JPS63287398A - Electronic wristwatch - Google Patents

Abstract

PURPOSE:To detect the rotation of a stepping motor through a simple and low-priced detection circuit by discriminating the rotation of a rotor through detecting the back electromotive force of a coil. CONSTITUTION:Because no signal is generated in an exciting coil L when a rotor revolves, an electric current decided by a voltage VGS between a resistor R1 and the gate source of a transistor N1 flows also through a transistor N2. Therefore, when there is no signal in said coil L, the input of an inverter I is a high-level one, and its output a low-level one. When the rotor does not revolve and a voltage generated by the back electromotive force of said coil L is applied to the gate of said transistor N2 via a switch S2, the electric current of said transistor N2 increases and takes in all the electric current flowing through a transistor P2 and the output of said inverter I becomes a high-level one. Said high-level output of the inverter I allows detection of no rotation of the rotor of a stepping motor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electronic wristwatch, and more particularly to an electronic wristwatch improved to be able to detect whether or not a step motor is rotating.

[Conventional technology]

Conventionally, detection circuits using operational amplifiers and comparators have been considered as this type of technology, but none have been put to practical use in terms of low voltage operation of 1.1 to 1.

[Problem that the invention seeks to solve]

- Conventional electronic wristwatches were driven with constant pulses regardless of changes in the step motor load or battery voltage, so there was some leeway in the drive pulse width. However, as watches have become thinner in recent years, batteries have become thinner, making it difficult to obtain sufficient battery capacity. For this reason, it is necessary to reduce the current consumption of the motor drive LSI in order to maintain a specified lifespan. It must be reduced to L. For this reason, if the rotor is driven with the lowest power in normal times and is driven with a higher power than usual when the rotor is not rotating, such as when there is no load, rotation can be maintained efficiently with the least amount of current. However, when the battery voltage is 1.5 to 1. Conventionally, it has not been possible to realize a means for detecting the rotation of a motor using a voltage as low as I]V.

[Means for solving the gap and illumination problem: 1 The electronic wristwatch of the present invention includes a first transistor whose source is connected to one terminal of a power supply and supplies a constant current, and a transistor with a conductivity different from that of the first transistor. a second transistor whose drains are connected to each other and whose source is connected to the other terminal of the power supply; and one end is connected to the gate of the second transistor via the first switch. and has a coil of a step motor connected to a reference voltage at the other end via a second switch.

〔Example] Next, the present invention will be explained with reference to the drawings.

FIG. 4 shows a drive circuit for an excitation coil of a general step motor. The output of the first drive inverter composed of P-channel transistor P4 and N-channel transistor N4 becomes high level, and P-channel transistors P3. A second transistor consisting of an N-channel transistor N3
When the output of the drive inverter becomes low level, current flows through the excitation coil, making it possible to rotate the rotor of the step motor by half a rotation. Further, when the output of the second drive inverter becomes high level and the output of the first drive inverter becomes low level, a current flows in the opposite direction to the excitation coil and the rotor of the step motor rotates another half rotation.

FIG. 1 shows a detection circuit according to an embodiment of the present invention. This circuit attempts to detect the rotation of the step motor by detecting the voltage generated in the excitation coil of the step motor. When current flows through the excitation coil of a step motor and the rotor attempts to rotate, the current is too small to rotate, and when the rotor returns to its original position, a back electromotive force is generated in the coil. In this embodiment, the rotation of the rotor of the step motor is determined by detecting the voltage generated at this time. After the drive circuit shown in FIG. 4 finishes supplying current to the step motor, the switch S1. At S2, the connection between both ends of the coil is switched to the detection circuit shown in FIG. The transistor N1 is an N-channel type MOS transistor connected in series with the resistor R1 to generate a reference voltage and supply it to one end of the coil L. Further, the other end of the coil is connected to the gate of the transistor N2 via the switch S2. A resistor R2 is connected to the gate-drain connection point of the transistor P, and the gate of the transistor P2 is connected to the gate of the transistor P to form a current mirror. A constant voltage determined by the gate-source voltage Vgg of transistor P flows.

When no signal is generated in the coil, the transistor N,
Since N also constitutes a current mirror, a current determined by resistor R1 and V145 of transistor N1 also flows through transistor N2. Does the current flow through transistor N2 rather than the current flowing through transistor P2? If R and R2 are set so that ttj is smaller, the input of the inverter I is at a high level when there is no signal across the coil, so the output is at a low level.

When the voltage generated by the back electromotive force of the aforementioned coil is applied to the gate of the transistor N2 via the switch S2, the current of the transistor N2 increases, and the current of the transistor P2 increases.
When all the current flowing through is drawn in, the input of inverter ① becomes low level and the output 0 becomes high level. The high level output of this inverter allows it to be detected that the rotor of the step motor has not rotated.

In the circuit shown in Figure 1, the stacking of elements connected in series between power supplies, such as resistors and transistors or transistors and transistors, is extremely simple, so the influence of the transistor threshold can be greatly reduced, and the power supply Even a low voltage device such as a battery can be operated at a voltage as low as 1.1V to 1.5V.

FIG. 2 is a circuit diagram of another embodiment of the present invention.

In the figure, parts having the same function as in FIG. 1 are given the same reference numerals. In this embodiment, the polarities of the P-channel transistor and N-channel transistor are reversed from those in FIG. 1, and a switch S3 is added. Since switch 3 is used for watches, it is necessary to save current, so the current of the rotation detection circuit must be reduced as much as possible, so switch 3 is closed within a set time to detect the rotation of the step motor. It is something.

FIG. 3 shows still another embodiment of the present invention, in which an N-channel transistor N5 is provided in place of the resistor R2 in FIG. 1, and a current mirror circuit (N1+N5. By adding a current ratio and a threshold to P1.P2), it is possible to keep output 0 at a low level when no signal is generated in the coil.

〔Effect of the invention〕

As explained above, according to the circuit of the present invention, it is possible to realize an electronic wristwatch having a step motor detection circuit, which operates at an extremely low voltage, has a simple configuration, and is inexpensive.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of one embodiment of the present invention, Fig. 2 is a circuit diagram of another embodiment of the invention, Fig. 3 is a circuit diagram of still another embodiment of the invention, and Fig. 4 is a general circuit diagram. FIG. 2 is a circuit diagram of a drive circuit included in the electronic wristwatch. R,, R2...Resistance, L...Exciting coil, N,,N
2~N5...N channel transistor, p,, p2
~P4...P channel transistor, S l , S
2 + S 3...Switch, ■...Inverter, O...Output terminal, 1st generation, St Fig. 2 f4 Fig.

Claims (1)

[Claims] a first transistor whose source is connected to one terminal of the power supply and supplies a constant current; and a drain of the first transistor whose source is connected to the other terminal of the power supply; and a step motor having one end connected to the gate of the second transistor via a first switch and the other end connected to a reference voltage via a second switch. An electronic wristwatch characterized by having a coil.