JPS5842570B2 - Proximity switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a proximity switch, and more particularly to an improvement in a high frequency oscillation type proximity switch circuit.

A conventional proximity switch is constructed as shown in FIG.

In this FIG. 1, the proximity switch 1 has an IC circuit 10 and this I
A sensitivity adjustment resistor 11 externally attached to the C circuit 10. A detection coil 12, a capacitor 13 forming a parallel resonant circuit with the detection coil 12, resistors 14 and 16, and a transistor i s
, 17. It consists of a timer circuit capacitor 18 and a bypass capacitor 19.

The IC circuit 10 includes an oscillation circuit including a detection coil 12, a signal processing circuit that generates an output signal depending on the magnitude of the oscillation amplitude of the oscillation circuit, a constant voltage circuit, a timer circuit, and the like.

The timer circuit inside the IC circuit 10 includes an externally attached capacitor 18, and is configured to time out when the charging voltage of the capacitor 18 reaches a predetermined value when the power is turned on.

When the power is turned on, when this timer circuit times out, the output signal is forcibly inhibited to prevent erroneous output from being output in the unstable state when the power is turned on. I'm here.

The bypass capacitor 19 is connected to the output terminal of the constant voltage circuit inside the IC circuit 10, and prevents the oscillation output from being superimposed on the constant voltage power supply line.

In FIG. 1, when no object approaches the detection coil 12, the transistor 15 is turned off, and when an object approaches the detection coil 12, the transistor 15 is turned on.

If a relay is connected between the positive power supply terminal and the output terminal as shown by the dotted line, the relay will turn on when an object approaches.

If the current of the output signal flowing through this relay is 1, and the value of the resistor 16 is R, then a voltage of I×R will be generated at both ends of the resistor 16.

Here, the base-emitter voltage of transistor 17 is V
Assuming that BE, the transistor 17 is turned on when the current 2 increases to 1 which satisfies VBE=IR.

Then, a part of the base current of transistor 150 flows through this transistor 17, so that the current size is limited.

In this way, the circuit consisting of the resistor 16 and the transistor 17 is
It works to protect the circuit when an excessive current of the output signal flows and attempts to destroy the transistor 15 etc. when a load such as a relay is short-circuited.

By the way, assuming that the switching current of the normal transistor 15, that is, the switching current of the proximity switch 1, is 200 mA, the VBE of the transistor 17 is 0.5 to 0 depending on the temperature.
．． Since we want to make it change between 7V and at least 200mA, the value of resistor 16 is 0.5R, so it must satisfy the relationship R<-=2.5[,Q].
．． 2 Must be.

Therefore, if this resistance value R is 2.2 [, Q), when ■BE = 0.5 [■], the limiting current ■ = 227 (JT
IA) ■When BE=0.7 [■], it becomes 318 (mA).

Therefore, between the positive and negative power terminals of the proximity switch 1, 24
[V] is applied, and the maximum loss of the transistor 15 (when the load is short-circuited) is 7.63 (lVv), H24 [v
] X O, 318['A'l becomes transistor 15
In order to withstand the above-mentioned loss, an element with a large wattage is required, which results in a large size and also generates a large amount of heat as the proximity switch 1. In view of the above, the present invention eliminates the need to use an element with a large wattage as an output transistor. It is an object of the present invention to provide a proximity switch which has the same protective function as described above while reducing heat generation during a short circuit, and which also solves problems peculiar to IC implementation.

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

As shown in FIG. 2, the proximity switch 2 has a detection coil 12, a capacitor 13, an NPN output transistor 15, a flow detection resistor 16, a timer circuit capacitor 18, and a bypass capacitor 19 externally attached to the IC circuit 21. It is composed of

Note that the sensitivity adjustment resistor 11 is omitted. IC circuit 21
are a detection circuit 22, a constant voltage circuit 23, and a current detection circuit 24.
．． It is composed of a timer circuit 25, an output circuit 26, and the like.

The detection circuit 22 includes an oscillation circuit formed together with the detection coil 12, and a signal processing circuit that generates a detection signal in response to changes in the oscillation width of the oscillation circuit.

The constant voltage circuit 23 is for sending a constant voltage Vs to each circuit.

The current detection circuit 24 detects the current flowing through the constant voltage circuit 23 and detects that the constant voltage circuit 23 has entered the constant voltage operation region and outputs a predetermined voltage Vs.

Timer circuit 25 operates in response to current detection circuit 24 .

That is, before the constant voltage circuit 23 outputs the constant voltage Vs, the capacitor 18 is short-circuited, and after the constant voltage circuit 23 outputs the constant voltage Vs, the capacitor 18 is not charged. is now being carried out.

Then, a timer operation is performed for a certain period of time at 1 when the charging voltage of the capacitor 18 reaches a predetermined value, and when the time reaches 1, the output circuit 26 is rendered inactive.

In this way, the power supply reset time is changed according to the rising speed of the power supply voltage Vcc, and a constant voltage ■s starts to be supplied from the constant voltage circuit 23, and after a further fixed period of time has elapsed, each circuit in the detection circuit 22 etc. Only when it is certain that it is operating normally, the output circuit 26 is brought into operation and the output signal is sent to the outside.

The timer circuit 25 specifically includes 15 transistors 1.
It is mainly composed of numbers 01 to 115.

Transistors 101-103 and transistors 104-106 each constitute a current mirror circuit, and a constant current is supplied from the collector of each of transistors 103, 105, and 106.

The transistors 107, 108, and 103 constitute a voltage comparator, which compares the charging voltage of the capacitor 18 applied to the base of the transistor 107 with the reference voltage from the resistor voltage divider circuit applied to the base of the transistor 108. When the charging voltage of the capacitor 18 is lower than the reference voltage, the transistor 107 is turned off, and when it is higher, the transistor 107 is turned on.

Transistors 111 and 112 constitute a current mirror circuit, and when transistor 107 is on, transistor 113 is turned on.

The output circuit 26 includes transistors 121 to 1 which constitute a current mirror circuit together with the transistors 111 and 112.
23 and 1 24 , 125 which constitute a current mirror circuit.
and the transistor 126.1 that constitutes the current □ error circuit.
27, and transistors 131 to 136.

Furthermore, the transistor 1330 base and this IC circuit 2
A diode 41 and a resistor 42 connected between the output terminals of
and a diode 43 connected between the base of the transistor 134 and the output terminal of this IC circuit 21.
and a series circuit with a resistor 44.

Before the timer circuit 25 times up, that is, when the charging voltage of the capacitor 18 is lower than the reference voltage and the transistor 107 is off, no current is supplied to the collectors of the transistors 121 to 123, so that the transistor 1
No current is supplied from the collector of 27 either.

Therefore, the output circuit 26 is in the same non-operating state as before the power was turned on.

When the charging voltage of the capacitor 18 becomes higher than the reference voltage and the transistor 107 is turned on, and the timer circuit 25 times up, the collectors of the transistors 121 to 123 and 127 are supplied with a stain current, so that the output circuit 26 becomes It becomes operational.

At this time, if an object approaches the detection coil 12, the detection circuit 2
Since an output signal is generated from 2, transistor 131 is turned on, and as a result, transistor 132 is turned off, so transistors 133 and 135 are turned on, and transistor 134 is turned on.
．． 136 is turned off.

Therefore, the transistor 15 is turned on, and current flows through a load such as a relay connected between the output terminal of the proximity switch 2 and the positive power supply terminal.

When an object is not approaching the detection coil 12, the transistor 131 is turned off, the transistor 132 is turned on, the transistors 133 and 135 are turned off, and the transistors 134 and 136 are turned on, so the transistor 15 is turned off, and the transistor 15 is turned off. No current flows through the load.

When the transistor 15 is turned on and current is flowing through a load such as a relay or the like, if a short circuit occurs in the load and the output signal current becomes excessive, the current detection resistor 16 The voltage across it increases, so transistor 31 turns on.

As a result, the base potential of the transistor 108 is lowered to Ov, and the reference voltage is lowered to Ov.

At this time, the current to the base of transistor 1140 is no longer supplied, so this transistor 114 is turned off, and the current that was being supplied to the collector of transistor 106 flows to the base of transistor 1150.
15 is turned on.

As a result, capacitor 18 is shorted and rapidly discharges.

Then, the charge in the capacitor 18 is completely discharged,
When the charging voltage reaches Ov, the transistor 107 is turned off, so the output circuit becomes inactive, and the transistor 15 is turned off, cutting off the excessive current.

At this time, the transistor 31 is turned off, and since the transistor 113 is also turned off, the state is the same as the state at the time when charging of the capacitor 18 explained at the beginning is started.

This is the same state as when the timer circuit 25 starts its timer operation.

Therefore, the output circuit 26 is maintained in a non-operating state for a certain time period determined by the timer circuit 25, and the transistor 15 is turned off during this period to cut off excessive current.

If the object is still approaching the detection coil 12 when this timer time has elapsed, the transistor 15 is turned on again and the above operation is repeated, but the time during which the transistor 15 is turned off is The time is determined by the timer circuit 25 and is relatively long, so the average power consumed by the transistor 15 is extremely small.

Therefore, the heat generation (loss) in the transistor 15 is small, and an output transistor with a small wattage can be used.

Note that the dotted line indicates the case where the PNP transistor 150 is connected, and in this case, a load such as a relay is connected between the output terminal and the negative power supply line.

In this case, the current detection resistor 16a is the transistor 1
This resistor 16 is connected between the emitter of 5 and the positive power supply terminal.
When the voltage across a increases, transistor 32 is turned on, transistor 33 is turned on, and the base potential of transistor 108 is set to Ov.

That is, in the case of the circuit shown by this dotted line, when an object approaches the detection coil 12, the transistors 133, 13
5 is off and transistors 134 and 136 are on, the output transistor 15a is turned on and the current of the output signal is supplied to the load.

When the detection coil 12 detects an object, transistors 133 and 135 are turned on, and transistors 134 and 1 are turned on.
Since the transistor 36 is off, the transistor 15a is off, and the supply of output signal current to the load is stopped.

When this IC circuit 21 is constructed in a bipolar monolithic manner, there is a parasitic capacitance CB between the point P (common base of transistors 133 and 134) and the ground line as shown by the dotted line.
It is inevitable that this will occur.

The presence of this parasitic capacitance CB slows down the response speed for turning off the output transistor 15 or 15a in the event of an overcurrent, which increases the loss of the transistor 15, 15a. This is a problem when .44 is not connected.

In the present invention, this problem is solved by connecting these as described below).

Assuming that diodes 41 and 43 and resistors 42 and 44 are not connected, when an excessive current flows through transistor 15 and transistor 31 is turned on, transistors 133 and 135 are turned on and transistor 134 is turned on.
, 136 are off, the potential at point P is the power supply voltage VCC.
It rises to a potential of 1 in the near future, and therefore the parasitic capacitance cB is charged with this potential of 1.

Then, by turning on the transistor 31, the output circuit 26 becomes inactive, and the transistors 133 to 1
All 36 try to turn off at the same time, but the parasitic capacitance cB
The charges stored in the transistor 1330 will flow into the base of the transistor 1330 and will flow through the output terminal of the IC circuit 21.

Therefore, when the impedance of the IC circuit 21 when looking outward from the output terminal is large, the discharge time constant becomes large, and the time for turning off the transistor 15 is delayed accordingly.

In addition, when connecting the PNP type transistor 15a shown by the dotted line, the transistor 1 is connected with the transistors 133 and 135 off and the transistors 134 and 136 on.
5a is on, and if an excessive current flows at this time, transistors 133 to 136 try to turn off at the same time.

However, at this time, the potential at point P is approximately O■, and the parasitic capacitance cB is in an uncharged state, so the IC circuit 2
A charging current flows from the output terminal of the transistor 134 into the parasitic capacitance CB through the PN junction between the emitter and base of the transistor 134.

Since this current becomes the base current of the transistor 134, the transistor 15a is not completely turned off while the above-mentioned current is flowing.

This response delay time becomes longer because the larger the impedance of the circuit connected between the output terminal of the IC circuit 21 and the power supply VCC line, the larger the charging time constant of the parasitic capacitance cB becomes.

In this way, if the diodes 41, 43 and the resistors 42 and 44 are not connected, the response time for turning off the output transistor 15, 15a becomes longer due to the parasitic capacitance cB, and the loss of the output transistor increases accordingly. It turns out.

However, in this invention, as described above, the diode 41
゜Because the series circuit of the resistor 42 and the series circuit of the diode 43 and resistor 44 are connected, a part of the discharge voltage of the parasitic capacitance CB is not distributed between the base and emitter of the transistor 133 but to the series circuit of the diode 41 and the resistor 42. Bypassed.

Therefore, the current flowing into the base of the transistor 133 is reduced, the base current of the transistor 1350 is reduced, the fall of the output terminal of the IC circuit 21 becomes faster, and the response time for turning off the transistor 15 becomes faster.

Also, part of the charging current to the parasitic capacitance cB is transferred to the transistor 1.
Since the series circuit of resistor 44 and diode 43 is bypassed instead of between the emitter and base of transistor 13,
40 base current is reduced, and the response time for turning off transistor 15a is shortened.

Series circuit of diode 41 and resistor 42 and diode 4
3. The series circuit of the resistor 44 speeds up the response speed as described above, but by making the value of the resistors 42 and 44 small, it does not interfere with normal operation.

In other words, even if the current supplied from the collector of the transistor 127 is not increased, the transistors 133, 13
4 can be sufficiently driven, and normal operation can be performed without any problems.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional example, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. 1.2...Proximity switch, 10,21...
...IC circuit, 12...Detection coil, 15.1
5a... Output transistor, 16, 16a...
...Resistor for current detection, 18...Capacitor for timer circuit, 19...Shirt capacitor, 22
...Detection circuit, 23... Constant voltage circuit,
24... Current detection circuit, 25... Timer circuit, 26... Output circuit.

Claims (1)

[Claims] 1. An oscillation circuit formed including an externally attached detection coil, a signal processing circuit that generates an output signal according to the oscillation width of this oscillation circuit, and an output circuit such as a transistor,
The charging voltage of the capacitor, which starts charging after the power is turned on, is compared with the reference voltage, and after the power is turned on, a timer operation is performed for a certain period of time to chrome-up the IC. In the proximity switch, the IC circuit is made up of an IC circuit that is converted into an IC circuit, and an output transistor that is externally connected to the IC circuit. The IC is characterized by comprising a transistor that discharges a capacitor of the circuit and puts the output circuit in an inhibited state, and a series circuit consisting of a diode and a resistor connected between the base of the output circuit transistor and the output terminal of the IC circuit. Proximity switch.