JPH0517714U - Constant voltage circuit - Google Patents

Abstract

(57) [Summary] [Purpose] After the power is turned on, no output is generated for a predetermined time.
It is an object of the present invention to provide a constant voltage circuit that prevents malfunctions of instruments and the like due to various noises that occur within a fixed time immediately after power is turned on. [Composition] A comparator 2 is provided in a constant voltage circuit which supplies a voltage supplied from a main power source V _B to a load as a constant voltage V _CC.
The control circuit 1 using is provided. The control circuit 1 keeps the output voltage of the circuit below a minimum voltage value (1 v or less) at which the load can operate for a predetermined time after the main power supply V _B is turned on.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a constant voltage circuit, and more particularly to a constant voltage circuit that keeps an output voltage of a circuit below a voltage value at which a load can operate for a predetermined period after a main power supply is turned on.

[0002]

[Prior Art]

BACKGROUND ART Conventionally, a constant voltage circuit as shown in FIG. 3 is often used as a power source for a drive circuit such as a vehicle speedometer or a tachometer. When the battery voltage V _B is applied to the power supply input terminal, the constant voltage circuit outputs a constant voltage V _c determined by the Zener diode ZD and the transistor TR ₁ . This output voltage is slightly delayed until it reaches a constant voltage V _C due to the value of the capacitor C ₁ connected to the output terminal, but in many cases it is about several msec, and a constant voltage is generated almost at the same time as the application of power. Can be considered.

FIG. 4 shows an example in which the constant voltage circuit is used as a power source for a speedometer drive circuit 20. The speed sensor 10 detects the magnetism of a magnet or the like attached to the rotating portion to generate a pulse. The output of the Hall element 11 generated when the magnetism is detected is amplified by the amplification element 12 to shape the waveform. It is shaped by the circuit 13 and is output from the collector in addition to the base of the transistor TR ₂ .

On the other hand, the drive circuit 20 composed of an IC or the like for receiving the output signal and driving the meter is constructed around an operational amplifier 21, and the power supply of the operational amplifier 21 is the output voltage V _{CC of the} constant voltage circuit. Is being supplied. The output signal of the sensor 10 is input to the negative terminal (reverse input terminal) of the operational amplifier 21 via a low-pass filter (integrating circuit) including a diode D ₁ and R ₂ and C _2. The constant voltage V _{CC of the} output signal is pulled up by the resistor R ₃ . Therefore, when the output TR ₂ of the sensor 10 is on, the input signal pulse is low and is approximately 0 v, and when TR ₂ is off, it is high and approximately Vcc. This signal is configured to drive the meter as a pulse signal after being amplified by an arithmetic circuit having a hysteresis characteristic via the low pass filter.

[0005]

[Problems to be solved by the device]

 However, the capacitor C in the speed sensor 10 is₃Is generally small in capacity because the mounting position of the sensor 10 is in a bad environmental condition and the size required for the sensor 10 itself is small. On the other hand, in the drive circuit 20 without such restrictions, the capacitor C_FourIt is possible to stabilize the circuit by relatively increasing the capacity of. Therefore, if there is a momentary interruption of the power due to noise generated by various electric components or chattering of the ignition key switch, which occurs between several 10 msec and several 100 ms ec immediately after the power is turned on, the TR in the sensor 10 may be interrupted.₂Is turned off because the base current is not supplied, but the constant voltage circuit in the drive circuit 20 has a large capacity C_FourSince it is backed up by, it is not affected by short interruptions. Therefore, as shown in FIG. ₂ ON / OFF of the sensor may appear as an output signal of the sensor 10 as it is, and may be processed by the drive circuit 20 to cause a malfunction, for example, unnecessary meter display.

Chattering of an ignition key switch generally occurs at t = several tens of msec after the switch is turned on. Therefore, a timer circuit is provided in the drive circuit so that an input signal is not received within a certain time after the power is turned on. There may be cases where such measures are taken. However, depending on the vehicle model, t = several hundreds of msec, and it is difficult to increase the number of bits of the counter in the drive circuit 20 with a timer using a crystal oscillator. Can not.

An object of the present invention is to provide a constant voltage circuit which does not generate an output for a predetermined time after power-on and prevents malfunctions of instruments and the like due to various noises generated within a fixed time immediately after power-on. .

[0008]

The present invention is a constant voltage circuit which supplies a voltage supplied from a main power source to a load at a constant voltage, and the circuit is turned on for a predetermined time after the main power source is turned on. It is characterized by a control circuit that keeps the output voltage below the minimum voltage value at which the load can operate.

[0009]

[Action]

 Based on the above configuration, when the main power supply is turned on by a switch or the like and a voltage is applied to the constant voltage circuit, the output voltage of the constant voltage circuit is applied to the load for a predetermined time by the control circuit provided in the constant voltage circuit. The voltage is maintained below the operable voltage value, and a constant voltage is output after a lapse of a predetermined time. For this reason, malfunctions of instruments and the like due to various noises generated within a fixed time immediately after power-on can be prevented.

[0010]

【Example】

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

FIG. 1 shows an embodiment of a constant voltage circuit according to the present invention. The constant voltage circuit is obtained by adding a control circuit 1 to the above-mentioned conventional constant voltage circuit. The control circuit 1 includes a comparator 2, a transistor TR₃, Resistance R_Four,R_Five,R₆, Capacitor C_FiveEtc. The battery voltage V is applied to the non-inverting input terminal (plus input terminal) of the comparator 2._BResistance R_Five, R₆The reference voltage divided by is applied, and the battery voltage is applied to the inverting input terminal (minus input terminal)_FourAnd capacitor C_FiveThe voltage divided by and is applied. The output terminal of the comparator 2 is a transistor TR. ₃ Connected to the base of the transistor TR₃Is the transistor TR of the conventional constant voltage circuit₁Connected to the base of.

When the power source V _B is turned on in this configuration, the reference voltage obtained by dividing the battery voltage V _B by the resistors R ₅ and R ₆ is immediately applied to the non-inverting input terminal of the comparator 2. In contrast, since the terminal voltage of the capacitor C ₅ obtained by dividing the battery voltage V _B by the resistor R ₄ and the capacitor C ₅ to the inverting input terminal is applied, the voltage, as shown in Figure 2, the time Along with this, the voltage gradually rises and finally becomes approximately the battery voltage V _B. Therefore, the terminal voltage of the capacitor C ₅ exceeds the reference voltage V _B × R ₆ / (R ₅ + R ₆ ) of the inverting input terminal T seconds after the power is turned on, and the output of the conoparator 2 becomes T after the power is turned on. It becomes High up to the second, that is, approximately V _B , and becomes Low after 0 seconds and becomes 0 v. Therefore, the transistor TR ₃ remains on for T seconds after the power is turned on, and the constant voltage output becomes a low voltage of less than 1v. After T seconds, the transistor TR ₃ turns off and the constant voltage output becomes the constant voltage Vcc. .. The time T can be arbitrarily set by selecting the values of the capacitor C ₅ and the resistor R ₄ .

When this constant voltage circuit is used as the constant voltage circuit of the drive circuit 20 of the speedometer shown in FIG. 4, even if an output appears in the speed sensor 10 due to chattering of the ignition switch after the power is turned on, the drive circuit is Since the output voltage of the constant voltage circuit 20 is a constant voltage of less than 1v, the drive circuit 20 does not operate, and therefore malfunctions such as unnecessary meter display do not occur. Further, since the time T can be freely set by changing the values of the capacitor C ₅ and the resistor R ₄ , it is possible to meet the specifications of any vehicle type and the like.

[0014]

[Effect of the device]

 As described above, according to the present invention, the control circuit is provided in the constant voltage circuit to keep the output voltage of the circuit below the minimum voltage value at which the load can operate for a predetermined time after the main power is turned on. Therefore, it is possible to prevent malfunction of the load caused by various noises generated immediately after the power is turned on.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a constant voltage circuit according to the present invention.

FIG. 2 is a timing chart showing the relationship between the terminal voltage of a capacitor C ₅ and the output of a comparator.

FIG. 3 shows a constant voltage circuit which has been conventionally used.

FIG. 4 is a diagram showing a circuit of a speedometer using a constant voltage circuit.

FIG. 5 is a diagram showing a power supply waveform and a sensor output waveform when chattering occurs in a switch after power is turned on.

[Explanation of symbols]

1 Control circuit 2 Comparator V _B Main power supply (battery voltage) V _CC Constant voltage

Claims (1)

[Scope of utility model registration request] 1. A constant voltage circuit for supplying a voltage supplied from a main power source to a load as a constant voltage, wherein the output voltage of the circuit can be operated for a predetermined time after the main power source is turned on. A constant voltage circuit characterized by comprising a control circuit for holding the voltage below a minimum voltage value.