JPH0160972B2 - - Google Patents

Description

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

Touch switches, which are operated by a person's touch by using 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, where Q ₁ and Q ₃ are npn transistors, and Q ₂ and Q ₄
is a pnp transistor, R ₁ , R ₂ , R ₃ , R ⁴ are resistors,
R _T is the resistance between the ground caused by touching the human body, Vcc ₁ and Vcc ₂ are the power supply, T is the touch board,
RM is an input terminal, and Y is an output terminal.

In FIG. 1, when a resistor R _T is connected between the touch plate T and the ground due to a human body, etc., the transistors Q ₂ ,
It is sequentially amplified by Q ₃ and Q ₄ and an output voltage is generated at the output terminal Y.

Also, when a signal that makes transistor Q ₁ conductive is applied to the input _terminal RM instead of resistor RT, transistor Q ₁ becomes conductive and the base current of transistor Q ₂ is supplied, so that resistor _RT is turned on. Board T
yields similar results as connected to .

This electrical signal to input terminal RM is used for remote control.

Now, in this circuit configuration, if the collector-emitter leak current of transistor Q ₂ (hereinafter referred to as I _CEO2 ) and the collector-emitter leak current of transistor Q ₁ (hereinafter referred to as I _CEO1 ) increase the touch sensitivity, The more you do it, the more it becomes a problem. In other words, increasing touch sensitivity, in other words, allowing the circuit to operate normally even when resistor R _T has a high resistance, requires that the base current of transistor Q ₂ and, by extension, the collector current become extremely small.
I It becomes difficult to distinguish it from _CEO2 . This thing is
Considering the temperature dependence of I _CEO2 , its operation at high temperatures becomes extremely unstable.

These things also apply to the transistor Q _{1 that} operates in place of the resistor _RT .
I _CEO1 must be kept smaller than I _{CEO2 by the amount that I CEO1 is} amplified by transistor Q ₂ .

Ultimately, the device shown in 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-mentioned drawbacks, and it is an object of the present invention to provide a highly sensitive touch switch circuit while alleviating the restriction on transistor leakage current.

This invention will be explained in detail below using an embodiment shown in FIG.

In FIG. 2, the same reference numerals as in FIG. 1 indicate the same contents.

In Figure 2, Q ₅ and Q ₆ are npn transistors,
D ₁ to _{D 3} are diodes, and R ₅ and R ₆ are resistances.

The role of the above elements is that of conventional transistors Q ₁ and Q ₂
This allows a high-sensitivity touch switch to be easily constructed while allowing or suppressing leakage current.The operation is as follows.

When no signal is supplied to the input terminal RM, and when there is no contact with the human body or the like and there is no resistor _RT , transistors Q ₁ to _{Q 4} and Q ₆ are non-conducting, Q ₅ is conducting and is in a saturated state, and the output is No output appears at terminal Y.

When the resistor R _T is connected and the transistor Q ₂ becomes conductive, the transistors Q ₃ and Q ₄ become conductive, and an output appears at the output terminal Y.

When a signal that makes transistor Q ₁ conductive is supplied to input terminal RM without resistor _RT , this signal makes transistor Q ₆ conductive and transistor
When Q ₅ is made non-conductive, transistors Q ₂ and Q ₃ are non-conductive, transistor Q ₄ is conductive, and an output appears at output terminal Y.

In this case, the output is generated by a transistor
Although Q ₁ is disconnected from Vcc ₁ , current flows from Vcc ₂ to transistor Q ₁ via the emitter base of transistor Q ₄ , diodes D ₃ and D ₂ .

Next, the functions of each added element will be explained below. Diode D ₁ first acts as a bypass for the leakage current I _CEO1 of transistor Q ₁ and
Transistor _Q2 is prevented from being driven by _ICEO1 of _Q1 . That is, in the absence of diode D ₁ , the leakage current I _CEO1 is mainly Vcc ₁ → Q ₅ → Q ₂ →
The leakage current I CEO1 flows through the route D ₂ →Q ₁ , but by inserting the diode D ₁ , the leakage current I _CEO1 becomes Vcc ₁ → Q ₅ →
Since it flows along the route D ₁ →Q ₁ and bypasses the transistor Q ₂ , the diode D ₁ acts as a bypass for the leakage current I _CEO1 of the transistor Q ₁ . Furthermore, the forward voltage of diode D ₁ causes diode D ₂ to
By clamping between the emitter and base of transistor Q ₂ through , it serves to suppress the leakage current I _CEO2 of transistor Q ₂ to a very small value.

The diode D ₂ prevents the emitter-base of the transistor Q ₂ from being driven by the forward voltage generated by the leakage current I _CEO1 of the transistor Q ₁ flowing through the diode D ₁ ;
When resistor _RT is connected, all of the current flowing through resistor _RT becomes the base current of transistor _Q2 .

Diode D ₃ makes transistor Q ₄ conductive due to conduction of transistor Q ₁ and transfers the base current of transistor Q ₄ to the transistor through diode D ₂ .
This is a bypass diode to allow the current to flow to the collector of _Q1 .

When transistors Q ₆ and Q ₅ operate transistor Q ₄ by conduction of Q ₁ , if (Vcc ₁ ) has a certain finite value, the collector current of transistor Q ₁ will flow through diode D ₁ , Since transistor _Q4 cannot be made conductive,
Transistor Q ₆ operates simultaneously with transistor Q ₁
It also conducts _, and its collector-emitter saturation voltage causes the transistor _Q5 to become non-conductive, thereby serving to cut off the current supplied to the transistor _Q1 via the diode D1. Also, transistor Q ₁
When the output is controlled by the operation of the transistor, the output control function by the resistor R _T is stopped.
The emitter potential of Q ₂ has also started to be cut off. However, if this is not necessary, the transistor
It is obvious that the emitter of Q ₂ should be connected to the power supply of Vcc ₂ .

As described above, as a means to largely tolerate and suppress the leakage current of the transistor connected to the touch part, which is a problem in high-sensitivity touch switch circuits,
In the above embodiment, the circuit configuration of the diodes D ₁ and D ₂ ,
In addition to this circuit configuration, means for cutting off the power to the touch section and means for setting a signal bypass for controlling the output even when the power to the touch section is cut off are provided.

In addition, in this invention, equivalent parts of the PNP and NPN transistors are replaced with NPN transistors, which have a complementary relationship.
It goes without saying that it can be replaced with a pnp transistor, and that there are many applications that do not impair the spirit of the invention.

As described above, the present invention can tolerate a wide range of leakage current from the transistors of the touch switch circuit, so that a highly sensitive and stable touch switch circuit can be constructed.

[Brief explanation of drawings]

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, D ₁ is the first diode and D ₂ is the second diode.
, Q ₁ is the first transistor, and Q ₂ is the second transistor. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. The first and second polarities are complementary to each other.
transistor, and first and second diodes connected in series in opposite directions, and when the first transistor is an npn type, the cathodes of the first and second diodes are connected to each other, and the first transistor is connected in series. In the case of a pnp type, the anodes of the first and second diodes are connected to each other, and the intermediate connection point of the first and second diodes is connected to the collector of the first transistor, and the other of the first diodes is connected to the collector of the second transistor. and the other side of the second diode is connected to the base of the second transistor, respectively,
A touch switch circuit characterized in that a first input signal is applied to the base or emitter of the first transistor, a second input signal is applied to the base of the second transistor, and an output signal is obtained by driving the first or second transistor.