JPH02214420A - Power supply circuit - Google Patents

Abstract

PURPOSE:To prevent erroneous operation of a drive circuit by providing a voltage monitoring circuit for monitoring supply voltage of a source circuit and turning a switching means OFF, when the supply voltage is lower than a predetermined level, to disable voltage supply to the drive circuit. CONSTITUTION:A switching means, i.e., a transistor 41, is arranged between a drive circuit 11 and a power source circuit 31, and a voltage monitoring means 51 for monitoring supply voltage of the power source circuit 31 and turning the transistor 41 OFF, when the supply voltage is lower than a predetermined level, to disable voltage supply to the drive circuit 11 is provided. The transistor 41 has emitter connected with the power source circuit 31 and collector connected with the buzzer 12 in the drive circuit 11. By such arrangement, drive voltage is not fed to the drive circuit 11 if the supply voltage from the power source circuit 31 is lower than a predetermined level when the power source is turned ON, for example.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a power supply circuit. In particular, when the supply voltage from the power supply circuit that supplies the drive voltage to the drive circuit is below a certain level, such as when the power is turned on, the drive circuit is prevented from malfunctioning. A power supply circuit having a power supply circuit that supplies a driving voltage to a drive voltage is known.

For example, as shown in FIG. 3, +
A power supply circuit is known that has a power supply circuit 31 that supplies a drive voltage of 15 cm and a control voltage of +5 cm, respectively.

Here, the drive circuit 11 includes a buzzer 12 and a transistor 13 inserted in series with the buzzer 12. Further, the control circuit 21 is constituted by a logic circuit, and its output signal is given to the base of the transistor 13. Note that 32 is a power switch, and 33 is a power plug.

Therefore, when the power switch 32 is turned on, the power supply circuit 31
A drive voltage of +15V is supplied to the drive circuit 11 and a control voltage of +5V is supplied to the control circuit #121, respectively, so if the transistor 13 is turned on by the output signal from the control circuit 21, the buzzer 12 is activated, that is, it sounds. be able to. Further, by turning off the transistor 13 using an output signal from the control circuit 21, the buzzer 12 can be stopped.

[Problem to be solved by the invention] In the circuit shown in FIG. 3, the gI control circuit 21 does not operate for a while after the power is turned on, that is, until the supply voltage from the power supply circuit 31 reaches a certain level. Since the output signal is unstable, there is a problem in that the drive circuit 11 malfunctions.

That is, as shown in FIG. 4, when the power is turned on, the control voltage supplied to the control circuit 21 and the drive voltage supplied to the drive circuit 11 gradually increase, but the control voltage
Since the output signal from the control circuit 21 is unstable until reaching 5■ and for a while after reaching +5■,
There was a problem in that the drive circuit 11 malfunctioned.

SUMMARY OF THE INVENTION An object of the present invention is to provide a power supply circuit that solves the conventional problems and prevents malfunction of the drive circuit.

[Means for Solving the Problems] Therefore, in the present invention, in a power supply circuit having a power supply circuit that supplies a drive voltage to a drive circuit, a switching means is provided between the drive circuit and the power supply circuit, and The present invention is characterized in that a voltage monitoring circuit is provided that monitors the voltage supplied from the power supply circuit and turns off the switching means to prohibit voltage supply to the drive circuit when the supply voltage is below a certain level.

[Operation] When the voltage supplied from the power supply circuit is below a certain level, the switching means is turned off and voltage supply to the drive circuit is prohibited. Therefore, when the supply voltage from the power supply circuit is below a certain level, for example, when the power is turned on, the drive circuit is not supplied with the drive voltage, so that malfunction of the drive circuit can be prevented.

[Example] Hereinafter, an example of the present invention will be described based on FIGS. 1 and 2. In the description of these figures, the same components as those in FIG. 3 are given the same reference numerals, and the description thereof will be omitted.

In this embodiment, as shown in FIG. 1, a transistor 41 as a switching means is provided between the drive circuit 11 and the power supply circuit 31, and
1 and turns off the transistor 41 when the supply voltage is below a certain level.
A voltage monitoring circuit 51 is provided that prohibits voltage supply to.

The transistor 41 has an emitter connected to the power supply circuit 31 and a collector connected to the buzzer 12 of the drive circuit 11.

The voltage monitoring circuit 51 includes a Zener diode 53 connected to the base of the transistor 41 via a resistor 52, and a ## between the base and emitter of the transistor 41.
, and a connected resistor 54. Here, the Zener diode 53 used has an IOV whose breakdown voltage is higher than the control voltage of 15V and lower than the drive voltage of +15V.

In such a configuration, as shown in FIG. 2, when the power is turned on, the control voltage and the supply voltage gradually rise.At this time, until the supply voltage reaches +10V, the Zener diode 53 is turned on. Therefore, the base current of transistor 41 does not flow, and therefore transistor 41 remains off. In this state, the buzzer 12
Since the drive voltage remains at OV during this period, even if the output signal from the control circuit 21 is unstable, the buzzer 12 will not sound, which means that malfunction of the drive circuit 11 can be prevented.

Eventually, when the supply voltage reaches +10V, the Zener diode 53 turns on. Then, since the transistor 41 is also turned on, the voltage from the power supply circuit 31 is supplied to the drive circuit 11 through the transistor 41, and the drive voltage of the drive circuit 11 rises to approximately +15. In this state, since the output signal of the control circuit 21 is also stable, the drive circuit 11 can be operated normally by the output signal from the control circuit 21.

Therefore, according to this embodiment, the drive circuit 11 and the power supply circuit 3
1, a voltage monitor that monitors the voltage supplied from the power supply circuit 31 and turns off the transistor 41 when the supply voltage is below a certain level to prohibit voltage supply to the drive circuit 11. Since the circuit 51 is provided, the drive circuit 11 does not operate in an unstable state where the voltage supplied from the power supply circuit 31 is below a certain level, such as when the power is turned on, so malfunction of the drive circuit 11 in this state can be prevented. Can be done.

In the above embodiment, the voltage monitoring circuit 51 is composed of the Zener diode 53 and the resistors 52 and 54, but it may be composed of a comparator.

In this case, the supply voltage from the power supply circuit 31 may be compared with a reference voltage, and when the supply voltage is at a level lower than the reference voltage, the transistor 41 constituting the switching means may be turned off.

In addition, in the above embodiment, a buzzer is used as an example of the drive circuit, but the drive circuit is not limited to this. For example, in an electronic cash register, a printer head drive circuit, a paper feed motor drive circuit, etc. It can also be applied to a drive circuit for a magnet that locks a drawer.

[Effects of the Invention] As described above, according to the present invention, a switching means is provided between a drive circuit and a power supply circuit, and the supply voltage from the power supply circuit is monitored, and when the supply voltage is below a certain level, the switching means Since a voltage monitoring circuit is provided to turn off the power supply circuit and prohibit voltage supply to the drive circuit, when the voltage supplied from the power supply circuit is below a certain level, the switching means is turned off and voltage supply to the drive circuit is prohibited. Therefore, when the voltage supplied from the power supply circuit is below a certain level, such as when the power is turned on, no drive voltage is supplied to the drive circuit, so that malfunction of the drive circuit can be prevented.

Figure 1

[Brief explanation of the drawing]

1 and 2 show an embodiment of the present invention,
FIG. 1 is a circuit diagram, and FIG. 2 is a timing chart. 3 and 4 show conventional power supply circuits, with FIG. 3 being a circuit diagram and FIG. 4 being a timing chart. DESCRIPTION OF SYMBOLS 11... Drive circuit, 31... Power supply circuit, 41... Transistor (switching means), 51...
...Voltage monitoring circuit. Figure 2 5■

Claims (1)

[Claims] (1) In a power supply circuit having a power supply circuit that supplies a drive voltage to a drive circuit, a switching means is provided between the drive circuit and the power supply circuit, and a switching means is provided between the drive circuit and the power supply circuit, and the voltage supplied from the power supply circuit is monitored. A power supply circuit comprising: a voltage monitoring circuit that turns off the switching means and prohibits voltage supply to the drive circuit when the voltage is below a certain level.