JPS6326896B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit suitable for integrating a high frequency oscillation type proximity switch into an IC that detects the presence or position of an object without contact.

A conventional high-frequency oscillation type proximity switch integrated into an IC circuit is constructed as shown by a two-dot chain line 1 in FIG. That is, it has positive and negative power supply terminals 11 and 12, an output terminal 13, a coil terminal 14, and a constant voltage terminal 15 as terminals for connection with the outside, and inside thereof there are an oscillation circuit 16, a comparator 17, an integration circuit 18, and a comparator. 19, an output circuit 20, a power reset circuit (a circuit for preventing erroneous output from the output circuit 20 when the power is turned on) 21, and a constant voltage circuit 22 are formed. Note that the external connection terminals include a variable resistor terminal for operating distance adjustment, an integrating capacitor terminal, a power supply reset capacitor terminal, etc., but these are omitted from the explanation in this specification. A detection coil 2 and a capacitor 3 are connected between the coil terminal 14 and the negative power terminal 12, and a bypass capacitor 4 is connected between the constant voltage terminal 15 and the negative power terminal 12. It's starting to connect. When an object such as a metal approaches the detection coil 2, the oscillation width of the oscillation circuit 16 changes, and this is changed by the comparator 17, the integration circuit 18,
It is detected by a comparator 19 and an output signal is generated by an output circuit 20.

By the way, a circuit configuration as shown in FIG. 2 has been proposed for this constant voltage circuit 22. Note that in FIG. 2, the circuits other than the constant voltage circuit are expressed as a load 61. Transistors 31 and 32 constitute a current mirror circuit, and transistor 33 functions as a main control transistor of a series-controlled voltage stabilizing circuit. The Zener diode 51 functions as a constant voltage element, and the transistor 34 is for temperature compensation of the Zener diode 51.

In this circuit of Fig. 2, I ₁ R ₁ +V _BE1 = V _BE2 I ₁ R ₁ = V _BE2 −V _BE1 = △V _BE = V _Tlo (I ₀ + I ₂ /I ₁ ) I ₁ = V _T /R ₁ ×ln (I ₀ + I ₂ / I ₁ ) V _T = KT / q = thermal voltage (I ₀ ; current flowing into the collector of the transistor 33, I ₁ ; current flowing into the collector of the transistor 31, I ₂ ; flowing into the resistor 42 The relationship holds true: current, R ₁ ; value of resistor 41, V _BE1 ; base-emitter voltage of transistor 31, V _BE2 ; base-emitter voltage of transistor 32). i.e. current I ₀ and I ₂ and current I ₁
maintains a constant relationship at a ratio determined by the value R ₁ of the resistor 41.

When the power supply voltage Vcc is sufficiently higher than the Zener voltage Vz of the Zener diode 51, the transistor 3
Voltage on the emitter side of 3, that is, voltage on the constant voltage output side
Vstab is Vstab = Vz + V _BE4 - V _BE3 (V _BE3 , V _BE4 ; voltage between base and emitter of transistors 33 and 34) If V _BE4 ≒ V _BE3 , Vstab = Vz and maintains an almost constant voltage.

In this case, assuming that the load 61 has a constant impedance, the current I _L flowing into the load 61 is constant, I _L = I ₀ /h _FE3 + I ₀ = 1 + h _FE3 /h _FE3 I ₀ ≒ I ₀ (h _FE3 = transistor 33 h _FE ) holds true. Therefore, the current I ₁ changes by the amount of change in the current I ₂ and becomes I ₀ =I ₀ +I ₂ /n (n: constant of proportionality).

Therefore, in a region where the constant voltage Vstab maintains a constant value, when the power supply voltage _Vcc changes, the current Icc flowing to the terminal 11 is determined by the value _R2 of the resistor 42: _I2 = Vcc - V _BE2 −V _BE3 −Vz/R ₂ The current I ₂ increases or decreases according to the power supply voltage Vcc. This resistor 42 is a resistor for activating the transistor 33 to start flowing the current _I0 when a voltage is applied to the terminal 11, and thereby supplying the current _I1 , and for operating this constant voltage circuit. It is used as a trigger. Therefore this resistance 4
If the value R ₂ of 2 is too small, the current I ₂ will increase as the power supply voltage Vcc increases, as shown in the above equation, and the current consumption of the entire circuit flowing between the power supply terminals 11 and 12 will increase, which is wasteful. It will happen. Therefore, generally the value R ₂ of resistor 42 is set as high resistance,
The value R ₁ of the resistor 41 is determined by driving the transistor 33 with the current I ₂ to cause the current I ₀ to flow, and by causing the current I ₁ to flow, further driving the transistor 33 to generate a predetermined current value I ₀ . The Zener current is determined to flow through the Zener diode 51 such that the Zener voltage is constant and the Zener voltage is constant.

This circuit is the main control transistor 3 of the constant voltage circuit.
The base current of transistor 3 and the zener current flowing through zener diode 51 are limited to the necessary minimum, and a type of current limit is applied to the drive current of transistor 33 to prevent unnecessary current from flowing through zener diode 51. It's on.

However, this circuit has the following drawbacks.
When the power supply voltage Vcc gradually rises, a current _I2 flows through the transistor 32 and the resistor 42, driving the transistor 33. However, at this time, if Vcc is lower than the Zener voltage, the Zener current Iz does not flow I. A current I 0 of ₀ = h _FE3 · _{I 2 flows} into the collector of the transistor 33. As a result, a current flows into the collector of transistor 31.
I ₁ flows, which further increases the current I ₀ . This is repeated and according to the power supply voltage Vcc, Vcc = I ₂ R ₂ + V _BE2 + I ₀ R _L + V _BE3 ... (1) where I _L ≒ I ₀ (I _L ; current flowing through load 61 R _L ; resistance of load 61 value) is maintained and stable. In this case, the following holds true: I ₀ = (I ₁ + I ₂ ) h _FE3 (2) I ₁ = I ₂ + I ₀ /n (3) (n: constant of proportionality). Therefore, the following equation can be obtained from equations (2) and (3) above.

I ₂ = n - h _FE3 / (1 + n) h _FE3 I ₀ ... (4) (i) If n > h _FE3 , from equations (1) and (4), I ₀ = Vcc - (V _BE2 + V _BE3 ) / KR ₂ +R _L However, K=n-h _FE3 / (1+n)h _FE3 Therefore, in this case, the current I ₀ changes linearly according to the power supply voltage Vcc, and the power supply voltage Vcc and the base voltage of the transistor 33 V ₀ and stabilized voltage
The relationship with Vstab is shown in Figure 3.

(ii) In the case of n=h _FE3 , I ₂ = 0 and I ₀ = Vcc-(V _BE2 + V _BE3 )/R _L Therefore, in this case, the current I ₂ initially flows to drive the transistor 33, and the current I ₀ As a result, the voltage V _CB between the collector and base of the transistor 33 becomes V _CB = 0, and the current I ₁ becomes I ₁ = Vcc − V _BE2 − V _BE3 − _{I 0} R _L /R ₁ = V _BE2 − V _BE1 /R ₁ , which means that only the bias current generated by the current mirror circuit formed by the transistors 31 and 32 with the resistor 42 removed operates.

(iii) When n < h _FE3 , I ₂ < 0, and the current I ₂ flows in the opposite direction to the arrow in Figure 2.
That is, the base side of the transistor 33 is biased to a positive potential, and the collector side is biased to a negative potential. This can occur because a diode formed by the transistor 32 is inserted between the collector side of the transistor 33 and the power supply voltage Vcc. In this case, the transistor 33 is in a saturated state, and the voltage between the collector and emitter of the transistor 33 becomes the saturation voltage Vsat, and since Vsat<V _BE3 , V ₂ =Vsat−V _BE3 <0.

As a result, the collector side of the transistor 31 is biased positively and the base side is biased negatively, and the current mirror circuit formed by the transistors 31 and 32 does not operate normally, and the current is approximately determined by the power supply voltage Vcc and the value R ₁ of the resistor 41. A current larger than the current during current mirror operation flows as current _I1 . At this time, if V _BE2 ≒V _BE3 , then Vcc=V _BE2 +V ₂ +V ₀ , so Vcc=V ₀ +Vsat, and I ₁ becomes I ₁ ≒Vsat/R ₁ .

In this case, if the power supply voltage Vcc further increases, when Vcc = Vz + V _BE4 + V _BE2 , the potential difference across the resistor 42 becomes 0, the above-mentioned reverse bias is eliminated, and the current mirror circuit formed by transistors 31 and 32 operates normally. start an action. In this case, n<h _FE3 means that the value R ₁ of the resistor 41 is small, and the current I ₁ in the saturated state and I ₁ in the normal state
As a result, the difference between the two values increases, resulting in a negative characteristic as shown in FIG.

As a result, the characteristics shown in FIGS. 4, 5, and 6 are obtained.

As described above, the operations differ depending on the three relationships between n and _hFE3 . In case (i), the current I ₁ alone is insufficient to cause the load current I _L to flow, and the current I ₂ must be used. In other words, if the value R ₂ of the resistor 42 is high, the resistor 4
Unless the potential difference between both ends of Vstab becomes large and the necessary load current I _L and the current Iz necessary for the Zener diode 51 to maintain a constant voltage flow, the stabilizing voltage Vstab will not be in the constant voltage region. Conversely, if the resistance value R ₂ is made small and the necessary load current I _L and necessary Zener current Iz are started to flow while the potential across the resistor 42 is small, then as the power supply voltage Vcc increases, , the current I ₂ increases and the transistor
The bias current of Q ₃ increases, making it impossible to achieve the original objective of making the bias current constant.
Furthermore, this results in an increase in current consumption due to the current I ₂ , which also affects the power when integrated into an IC (the power consumption is limited by the IC package, making it impossible to increase the output stage drive current).
Also, when this IC circuit is used as the sensor part of an AC 2-wire proximity switch, the current consumption is large, so even when the load, such as a relay, is turned off, a large leakage current will flow through the relay. This is not preferable for light-load relays, etc., as it may cause reset failure or chattering.

In case (iii), a negative phenomenon occurs in the bias current of the transistor 33. For example, if R ₁ = 2KΩ (n≒40), I _L = 2mA h _FE3 = 100, and Vsat = 0.1V, I ₁ = 50μA, I ₂ = 0, and when normal, I ₁ = 20μA, so when moving from saturation to normal, from 50μA
The current will drop to 20μA. Therefore, if an attempt is made to prevent the oscillation waveform from being superimposed on the constant voltage line by connecting the bypass capacitor 4 to the constant voltage terminal 15, an oscillation phenomenon (shown in FIG. 7) due to this negative phenomenon will occur, which is an inconvenience. There is.

This negative phenomenon occurs in the vicinity where the stabilizing voltage Vstab becomes a constant voltage, so although we would like to expand the operating voltage range of the IC to as low as possible to make it easier to use, this limits the operating voltage range. must be limited. Furthermore, when used as an AC two-wire proximity switch, the voltage that remains when the load is turned off, that is, the residual voltage, increases, which is undesirable. In any case, the existence of a region in which an oscillation phenomenon occurs in a constant voltage circuit is undesirable from a circuit standpoint.

In addition, case (ii) is the most desirable state. That is, if the transistor 33 is first triggered by the current I ₂ , the voltage V _CB between the collector and base of the transistor 33 becomes V _CB = 0, the current I ₂ does not flow, and it remains constant even if the power supply voltage Vcc changes. In the voltage domain, if the resistance R _L of the load 61 is constant, the current consumption does not change at all.

However, h _FE3 varies greatly depending on temperature, and n
It also changes with temperature, so it is practically impossible to set n=h _FE3 over the entire temperature range (usage temperature).
Even if you set n=h _FE3 at room temperature, if the temperature changes, it will slide to case (i) or (iii).

In view of the above, the present invention provides main control transistor 33
The bias current of the circuit is configured so that it hardly changes even with large changes in the power supply voltage Vcc, thereby suppressing the increase in current consumption and creating a stable bypass capacitor that does not cause negative phenomena. It is an object of the present invention to provide a circuit of a proximity switch with an attached constant voltage circuit.

An embodiment of the present invention will be described below with reference to FIG. In FIG. 8, transistor 73 serves as the main control transistor of the series-controlled stabilizing circuit. A Zener diode 8 is connected to the base of this transistor 73 to make the base voltage constant.
4 are connected. Note that the diode 83 is for temperature compensation of this Zener diode 84. A resistor 81 is connected between the collector and base of the transistor 73.
is connected. Transistors 74 and 75 constitute a current mirror circuit. transistor 7
1 and 72 also constitute a current mirror circuit.

In the circuit shown in FIG. 8, when the power supply voltage Vcc gradually rises, a current I _R flows through the resistor 81 and drives the transistor 73. At this time, if the power supply voltage Vcc is lower than the zener voltage, the zener current Iz does not flow and a current I ₀ of I ₀ =h _FE3 ·I _R flows out from the emitter. This current I ₀
Since the current I _L flows through the load 61 and the current I flows through the resistor 82, I ₀ =I+ _IL . When this current I flows, transistor 7
A current I ₁ flows through the collector of the transistor 74 through the current mirror circuit formed by the transistor 74 . this current
I ₁ causes current I ₂ to flow through the collector of transistor 72 by a current mirror circuit made up of transistors 71 and 72 . In FIG. 8, the configuration is such that I≒I ₁ ≒I ₂ . However, I ₁ =I/m and I ₂ =I ₁ /n (m, n: constant of proportionality) may be configured so that I ₂ =I/mn.

The following relationship holds true with this I ₂ : I ₀ =(I ₂ +I _R )h _FE3 This current I ₀ is divided into a current I and a current I _L , and is fed back again, so that I ₀ increases again. In this way, the current I ₀ increases and becomes stable when the stabilized voltage Vstab reaches a predetermined value depending on the power supply voltage Vcc.

Here, even if transistor 73 is saturated, the collector of transistor 73 is at the power supply voltage.
Since it is connected to Vcc and there is no diode in between as shown in FIG. 2, the collector side of the transistor 73 is always positive and the base side is negative, and the transistor 72 is never saturated. Therefore, transistors 71 and 72 always function as a normal current mirror circuit.

That is, the collector-emitter voltage V _CE of the transistor 73 is V _CE =V _BE3 +I _R R ₁ (R ₁ ; value of the resistor 81).

In this way, since no negative phenomenon occurs in the current I ₂ ,
A bypass capacitor for preventing superimposition of oscillation waveforms can be attached to the constant voltage terminal 15 without any worries.

Also, if I ₂ > I ₀ /h _FE3 , the current Iz will be Iz = I _R + I ₂ - I ₀ /h _FE3 , and even if the current I _R is a small enough value to be used only for the first trigger, A current Iz of Iz≒I ₂ −I ₀ /h _FE flows through the Zener diode 84, and the base voltage of the transistor 73
V ₀ maintains a sufficiently constant voltage. Therefore, the value R ₁ of resistor 81 only needs to be large enough to drive transistor 73 initially.

Furthermore, in the case of Vcc > V _D + Vz + V _EC (V _EC ; voltage between the emitter and collector of transistor 72), once the current I _R causes transistor 73 to
Once driven, the stabilizing voltage Vstab remains constant even if the resistor 81 is removed, and even if the power supply voltage Vcc changes, the current Icc flowing between the terminals 11 and 12 does not change and remains constant.

Also, even if resistor 81 is connected, resistor 8
1 can be a sufficiently large high resistance, so the power supply voltage Vcc
The change in the current I _R is also small with respect to the change in , and as a result, the change in the current Icc is also small, and there is almost no change in the current consumption.

As described above, according to the present invention, in a proximity switch circuit having a bypass capacitor that prevents the oscillation waveform from being superimposed on the power supply line, a high resistance is connected between the input side and the base of the main control transistor. A first circuit that positively feeds back a portion of the output of the control transistor as a reference current to the base of the main control transistor;
Since the second current mirror circuit is provided, the voltage at the base of the main control transistor quickly becomes a constant voltage due to positive feedback, and only the current flowing through the high resistance changes due to changes in the power supply voltage. Since the resistance value is high, the current that flows is small, so there is almost no change in the current consumption, and the current consumption itself can be made small. In addition, the value of the power supply voltage in the constant voltage region is sufficient as long as it is equal to or higher than the voltage generated between the constant voltage elements plus the ON voltage of the transistor that constitutes the second current mirror circuit, which limits the range of power supply voltage that can be used. It can be taken widely.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional example, FIG. 2 is a circuit diagram specifically showing a part of FIG. 1, FIGS. 3 and 4 are graphs showing each voltage characteristic of FIG. 2, and FIG. The figure is a graph showing the relationship between power supply voltage Vcc and current _I1 in Figure 2, Figure 6 is a graph showing the relationship between power supply voltage Vcc and Zener current Iz, and Figure 7 is a graph showing the relationship between power supply voltage Vcc and current Iz in Figure 2.
A graph showing the relationship between Vcc and stabilization voltage Vstab,
FIG. 8 is a circuit diagram showing one embodiment of the present invention. 16...Oscillation circuit, 17, 19...Comparator, 18...Integrator circuit, 20...Output circuit, 21
... Power supply reset circuit, 22 ... Constant voltage circuit, 3
3, 37... Main control transistor of series control type stabilization circuit, 31; 32, 71; 72, 74; 7
5....A transistor that constitutes a current mirror circuit.

Claims (1)

[Claims] 1. An oscillation circuit formed including a detection coil;
It has a signal processing circuit that generates an output signal according to the oscillation amplitude of this oscillation circuit, a constant voltage circuit that applies a constant voltage to these circuits, and a bypass capacitor that prevents the oscillation waveform from being superimposed on the power supply line. In the proximity switch circuit, the constant voltage circuit is connected between a series-controlled main control transistor having a constant voltage element connected to its base, and the input side of this main control transistor and the base, and when the power is turned on, this main control circuit is connected. a high resistance that allows a current sufficient to operate the transistor to flow through the base; a first current mirror circuit that uses a portion of the current flowing to the output side of the main control transistor as a reference current; and the first current mirror circuit. A proximity switch circuit comprising a second current mirror circuit for flowing a current between the input side and the base of the main control transistor using the current as a reference current.