JPS5953652B2 - Proximity switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency oscillation type proximity switch, and more particularly to a proximity switch of a circuit suitable for fabrication into a bipolar monolithic IC.

A high-frequency oscillation type proximity switch detects an object by utilizing the fact that when an object such as a metal approaches the detection coil, the oscillation width of the oscillation circuit formed with the detection coil becomes smaller. be.

By the way, when the power is turned on, the oscillation width of the oscillation circuit does not rise immediately after the power is turned on, but rises with a slight delay.

Therefore, during the time until the oscillation width rises, the oscillation width is small, just as when the object is approaching, so there is a risk that an erroneous output signal indicating that the object is approaching may be generated.

For this reason, it is common practice to provide a power supply reset circuit that does not generate an output signal for a certain period of time immediately after the power is turned on, or if this reset time is set to a certain value, the following problem will occur.

In other words, when the power supply voltage rises gradually, the oscillation circuit will not start oscillating unless the supplied voltage reaches a certain level, and it will take more time to reach the predetermined oscillation width after starting oscillation. , erroneous output may occur for a very long time after power-up.

Therefore, if the reset time is set to be extremely long in preparation for this, time will be wasted if the power supply voltage suddenly rises next time.

In order to solve this problem, the inventors of the present invention have already invented a proximity switch circuit as shown in FIG.

In FIG. 1, the part surrounded by the two-dot chain line 1 is the circuit part to be integrated into an IC, and the oscillation circuit 11. Comparator 1
2. Integrating circuit 13, comparator 14, constant voltage circuit 15
, a voltage detection circuit 16, a timer circuit 17, and an output circuit 18.

The constant voltage circuit 15 includes a series-controlled main control transistor 151
, a diode 152 connected to the base of this transistor 151, a constant voltage element 153, transistors 154, 155 and a resistor 156 that constitute a current mirror circuit, and a resistor 157 connected between the collector and base of the transistor 151. It is configured.

The voltage detection circuit includes a constant voltage element 161 and a transistor 162
- 167, transistors 164, 165 and transistors 166, 167 each constitute a current mirror circuit, and supply a constant current to the collector of transistor 162 and the base of transistor 163.

This IC circuit 1 includes a bypass capacitor 21 and a detection coil 22.
, and a capacitor 23, a sensitivity adjustment variable resistor 24, an integrating capacitor 25, and a timer circuit capacitor 26, which constitute a parallel resonant circuit together with the detection coil 22, are each externally attached.

Normally, when no object approaches the detection coil 22, the oscillation width of the oscillation circuit 11 is large, so no output signal is generated from the comparator 14, and the output signal from the output circuit 18 is at a low level.

When detecting that an object is close to the detection coil 22, the oscillation width of the oscillation circuit 11 becomes small, so that the output signal of the output circuit 18 becomes high level.

In other words, an NL (normal low) output is generated.

When the output voltage of the constant voltage circuit 15 is small, the transistors 1 to 162 are off, so the transistors 1 to 163 are off.
The power is turned on, and the timer circuit capacitor 26 is short-circuited.

When the voltage V5 reaches a predetermined value or more, the transistor 162 is turned on and the transistor 163 is turned off, so that the timer circuit capacitor 26 starts charging and the timer circuit 17 starts its timer operation.

Before the timer circuit 17 times up, no current is supplied to the output circuit 18, and after the timer circuit 17 times up, current is supplied to the output circuit 18.

Therefore, when the power is turned on, the output voltage of the constant voltage circuit 15 is
5 reaches a predetermined value and the oscillation circuit 11 starts oscillating, the timer circuit 17 is operated, and the output circuit 18 is operated from the timer circuit 17 for a time corresponding to the time until the oscillation width of the oscillation circuit 11 becomes sufficiently large. The current supplied to the device is stopped and prohibited.

With this configuration, when the power supply voltage Vcc rises sharply, the timer circuit 17 immediately operates, and after a certain period of time determined by the timer circuit 17, the inhibition of the output circuit 18 is released. become.

When the power supply voltage Vcc rises slowly, the timer circuit 17 is not operated until the output voltage V5 of the constant voltage circuit 15 reaches a voltage sufficient to oscillate, and the output voltage 5 becomes higher than a predetermined value. In this case, the timer circuit 17 is operated for the first time, and the output circuit 18 is prohibited until the timer circuit 17 times out.

Therefore, according to the circuit shown in FIG. 1, the power supply voltage V
It is necessary and sufficient depending on the rising speed of cc.
The output signal is inhibited for a period of .about.~, and no matter how slowly the power supply voltage Vcc rises, a reliable power supply reset can be applied, and time is not wasted.

By the way, when the IC circuit 1 in FIG. 1 is constructed of bipolar monolithic, the constant voltage element is the base-emitter breakdown voltage BVEBO (6-
9V) or a Zener diode (5.5V) formed in a separate process can be used.

When BVEBO is used as the constant voltage element 153,
The lowest value of the power supply voltage Vcc in the usable range is too low, and the internal constant voltage (2) cannot be adjusted to the TTL level.

Therefore, short-circuit the power supply voltage Vcc terminal and the internal constant voltage terminal and directly connect the TTL level power supply.
Since it cannot be made usable even at L level, it is not desirable to be subject to restrictions on use.

On the other hand, when the constant voltage element 153 is configured with the latter Zener diode (5.5V), the constant voltage element 161
The threshold voltage of the IC must be lower than that, so for bipolar monolithic ICs, N diodes must be connected in series as shown in Figure 2 to act like Zener diodes. Must be.

However, in this case, since each diode is constructed using a diode formed between the base and emitter of a transistor, it has a temperature coefficient of about -2 mV/°C, so the total N diodes have a temperature coefficient of -2 mV/°C. '(: Temperature coefficient of XN.

As shown in Figure 2, when N = 5, the temperature coefficient is -10 mV/'C, and the forward voltage per diode is 0.
, 65V (at 25°C), the threshold voltage of the constant voltage element composed of five diodes changes greatly from 3.90V to 2.65V in the temperature range of -40°C to 85°C.

Therefore, the longer the rise time of the power supply voltage Vcc, the longer it takes to detect the power supply voltage Vcc.
The factor that changes according to the rise time of c becomes unstable because it depends on the temperature.

An object of the present invention is to improve the variation in the detection level of a voltage detection circuit due to temperature, thereby eliminating variations in the startup timing of a timer circuit and the resulting instability of the power supply reset time due to temperature. The purpose of the present invention is to provide a proximity switch.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 3, a transistor 301 serves as a main control transistor of a series-controlled voltage stabilizing circuit, and a Zener diode (5.5V) 309 is connected to its base.

Transistors 302 and 303 and resistors 313 and 314 form a current mirror circuit that is a constant current source that constitutes a bias circuit for transistor 301.

Further, the transistors 304 and 305 constitute a current mirror circuit together with the resistors 311 and 312 and the resistor 303, and send a constant current (reference current) Io to the base of the transistor 306.

A transistor 306 is a transistor for controlling a timer circuit capacitor (not shown) in the timer circuit 17 in FIG.

The base of this transistor 306 has a transistor 30
A current mirror circuit consisting of 7,308 is connected, and the current I is approximately equal to the current I2 flowing through the Zener diode 309.

I'm trying to branch out more.

In the circuit shown in FIG. 3, the current flowing through the collector of the resistor 302 is I3, and the current flowing through the resistor 314 is I4, I.
If the current flowing through the emitter of the transistor 303 is I1 (m, n; constant), then, if the output voltage 5 of the constant voltage circuit becomes constant, the current IL also becomes constant, so the change in the current I4 flowing through the resistor 314 is Only current I.

increases or decreases, and a constant reference current I with the characteristics shown in FIG.

can be obtained.

The above will be explained in more detail.

First, the base-emitter voltage VBE of the transistor is V
BE= (kt/q) stone (IE/Io) where kt/Q
: Thermal voltage IO; Represented by reverse saturation current.

Therefore, considering the current mirror circuit shown in Figure 6, if the characteristics of each transistor are the same, then IEI・R1=VBE2 VBEI - (kt/q) In (IE2/IEI) Furthermore, assuming that the base current is sufficiently small. , IEI Hong ICI, IE2
Hong IC2 Therefore, ICI-R] - (kt/Q) stone (I C2/ I cl
).

In the above example, ■c1−I3, IC2=I4×,
and since R1 is the value of the resistor 313, I3・R,
= (kt/Q) stone (I4 +I L/I3).

Therefore, from this equation, the power supply voltage Vcc, the value of Zener diode 309, the value of resistors 313 and 314, and the current
, the value of the current I3 is determined.

In other words, it can be determined using the ■BEIC curve shown in FIG.

From the above, there is a relationship between I3 and ■4+IL, which can be expressed as I3=(IL+I4)7m (m is a constant) as described above.

Furthermore, in a current mirror circuit consisting of four transistors as shown in Fig. 8, assuming that the characteristics of each transistor are well matched, from the figure, IF5・R3= V BF2 V BF2-(kt/
Q) Stone (■,.

/ I]E, 3) IF5・R4-VBE3 VBE
4 = (kt/q) stone (I E3/I E4).

Assuming that the base current is sufficiently small, IE4″; Ic4,
I E2# I C2, so IF5 ・R3-(kt/Q) In (IC2/
IF5) IC, -R4= (kt/q) stone (I E3/
IC4).

If IC2 is determined by the former formula, IF5 is determined, and ■ from the latter formula.

4 is decided. In the above example, ■o4-Io, I C
2-I t+I4, and as explained above, I4+■1.
, is associated with I3, so as mentioned above, ■.

It is expressed as =■3/n.

Due to the current mirror circuit of transistors 307 and 308,
The current ■.

A current approximately equal to the current I7 flowing through the Zener diode 309 flows into the collector of the transistor 308.

Therefore, assuming that the current flowing into the base of the transistor 306 is 18, the following relationship holds: IB=IOIZ.

Therefore, when the voltage V5 does not reach a constant voltage and l2=0, the transistor 306 is on, and when the voltage V5 becomes a constant voltage and the current ■2 increases and the current ■2 becomes almost equal to 1 degree, the transistor 306 is on. Transistor 306 is turned off because base current IB disappears.

That is, the current 7 increases as shown in FIG. 4 according to the power supply voltage Vcc, and the power supply voltage Vcc becomes the voltage V.

When the current ■2 reaches the current ■. , and the transistor 306 is turned off.

Since the current (2) flowing through the Zener diode 309 increases rapidly when the output voltage (2) attempts to reach a constant voltage, this current (17) and the reference current (2).

By comparing the reference current I.

Even if there is some variation in the voltage detection level V.

The fluctuation in will be extremely small.

Also, the Zener diode 309 has a diameter of about 5.5 as described above.
Since it is a Zener diode with a threshold voltage of 309, the temperature coefficient is almost equal to O.
I, V, 7:) Bases of transistors 301 and 307
Since the emitter voltage is VBEIξVBE7, the V5 slope is V2, and the voltage detection level is ■.

The temperature change will also be extremely small.

In addition, when a TTL level power supply is used by short-circuiting the terminal of the power supply voltage Vcc and the terminal of the internal constant voltage (5), the current (2).

Since neither the current nor the current I2 flows and the transistor 306 is turned off, it is possible to use a power supply at just TL level.

Based on the above, the operation of the entire circuit in FIG. 3 will be briefly explained. When the power supply voltage Vcc is applied, a current 4 flows through the transistor 303 to the resistor 314, and this current I4 causes a current 3 to flow ( 3=Yamaju IL) 7m
), the transistor 301 is driven, voltage ■5 rises, and current ■ flows due to the loads (oscillation circuit 11, comparators 12, 14, integrating circuit 13, timer circuit 17, etc.) connected to ■5.

Then, the current I3 increases further, but when the voltage at the ■5 terminal rises and enough current is supplied to the load, the current I3 increases.
stops increasing.

Therefore, the resistor 314 is initially set to the transistor 301.
It is sufficient to supply the kind of current that drives the .

Then, as (4) and (2) increase and I3 increases, Io also increases, so that the transistor 306 is turned on.

When the power supply voltage Vcc increases and becomes higher than the Zener voltage of the Zener diode 309, a current 2 flows.

The value of these 17 is ■. When the value becomes larger than , the base current IB=IoIz of the transistor 306 stops flowing, and the transistor 306 is turned off.

FIG. 5 shows a second embodiment, in which the reference current is ■.

The circuit for making this is different from that shown in Figure 3.

In this circuit of FIG. 5, transistors 501, 502.5
03, resistors 511 and 512 constitute a current mirror circuit,
Together with the resistor 513, it constitutes a bias circuit for the transistor 301.

The L transistors 504 and 505 and the resistors 514 and 515 form a current mirror circuit for current feedback.

The other circuit configurations are the same as in FIG. 3, so the same parts are given the same numbers and the explanation will be omitted.

In the circuit shown in FIG. 5, the current flowing through the resistor 515 is I, the current flowing through the collector of the transistor 504 is 11, the base bias current of the transistor 301 is I2, and the collector current of the transistor 501 is I.

Then, I, = i/m Io-11/n (m, n; constant) n-R1/R2 (R1, R2; respective values of resistors 511, 512) holds, so ■o-I/mn, ■ Constant reference current.

It can be seen that the following can be obtained.

In the circuit shown in FIG. 5, when power supply voltage Vcc is applied, transistor 301 is driven by the current flowing through resistor 513, and voltage V5 increases.

Then, current ■ flows through the resistor 515 and the transistor 505, which causes the transistors 505 and 505 in the current mirror configuration to
504 and the resistor 514, a current of 1 is applied to the transistor 504.
1 flows.

This current 11 causes a current to similarly flow through the transistor 503, and the drive current 2 of the transistor 301 increases.

Accordingly, the current I.

also increases, turning on transistor 306.

When the power supply voltage Vcc becomes higher than the Zener voltage of the Zener diode 309, current flows through the Zener diode 309, turning off the transistor 306 as in FIG.

As described above with respect to the two embodiments, the proximity switch according to the present invention includes an oscillation circuit formed including a detection coil, a signal processing circuit that generates an output signal depending on the amplitude of the oscillation circuit, and an output circuit. , a constant voltage circuit, a voltage detection circuit that detects that the output voltage of the second constant voltage circuit has reached a predetermined value, and a second voltage detection circuit, so that the output voltage of the constant voltage circuit is controlled to a predetermined value. The power supply reset time can be controlled according to the rise state of the power supply voltage because the timer circuit is configured to start a timer operation when the value exceeds the value, and release the inhibition of the output circuit after the time has expired. .

In other words, if the power supply voltage rises quickly, the timer operation starts earlier to release the power supply reset, and if the power supply voltage rises later, the timer operation starts later and the power supply reset is released. It can be extended until it stabilizes.

Therefore, depending on the individual case, the power reset time can be set so that it is not too short or too long, so that the power reset time is time-efficient and ensures that erroneous outputs are not output. You can reset the power.

Furthermore, in addition to this configuration, the constant voltage circuit includes a series-controlled main control transistor and a Zener diode connected to the base of this transistor, and the voltage detection circuit includes a series-controlled main control transistor. a first current mirror circuit comprising a first transistor and another second transistor connected in series and applying an output current of the second transistor to a base of the series-controlled main control transistor; transistor and other third
, a second current mirror circuit including a fourth transistor; and a fifth current mirror circuit to which a current flowing to the Zener diode is supplied.
and a sixth transistor to which the output current of the fourth transistor of the second current mirror circuit is supplied;
The current mirror circuit compares the output current of the fourth transistor of the second current mirror circuit with the current flowing through the Zener diode, and when the latter becomes larger than a certain value based on the former, the Since the timer circuit is activated assuming that the output voltage of the voltage circuit has exceeded a predetermined value, it is possible to improve the fluctuation of the detection level of the voltage detection circuit depending on the temperature.

Therefore, it is possible to eliminate fluctuations in the activation timing of the timer circuit, and to prevent the power supply reset time from becoming unstable due to temperature, which is caused by this fluctuation.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional example, FIG. 2 is a circuit diagram showing a part of another conventional example, FIG. 3 is a circuit diagram showing the second embodiment of the present invention, and FIG. Current I2 and current I in Figure 3. FIG. 5 is a circuit diagram showing the second embodiment. FIGS. 6 to 8 are for explaining the operation. FIGS. 6 and 8 are circuit diagrams, and FIG. is a graph representing the base-emitter voltage-collector current characteristics of a transistor. 11...Oscillation circuit, 12.14...Comparator, 13...Integrator circuit, 15...
... Constant voltage circuit, 16 ... Voltage detection circuit, 17
...Timer circuit, 18...Output circuit,
22...Detection coil, 301...Series control type main control transistor.

Claims (1)

[Claims] 1 An oscillation circuit formed including a detection coil, a signal processing circuit that generates an output signal depending on the magnitude of the amplitude of this oscillation circuit, an output circuit, a constant voltage circuit, and an output voltage of this constant voltage circuit. A voltage detection circuit that detects that a predetermined value has been reached; and a timer operation that is controlled by the voltage detection circuit and starts a timer operation when the output voltage of the constant voltage circuit exceeds the predetermined value, and after the time has elapsed, the output circuit is controlled by the voltage detection circuit. In the proximity switch, the constant voltage circuit includes a series-controlled main control transistor and a Zener diode connected to the base of the transistor, and the voltage detection circuit is composed of a first transistor and another second transistor connected in series to the series-controlled main control transistor, and a first transistor that applies the output current of the second transistor to the base of the series-controlled main control transistor. 1 current mirror circuit;
a second current mirror circuit including the first transistor and other third and fourth transistors; a fifth transistor to which a current flowing to the Zener diode is supplied; and a fifth transistor of the second current mirror circuit; and a sixth transistor supplied with the output current of the fourth transistor, and the output current of the fourth transistor of the second current mirror circuit is controlled by the third current mirror circuit. and the current flowing through the Zener diode, and when the latter becomes larger than a certain value based on the former, the timer circuit is activated, assuming that the output voltage of the constant voltage circuit has exceeded a predetermined value. A proximity switch characterized by: