RT is connected to the touch plate T, yielding the same result.

This electrical signal to the input terminal RM is applied during remote control.

Now, in this circuit configuration, the collector-emitter leakage current (hereinafter referred to as 10EO2) of the second transistor Q2 is
Furthermore, the collector-emitter leakage current (hereinafter referred to as 'OEO+) of the first transistor Q1 becomes a problem as the touch sensitivity increases.

In other words, increasing the touch sensitivity, in other words, allowing the circuit to operate normally even when the resistor RT has a high resistance, is difficult because the base current and collector current of the second transistor Q2 become minute currents. It becomes difficult to distinguish between the collector current and the leakage current 10EO2.

Considering the temperature dependence of the leakage current 10EO2, this means that the operation at high temperatures becomes extremely unstable.

These things also apply to the first transistor Q1 that operates in place of the resistor RT.
The leakage current 10EO+ must be suppressed to be smaller than the leakage current 10EO2 by the amount that the leakage current 10EO+ is amplified by the second transistor Q2.

Ultimately, the circuit of FIG. 1 has the disadvantage that it is not possible to construct a highly sensitive touch switch.

The present invention has been made in view of the above drawbacks of the conventional circuit, and includes a first diode that prevents the second transistor/transistor from being driven by the leakage current of the first transistor, and a first diode that prevents the first transistor from driving when a control signal is applied to the first transistor. , by providing a power cutoff circuit that cuts off the power supply to the second transistor and a second diode that allows the emitter base current of the fourth transistor to flow through the first transistor when the power is cut off, transistor leakage current is limited. The object of the present invention is to provide a touch switch circuit with high sensitivity while reducing the noise level.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG.

In FIG. 2, the same reference numerals as in FIG. 1 indicate the same contents, and Q5. Q6 is the fifth and sixth NPN transistors constituting a power cutoff circuit, D2 and D3 are first and second diodes, and R5 and R6 are resistors.

The roles of the above elements are the conventional first and second transistors Ql,
This allows a high-sensitivity touch switch to be easily configured while allowing or suppressing the leakage current of Q2, and its operation is as follows.

When no signal is supplied to the input terminal RM, and when the human body etc. is not in contact with the resistor RT, the first to
The fourth transistors Q1 to Q4 and the sixth transistor Q6 are non-conductive, and the fifth transistor Q5 is conductive and in a saturated state, so that no output appears at the output terminal Y.

When the resistor RT is connected and the second transistor Q2 becomes conductive, the third, fourth transistors Q3 . Q4 becomes conductive and an output appears at output terminal Y.

When a control signal that makes the first transistor Q1 conductive is supplied to the input terminal RM in the absence of the resistor RT, this signal makes the sixth transistor Q6 conductive and the fifth transistor Q5 becomes non-conductive. , the supply of power supply VCCI to the second transistors Ql and Q2 is cut off,
Second and third transistors Q2. Q3 is non-conductive, the fourth transistor Q4 is conductive, and an output appears at the output terminal Y.

In this case, a current flows from the power supply Vcc2 where the output is generated to the first transistor Q1 via the emitter base of the fourth transistor Q4, the second and first diodes D3 and D2.

Next, the functions of each element added above will be explained below.

The first diode D2 is connected to the second transistor Q by the leakage current l0EO+ of the first transistor Q1.
While ensuring that the emitter-base of 2 is not driven,
When the resistor RT is connected, all the current flowing through the resistor R'T becomes the base current of the second transistor Q2.

The second diode D3 is used as a bypass to cause the base current of the fourth transistor Q4 to flow through the first diode D2 to the collector of the first transistor Q1 in order to make the fourth transistor Q4 conductive by the conduction of the first transistor Q1. It is a diode.

Fifth and sixth transistors Q5 forming a power cutoff circuit
, Q6 applies a control signal to the input terminal RM to make the first transistor Q1 conductive, thereby operating the fourth transistor Q4, and when the power supply Vcci has a certain finite value, the collector of the first transistor Q1 Since the current flows from the fifth transistor/disc Q5 and the fourth transistor Q4 cannot be made conductive, the sixth transistor Q6 is also made conductive at the same time as the first transistor Q1 is operated, and its collector-emitter saturation voltage causes the fifth transistor Q4 to become conductive. Transistor Q5 is rendered non-conductive, thereby preventing power supply Vcci from being supplied to first transistor Q1.

Further, the fifth and sixth transistors Q5. Q6 is configured to also cut off the emitter power supply of the second transistor Q2 in order to stop the output control function by the resistor RT when the output is restricted by the operation of the first transistor Q1.

However, if this is not necessary, it is obvious that it is better to connect the emitter of the second transistor Q2 to the power supply V CC2.

Although not mentioned in the above explanation, the second tiger / Jisk Q
It is obvious that the leakage current 10EO2 of the second transistor/disc Q2 is very small and does not pose a problem because the emitter and base of the second transistor/disc Q2 are short-circuited via the first diode D2.

As described above, in the above embodiment, the input circuit including the first diode D2 and this In addition to the circuit configuration, a power cutoff circuit that cuts off the power to the touch section, and a second diode D3 as means for setting a signal bypass to control the output even when the power to the touch section is cut off are provided. It is something.

In addition, in this invention, the complementary parts of the pnp and npn transistors are respectively complementary to npn and pnp.
It goes without saying that it can be replaced with a transistor and that there are many applications that do not deviate from the spirit of the invention.

As explained above, the present invention includes a first diode that prevents the second transistor from being driven by the leakage current of the first transistor, and a power source that prevents the first and second transistors from being driven when a control signal is applied to the first transistor. A power supply cutoff circuit that cuts off the power supply and a second diode that allows the emitter base current of the fourth transistor to flow through the first transistor when the power supply is cut off are provided, resulting in high sensitivity that can tolerate a wide range of transistor leakage current. This has the effect of providing a stable touch switch circuit even at high temperatures.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional touch switch circuit, and FIG. 2 is a circuit diagram showing an embodiment of the touch switch circuit of the present invention. In the figure, D2. D3 are the first and second diodes, Ql
is the first transistor, Q2 is the second transistor, Q3 .
Q4 is the third and fourth transistor that constitutes the amplifier circuit;
5. Q6 is the fifth and sixth transistors constituting a power cutoff circuit, T is a touch plate, and RT is a touch resistor. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1 a first conductivity type transistor having a base input with a control signal and an emitter connected to a second potential point of a first power supply;
a second transistor of a second conductivity type, the emitter of which is connected to the collector of the first transistor, and a touch resistor connected to the ground when touched by a human body; the base of the second transistor is connected to a touch plate; a first diode connected between the collector of the first transistor and the emitter of the second transistor and a first potential point of the first power supply; is input, a power cutoff circuit cuts off the power supply from the first power source to the first and second transistors, which is sequentially connected to the collector of the second transistor and connected to the first potential point of the second power source. an amplifier circuit having an eighth transistor of a first conductivity type and a fourth transistor of a second conductivity type connected between a second potential point and amplifying and outputting an output of the second transistor; a second diode connected between the base and the base of the fourth transistor; when a human body touches the touch plate and a touch resistor is connected between the touch plate and the ground, the base of the second transistor is connected; is grounded via a touch resistor, the second transistor is turned on and an output signal is output from the amplifier circuit, and the control signal is input to the base of the first transistor and the power cutoff circuit.
When the power supply from the first power source to the first and second transistors is cut off, a circuit consisting of the second power source, the emitter base of the fourth transistor, the second diode, the first diode, and the first transistor A current flows through the
A touch switch circuit in which the fourth transistor turns on and outputs an output signal.