JP3371067B2 - Noise suppression circuit for automobile clock - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a noise countermeasure circuit for an automobile timepiece which prevents deterioration of display quality due to intrusion of noise. 2. Description of the Related Art As shown in FIG. 2, a conventional automobile timepiece comprises a timepiece circuit 2, a constant voltage circuit 4, and a smoothing circuit 6. The clock circuit 2 includes an IC 10 to which a quartz oscillator 8 is connected and which measures time.
Display unit 1 for displaying the time based on the drive signal from
And 2. The constant voltage circuit 4 is composed of a resistor R1 connected in series to a power supply 14 such as an automobile battery, and a Zener diode Z1 connected in parallel to an output terminal. Further, the smoothing circuit 6 is composed of a capacitor C connected in parallel to the output terminal, and acts to remove the pulsation component of the output of the constant voltage circuit 4. In the above-mentioned conventional automobile timepiece, a power source 1
The constant voltage circuit 4 converts the output voltage of No. 4 into a stable voltage of a predetermined value and supplies it to the IC 10. In order to drive this automobile watch, a current (I1 + I2) composed of a current I1 supplied to the IC 10 and a current I2 flowing through the Zener diode Z1 is required, and this current (I1 + I2) is set by the resistor R1. It was. [0004] In the above-mentioned conventional automobile timepiece, noises such as radio waves of radio equipment and high frequency noise are generated.
When radiated into the (+) side of the power supply 14 and enters, the internal impedance of the Zener diode Z1 is reduced by this noise, and a current larger than the normal current I2 flows into the Zener diode Z1. As the current I2 increases in this manner, the voltage drop across the resistor R1 increases, the output voltage applied to the IC 10 drops, and the voltage applied to the display unit 12 also drops, resulting in darker display and noise. There is a problem that the display quality during the intrusion is reduced. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the related art, and has as its object to provide an anti-noise circuit for an automobile timepiece which prevents deterioration of display quality due to intrusion of noise. A noise countermeasure circuit for a vehicle timepiece according to the present invention is a vehicle timepiece that supplies power from a power supply to a timepiece circuit through a constant voltage circuit. A voltage drop suppression circuit is provided for supplying a shortage of current to the clock circuit in response to a drop in output voltage due to a voltage drop in the circuit to suppress the voltage drop. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The noise countermeasure circuit for an automobile timepiece according to the present invention detects a drop in the output voltage of the constant voltage circuit due to the intrusion of noise, and supplies an insufficient current to supply a voltage drop. And a voltage drop suppressing circuit for suppressing the voltage drop. This voltage drop suppressing circuit has a Zener diode Z2 connected in parallel with a resistor R1 in a constant voltage circuit for setting a current necessary for driving a clock circuit. When the internal impedance of the Zener diode Z1 connected to the output side of the resistor R1 decreases due to noise and the voltage drop in the resistor R1 increases, a Zener current flows through the Zener diode Z2 due to the potential difference at that time, and this current is By supplying the clock circuit, the shortage of the current is compensated and the voltage drop is suppressed. FIG. 1 is a circuit diagram showing a configuration of an anti-noise circuit of an automobile timepiece according to an embodiment of the present invention. The basic structure of the vehicle timepiece is the same as that of the conventional vehicle timepiece shown in FIG. 2, and the same reference numerals are given. In the vehicle timepiece of this embodiment, a voltage drop suppression circuit 16 is connected in parallel with the resistor R1 of the constant voltage circuit 4 as a measure against noise. This voltage drop suppression circuit 16
Is a resistor R2 and a Zener diode Z connected in series.
And 2. The resistance value of the resistor R1 in this embodiment is set by a current (I1 + I2) composed of a current I1 supplied to the IC 10 and a current I2 flowing into the Zener diode Z1, which is a normal current consumption. The Zener diode Z2 has its Zener voltage set so that it does not conduct due to the potential difference between the connection terminals of the resistor R1 in a normal state, and the current I3 passing through the Zener diode Z2 does not flow in a normal state. I have. In the automobile timepiece having the above-described configuration, in a normal state where no noise enters, a current (I1 + I2) determined by the resistor R1 flows, and a voltage maintained at a constant value by the Zener diode Z1 is the IC10.
Is applied to In this state, if radio wave or other high-frequency noise from a wireless device or the like enters the (+) side, the internal impedance of the Zener diode Z1 decreases, and the value of the current I2 flowing in increases. As described above, the voltage drop at the resistor R1 increases by the amount of the increase of the current I2. When the potential difference due to the voltage drop of the resistor R1 becomes equal to or larger than the Zener voltage of the Zener diode Z2, the Zener diode Z2 conducts and the current I3
Flows into the output side and compensates for the shortage of current to suppress the voltage drop. As described above, by suppressing the voltage drop due to the intrusion of noise, the rated current and the voltage are supplied to the IC 10, and the deterioration of the display quality such as the dark display of the display unit 12 is prevented. be able to. When the noise disappears and the internal impedance of the Zener diode Z1 returns to a normal value, the current I
Since the value of 2 also returns to the original state, the Zener diode Z2 does not conduct and the current I3 does not flow due to the potential difference on the output side of the resistor R1. When noise enters, not only the internal impedance of the Zener diode Z2 but also the Zener diode Z1 decreases, but the current I3 also increases with the increase of the current I2. In the operation of compensating for the shortage, the reduction of the internal impedance of the Zener diode Z2 works favorably. Further, since the Zener diode Z2 needs to be in a non-conductive state at normal times, for example, when the Zener voltage of the Zener diode Z1 is set to 5V, a Zener voltage of about 8V higher than that is set. Is set to According to the present invention, by providing the voltage drop suppressing circuit, it is possible to operate in response to the voltage drop of the constant voltage circuit due to the intrusion of noise and to suppress the voltage drop. It is possible to prevent the display quality of the automobile watch from deteriorating due to intrusion of noise.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a configuration of an anti-noise circuit of an automobile timepiece according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing a configuration of a conventional automobile watch. [Description of Signs] 2 Clock circuit 4 Constant voltage circuit 6 Smoothing circuit 10 IC 12 Display unit 14 Power supply 16 Voltage drop suppression circuit R1, R2 Resistance Z1, Z2 Zener diodes I1 to I3 Current

Claims (1)

(57) Claims: 1. A noise countermeasure circuit used for an automobile timepiece that supplies power from a power supply to a timepiece circuit through a constant voltage circuit, wherein the constant value caused by intrusion of noise is provided. automobile clock noise, characterized in <br/> comprise a voltage drop suppression circuit in response to the drop of the output voltage due to a voltage drop in the voltage circuit to prevent the supply to the voltage drop of the shortage of the current to the clock circuit Countermeasure circuit.