JP2982416B2 - Speed detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotation speed detecting circuit using a reed switch.

[0002]

2. Description of the Related Art Conventionally, as a vehicle speed meter for detecting a vehicle speed, rotation speed detection using a reed switch 2 as shown in FIG. 8 has been performed. In addition to the vehicle speed meter, the load current i _in flowing through the reed switch 2 is increasing with an increase in various control circuit loads such as engine control, automatic transmission control, and automatic door lock control. Such, in order to respond to increased load on the reed switch 2, the transistor T _r1 as shown in FIG. 9, but corresponding also been started taken to provide a current amplification circuit due to transistors T _r2, to both ends of the reed switch 2 input voltage V _in applied Te of large fault of the reed switch is large, it requires reduction of the input voltage V _in order to increase the reliability.

That is, in the conventional circuit of FIG. 9, when the reed switch 2 is turned off, a high input voltage according to the following equation (1) is applied to the reed switch 2. _{V in ~ R 2 V B /} (R 1 + R 2) ... (1) Thus, conventionally an on reed switch 2 as shown in FIG. 10, by the repetition of off across a high input voltage is intermittently of the reed switch Had been added.

[0004]

The problem to be solved by the present invention is to realize a current amplifying circuit which aims to reduce the input voltage applied to both ends of the reed switch at the same time as the current amplification in the rotational speed detecting circuit. It is in.

[0005]

SUMMARY OF THE INVENTION The present invention provides a reed switch which is interrupted by a rotating magnet, and a reed switch for the reed switch.
And a current amplifying circuit for amplifying a current corresponding to the intermittent,
In a rotation speed detecting circuit having an amplifying semiconductor device at an input stage of the current amplifying circuit , a polarity from the input to the output between an input of the reed switch and an output of the amplifying semiconductor device. And a one-way semiconductor element is provided. According to the above configuration, when the amplifying semiconductor device in the input stage is turned on, the input voltage between the input section of the reed switch and the ground decreases to substantially the forward voltage of the one-way semiconductor element. Therefore, a current amplifier circuit that can solve the above-described problem with a simple circuit configuration has been realized.

[0006]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.
R ₁ , R ₂ , R ₃ denote resistors, D ₁ diodes, Tr ₁ , Tr ₂ denote transistors, 1 denotes a rotating magnet rotor, and 2 denotes a reed switch. Feature for the prior art circuit is that of providing the diode D ₁ between the collector of the inverting amplifier Doranjisuta Tr ₁ of the input stage and the input signal terminals of the reed switch 2. The first embodiment (FIG. 1) is used when it is necessary to keep the input voltage applied to the reed switch 2 as low as possible.

The operation of the first embodiment is as follows. When reed switch 2 is closed by the rotor 1 (when on) are input to and the switch an input voltage V _in across the reed switch 2 is zero (= 0) from the power supply V _B the following formula (2) Electric current flows. i _in = V _B / R ₁ (2) In the first embodiment, the operating current of the reed switch 2 is 2 mA.
10 kΩ is used for the resistor R ₁ to make the following. Therefore, the input current i _in is given by i _in = 12 (V) / 10 (KΩ) = 1.2 (mA) from the equation (2). At this time, since the base of the transistor T _r1 of the input stage no current flows, the collector current of the transistor T _r1 is cut off, the following current flows to the base of the transistor T _r2. i _B2 = V _B / R ₃ = 12 (V) / 10 (KΩ) = 1 · 2 (mA) The collector current of the transistor _Tr2 can draw a current corresponding to the current amplification (h _FE ). Become.
For example, when h _FE min = 100, the output current capability is −12.
0 (mA).

[0008] Then, when the reed switch 2 is turned off, base current flows from the power source V _B through a resistor R _1, R ₂ in the transistor T _r1. Potential of the divided input voltage V _in by the resistor R ₁ and R ₂ are as follows. The collector current I _C1 of the transistor T _r1 by the base current
Flow, this time as long as the extent permitted by the current amplification factor h _FE of the transistor T _r1 is the following relationship (3) is satisfied. V _in = V _D1 + V _CE1 (3) Here, if the collector potential V _CE1 is sufficiently on with respect to the base current, V _CE1 becomes 0 (V) (3).
Input voltage V _in the equation is the following value. V _in to V _D1 = 0.6 (V)

Accordingly, the time of reed switch-on and off the input voltage V _in is between zero (0) and V _D1 ~ 0.6 (V) (Figure 2). Irrespective of the ON / OFF state of the reed switch 2, the operating current of the reed switch and the potential difference (input voltage) at both ends can be kept low, and the input voltage during the operation of the reed switch is reduced
Reliability can be improved.

FIG. 3 shows a reed switch 2 as a second embodiment.
Of showing an example of adding two diodes D ₁ and D ₂ between the collectors of the input terminal and the input stage transistor T _r1. The basic operation of the second embodiment is the same as that of the first embodiment (FIG. 1). However,
In the example of FIG. 1 with respect to should I use a larger current amplification factor h _FE as the input stage transistor T _r1, the second
In the embodiment, the current amplification may be small. That is, FIG.
In the circuit configuration of the reed switch 2 is the input voltage V _in when the off-state by the following equation (4). V _in = V _D1 + V _D2 + V _CE1 to 2 V _D1 = 1.2 (V) (4) where V _D1 is a forward voltage of the diode D ₁ ,
_D2 both forward voltage a forward voltage of the diode D ₂ are substantially equal. Therefore, the input voltage of the transistor T _r1 is,
Since it increased by the forward voltage of the added diode D _2, that the base current of the transistor T _r1 becomes large, selected lower than the current amplification factor of the transistor T _r1 in the circuit (Fig. 1) of the first embodiment Becomes possible. However, in comparison with the first embodiment, the input voltage V _in of the reed switch of the reed switch 2 is in the off state about 1.2 (V)
And one diode (FIG. 4). The second embodiment (FIG. 3) is an embodiment in which the input voltage applied to the reed switch may be increased more than the first embodiment. Although two diodes are used in FIG. 3, the same effect can be obtained by using three or more diodes.

[0011] The third embodiment is a combination example of the Zener diode ZD and a diode D ₁ (FIG. 5). As the Zener diode ZD, a low voltage (for example, 2.4 to 3.0) is used.
V) type is used. In the above configuration, the input voltage V _in by the following equation (5) is a reed switch 2 is turned off is applied to both ends of the reed switch 2. _{V in = V ZD + V D1} + V CE1 ... (5) where, V _ZD is a Zener voltage, V _D1 is a diode forward voltage, V _CE1 transistor T _r1 is the collector of the ON state, the emitter voltage is there. In equation (5), V _ZD = 2.4 (V), V _D1 = 0.6 (V), V _CE
= 0 on the (V), become V _in = 3 (V). That is, the input voltage V _{in is} equivalent to the addition of the zener diode ZD.
There order also increases the base current of the increased transistor T _r1, it is possible to configure the circuit by further current amplification factor h _FE lower transistor than the second embodiment (FIG. 3). FIG. 5 shows an embodiment in which the input voltage applied to the reed switch may be slightly increased.

The fourth embodiment is an example in which an inverting amplifier of an operational amplifier OP is used as an amplifying semiconductor device (FIG. 6). In Figure 6, we have added two diodes D ₁ and D ₃ between the output of the input section of the reed switch 2 and the former-stage operation amplifier OP. The basic operation of the fourth embodiment is the same as that of the second embodiment (FIG. 3). That is, the input voltage V _in the reed switch 2 is turned on it is zero. When reed switch 2 is turned off, the input voltage V _in increases, operational when amplifier input voltage V _in the reference voltage V ₁ of the OP exceeds, the output voltage V ₂ the operational amplifier is inverted to the ON state is zero the cathode of the diode D ₃ is grounded, an input voltage V _in of the reed switch 2 becomes the following equation. V _in = V _D2 + V _D3 = 2V _D = 1.2 (V) (6) The operation of the fourth embodiment is as shown in FIG.

[0013]

As described above, when the amplifying semiconductor device of the input stage is turned on, the input voltage between the input portion of the reed switch and the ground is substantially equal to that of the one-way semiconductor element. Since the voltage is reduced to the forward voltage, the input voltage applied to both ends of the reed switch can be suppressed at the same time as the current amplification, and there are excellent effects such as a simple circuit configuration.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a rotation speed detection circuit according to a first embodiment.

FIG. 2 is a time chart showing the operation of the first embodiment.

FIG. 3 is a circuit diagram illustrating a rotation speed detection circuit according to a second embodiment.

FIG. 4 is a time chart showing the operation of the second embodiment.

FIG. 5 is a circuit diagram illustrating a rotation speed detection circuit according to a third embodiment.

FIG. 6 is a circuit diagram illustrating a rotation speed detection circuit according to a fourth embodiment.

FIG. 7 is a time chart showing the operation of the fourth embodiment.

FIG. 8 is a circuit diagram showing a conventional technique.

FIG. 9 is a circuit diagram of a rotation speed detection circuit provided with a conventional current amplification circuit not according to the present invention.

FIG. 10 is a time chart showing the operation of the conventional rotation speed detection circuit shown in FIG.

[Explanation of symbols]

1 ... rotor, 2 ... reed switch, V _in ... input voltage, i _in ... input current, R ₁ to R ₆ ... resistor,
_{D 1, D 2, D 3} ... diodes, T _r1, T _r2 ... transistors, V _B ... supply voltage, V _OUT ... output voltage, G
ND ... ground, the forward voltage drop of V _D ... Diode,
ZD: Zener diode, OP: Operational amplifier

Claims (1)

(57) [Claims] 1. An amplifying semiconductor device is provided at an input stage of the current amplifier circuit , comprising: a reed switch that is turned on and off by a rotating magnet; and a current amplifier circuit that amplifies a current corresponding to the on / off state of the reed switch. A rotation direction detection circuit comprising: a one-way semiconductor element provided between the input part of the reed switch and the output part of the amplifying semiconductor device with a polarity from the input part to the output part. Rotation speed detection circuit.