JPS594810B2 - Proximity switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION 10 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 the 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 together with the detection coil 15 becomes smaller. It is something to do.

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. 20 Therefore, during the time until this oscillation width rises, the oscillation width is small, just as when the object is approaching, so an erroneous output signal indicating that the object is approaching is generated. There is a risk. For this reason, it is common to provide a power supply reset circuit that prevents the output signal from being generated for a certain period of time immediately after the power is turned on, but if this reset time is set to a certain value, the following problem will occur. In other words, when the power supply voltage rises slowly, the oscillation circuit will not start oscillating unless the supplied voltage exceeds a certain level, and it will take an additional time from the start of oscillation until the predetermined oscillation width is reached. This can cause erroneous output for a very long time after power-up. In the past, if the reset time was set extremely long in preparation for this, time would be wasted if the power supply voltage suddenly rises. 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, including an oscillation circuit 11 and a 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 control type main control transistor 151, a diode 152 connected to the base of the transistor 151, a constant voltage element 153, transistors 154, 155 and a resistor 156 forming a current mirror circuit, and the transistor 151. It consists of a resistor 157 connected between the collector and the base. The voltage detection circuit 16 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 I
A bypass capacitor 21, a detection coil 22, a capacitor 23 which forms a parallel resonant circuit together with the detection coil 22, a sensitivity adjustment variable resistor 24, an integrating capacitor 25, and a timer circuit capacitor 26 are externally connected to the C circuit 1, respectively. Ru. 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 smaller, so the output signal of the output circuit 18 becomes . . . level. In other words, an NL (normal low) output is generated. Since the transistor 162 is off when the output voltage Vs of the constant voltage circuit 15 is small, the transistor 1
63 is turned on, and the timer circuit capacitor 26 is short-circuited. When the voltage Vs 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 timer circuit 17 times up, output circuit 1
No current is supplied to the output circuit 18, and after a time has elapsed, current is supplied to the output circuit 18. Therefore, when the power is turned on, the timer circuit 1r is operated from the point at which the output voltage Vs of the constant voltage circuit 15 reaches a predetermined value and the oscillation circuit 11 starts oscillating.
The current supplied from the timer circuit 17 to the output circuit 18 is stopped for a time corresponding to the time until the oscillation width of 1 becomes sufficiently large. 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 output circuit 18 The ban will be lifted. When the power supply voltage Vcc rises gradually, the timer circuit 17 is not operated until the output voltage Vs of the constant voltage circuit 15 reaches a voltage sufficient for oscillation, and the output voltage Vs is raised to a predetermined value or higher. The timer circuit 17 is operated for the first time when the timer reaches the end of the clock, and the output circuit 18 is inhibited until the timer circuit 17 reaches the time nap. Therefore, according to the circuit shown in FIG. 1, the output signal is inhibited for a necessary and sufficient set time depending on the rising speed of the power supply voltage Vcc, and it is difficult to determine how slowly the power supply voltage Vcc rises. Even if the power goes up, the power supply can be set up reliably, and time is not wasted. By the way, when the IC circuit 1 in FIG. 1 is constructed of bipolar monosilicon, the constant voltage element may be one that utilizes the base-emitter breakdown voltage BVEBO (6 to 9 V) of a transistor, or one that is formed in a separate process. A Zener diode (5.5V) 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 cannot be kept low, and the internal constant voltage Vs cannot be adjusted to the TTL level.
Therefore, by short-circuiting the power supply voltage Vcc terminal and the internal constant voltage Vs terminal and directly connecting the TTL level power supply,
Since it cannot be made usable even at L level, it is undesirable 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 threshold voltage of the constant voltage element 161 must be lower than that, so in a biberra monolithic IC, , N diodes as shown in FIG. 2 must be connected in series to equivalently function like a Zener diode. However, in this case, since each diode is constructed using a diode formed between the base and emitter of a transistor, for example, it has a temperature coefficient of about -2mV/℃, so the total voltage of N diodes is -2mV/CXN. The width coefficient is

If N=5 as shown in Figure 2, -10mV/V. The temperature coefficient is 0, and the face direction voltage per diode is 0.
．． If the voltage is 65V (At 25°C), the threshold voltage of the constant voltage element composed of five diodes will vary 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 it, and the factors that change according to the rise time of the power supply voltage Vcc become dependent on temperature, making it unstable. The purpose of this invention is to detect when the output voltage of the constant voltage circuit that supplies a constant voltage to each circuit such as the oscillation circuit has risen to a predetermined value as described above, and from this point on, the timer circuit A proximity switch is used to operate the timer circuit and reset the power until the time-up occurs. This eliminates temperature-related fluctuations in the detection level of this voltage detection and stabilizes the start timing of the timer circuit. The purpose of the present invention is to improve the temperature drift of the output voltage of a constant voltage circuit by using a circuit for the purpose of the present invention.

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 3, a resistor 158 is connected to the reference voltage Zener diode 153 connected to the base of the series-controlled main control transistor 151 of the constant voltage circuit 15, and one end of this resistor 158 is connected to the transistor 162 of the voltage detection circuit 16.
The base of the is connected. This zena diode 153
The zener current 1z flowing through changes with respect to the power supply voltage Vcc as shown in FIG. That is, when the power supply voltage Vcc rises, the zero point on the base side of the transistor 151 rises accordingly. When the potential on the base side exceeds the Zener voltage Vz of the Zener diode 153, the Zener current 1z suddenly increases. Then, the voltage generated across the resistor 158 also rises rapidly, so at this time, the voltage across the transistor 1
62 is turned on, and as a result, transistor 163 is turned off, and charging of capacitor 26 of timer circuit 17 is started. Here, the Zener diode 153 has a Zener voltage Vz of around 5.5V, and the temperature coefficient of this Zener voltage Vz is close to O (approximately -0.2 mV/C).

The potential on the base side of the transistor 162 is VBE2
(base-emitter voltage of transistor 162), the base side potential of transistor 151 is.

Therefore, the constant voltage Vs appearing at the emitter of the transistor 151 becomes (VBE, where VBE is the voltage between the base and emitter of the transistor 151).

In other words, between the base and emitter of the transistor 162,
It functions as a diode to compensate for temperature changes in the base-emitter voltage of the transistor 151, and stabilizes the constant voltage Vs. And like Suki, Zener diode 15
The fact that the temperature coefficient of the Zener voltage Vz of No. 3 is close to O means that the durability curve in FIG. 4a also hardly changes with temperature.

Also, in FIG. 3, the rising of the Zener power supply 1z is detected. Therefore, it is possible to detect the moment immediately before the constant voltage circuit 15 sends out the constant voltage Vs, so the timer circuit 17 is operated by capturing the moment immediately before a constant voltage is supplied to each circuit and each circuit starts working normally. Moreover, the power supply reset operation can be performed for only the time determined by this timer circuit 17. FIG. 5 shows a second embodiment, in which a current 1z/m of 1/Rrl of the Zener current 1z flowing through the Zener diode 153 is connected to the resistor 170 by a current mirror circuit constituted by transistors 16 & 169. It's flowing. The base of the transistor 162 is connected to one end of this resistor 170. That is, in this example, the current is 1Z/R
By turning on the transistor 162 in accordance with n, the rising portion of the Zener current 1z is detected. FIG. 6 shows a third embodiment. In this figure? When the zener current 1z suddenly increases and the transistor 162 turns on, the transistor 1
71 is turned on and a collector current flows, and this collector current is determined by the voltage Vs, the value of the resistor 182, and the characteristics of the diodes 172 to 176. The collector current of the transistor 171, which is thus determined as a constant current, flows through the diodes 176 to 178,
A current of 1/lightning is generated by a current mirror circuit constituted by a transistor 179 and resistors 183 to 185, and this current flows to the collector of the transistor 1T9. A current approximately equal to the collector current of this transistor 179 flows through transistors 180 and 181 forming a current mirror circuit.
flows out from the collector of transistor 181 due to the action of . The collector current of this transistor 181 is used as a charging current for the timer circuit capacitor 26. That is, in the embodiment shown in FIG. 6, after the voltage detection circuit 16 detects the voltage, the timer circuit capacitor 2
The configuration is such that a constant charging current is supplied to 6. However, in the circuit shown in Figure 6, the diodes 172~ are connected in series.
Reference numeral 175 is for compensating current changes due to resistance changes due to the widths of the resistors 182 to 184. In addition to the embodiments shown in FIGS. 3, 5, and 6 above, the power supply voltage V
TT directly by shorting the cc terminal and the internal constant voltage s terminal.
When the L level power supply is connected and used, the Zener current 1z does not flow through the Zener diode 153, so in this case, although not shown, the terminal to which the timer circuit capacitor 26 should be connected and the terminal for the internal constant voltage Vs are connected. A resistor is connected between the two and the timer circuit capacitor is charged through this resistor.

According to the invention described in the embodiments above, the power supply is set until a certain period of time elapses after the output voltage of the constant voltage circuit reaches a predetermined value at which the oscillation circuit starts oscillating. The power supply reset time can be changed according to the rise of the power supply voltage, and power supply reset can be performed reliably and without wasted time.

Moreover, the constant voltage circuit is composed of a series-controlled main control transistor and a Zener diode, one end of which is connected to the base of this transistor, and the voltage detection circuit is composed of a Zener diode, one end of which is connected to the other end of the Zener diode. It consists of a resistor and a detection transistor whose base is connected to the connection point between the Q low resistor and the Zener diode, and whose emitter is connected to the other end of the resistor. Fluctuations can be removed to stabilize the start timing of the timer circuit, and the voltage between the base and emitter of the detection transistor can be used to offset the voltage between the base and emitter of the series-controlled main control transistor. Therefore, the output voltage of the constant voltage circuit becomes approximately equal to the Zener voltage of the Zener diode, and temperature drift of the output voltage of the constant voltage circuit can be prevented.

[Brief explanation of the drawings] Fig. 1 is a circuit diagram showing a conventional example, Fig. 2 is another conventional example.
3 is a circuit diagram showing a first embodiment of the present invention; FIG. 4 is a graph showing the characteristics of voltage Vcc and current 1z in FIG. 3; FIGS. 5 and 6 2A and 2B are circuit diagrams showing second and third embodiments, respectively. 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, 151...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 the constant voltage circuit that generates a predetermined output voltage. A voltage detection circuit detects that the voltage has reached the specified value, and a timer operation is started when the output voltage of the constant voltage circuit reaches or exceeds a predetermined value, and the voltage is controlled by the voltage detection circuit. In a proximity switch comprising a timer circuit configured to release the inhibition of the output circuit, the constant voltage circuit comprises a series-controlled main control transistor and a Zener diode having one end connected to the base of the transistor. , the voltage detection circuit includes a resistor having one end connected to the other end of the Zener diode, a base thereof connected to a connection point between the resistor and the Zener diode, and an emitter thereof connected to the other end of the resistor. A proximity switch comprising: a detection transistor;