JPS62265576A - Low voltage detecting circuit - Google Patents

Abstract

PURPOSE:To attain stable protection even against a voltage which is much higher than a specific low voltage by a simple means by connecting a Zener diode, a constant current circuit, and a photocoupler to the positive and negative terminals of a power source to be detected. CONSTITUTION:When the voltage at the DC intermediate part of an inverter device exceeds the Zener voltage of the Zener diode 2, a current is conducted to a low voltage detecting circuit 1 through the constant current circuit 3, photocoupler 4, and photodiode 4a and the photocoupler 4 is put in invariably stable operation regardless of the voltage of a DC power source 5. When the voltage at the DC intermediate part 5 drops owing to the power failure or disconnection of the input power source of the inverter device, electric feeding through the constant current circuit 3 and photocoupler 4 is cut off, so a phototransistor 4b turns off and the inverter device stop signal circuit consisting of a delay circuit 8 and an RS flip-flop 9 conducts and a flip-flop outputs a signal, thereby stopping the inverter device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a low voltage detection circuit that detects a drop in power supply voltage using the Zener voltage of a Zener diode and protects electrical equipment.

[Prior art and its problems]

In general, this type of low voltage detection circuit monitors the voltage at the DC intermediate part of an inverter, for example, and detects when the power supply voltage at the input part of the inverter is lost, such as in the case of a power outage or disconnection of the power supply. A low voltage detection circuit is known that protects the inverter from an unexpected accident by stopping the inverter before the control system of the inverter loses its function when the DC intermediate voltage drops. In this type of low voltage detection circuit, when the input power source of the inverter device is healthy and the voltage of the DC intermediate section is normal, the voltage applied to the low voltage detection circuit and the low voltage detection circuit are responsible for operation. Generally, the voltage difference between the DC intermediate section and the predetermined low voltage is large.
When the inverter device is operating normally, it is necessary to protect the low voltage detection circuit from overvoltage by some means. However, the conventional low voltage detection circuit has the drawback that the circuit configuration for providing the overvoltage protection means is separate, which increases the cost burden.

[Purpose of the invention]

In view of the above-mentioned drawbacks associated with conventional low voltage detection circuits that are provided with protection against overvoltage that is necessary when the power supply on which low voltage is detected is normal, the present invention provides a simple means for detecting low voltage. It is an object of the present invention to provide a simple and economical low voltage detection circuit that provides stable protection even against voltages considerably higher than a predetermined low voltage to which it is responsible.

[Key points of the invention]

In order to achieve the above object, in the present invention, in a low voltage detection circuit, a circuit formed by connecting the Zener diode and a photocoupler with an appropriate constant current circuit in series is connected between the positive and negative terminals of the power source to be detected. When the voltage of the power supply is normal, the photocoupler is turned on, and when the voltage of the power supply drops to a predetermined low voltage, the photocoupler is turned off and the electricity is turned off. By making the low voltage protection means of the device work, when the voltage of the power supply is normal, the low voltage detection circuit of the electrical device is bypassed and the protection function does not function, and the voltage of the power supply is normal. The photocoupler turns off when the voltage drops to a predetermined low voltage, thereby enabling a signal circuit for operating the low voltage protection means of the electrical device to operate.

[Embodiments of the invention]

Next, the present invention will be explained in detail based on embodiments shown in the drawings.

In the low voltage detection circuit 1 of the present invention illustrated in FIG. 1, a Zener diode 2 and a well-known emitter follower type
! The L flow path 3 and the photocoupler 4 are connected in series, and the terminal A on the side of the Zener diode 2 of the low voltage detection circuit 1 is connected, for example, to a DC intermediate part in an impark device.
The current is connected to the positive side of the source 5, and its terminal on the photocoupler 4 side is connected to the negative side of the DC power source 5.

On the other hand, when the voltage of the DC buffer source 5 decreases, in this case, the voltage of the DC intermediate section 5 decreases as a result of a power outage or cutoff of the input power supply of the inverter device, the low voltage detection circuit 1 is activated. As a signal output means for stopping the inverter device, an RS flip 70 tube 9 is operated from t@6 via a series resistor 7, a delay circuit 8 consisting of a capacitor, a resistor, and a diode, and an inverter 10. is provided, and the collector terminal of the phototransistor 4b of the photocoupler 4 of the low voltage detection circuit 1 is connected to the low voltage side terminal G of the series resistor 7,
Through the phototransistor 4b7i, a bypass circuit is formed for the inverter production stop signal output circuit consisting of the delay circuit B and the AS flip 70 tube 9.

In that case, in the low voltage detection circuit 1, the DC current fA5,
In this case, the voltage at the DC intermediate portion of the inverter device exceeds the Zener voltage of the Zener diode 2, and the constant current circuit 3
The open voltage between both terminals B and C of the photocoupler 4 and the voltage between both terminals C and D of the photocoupler 4 are constant current amounts VI! r3
When the current reaches the low voltage detection circuit 1 via the constant current circuit 3 and the photodiode 4a of the photocoupler 4, the voltage at the DC intermediate section 5 of the inverter device reaches the Zener diode 2. Even if the Zener voltage becomes higher than the Zener voltage of Regardless of the voltage or power, the photocoupler 4 can always maintain stable operation.

As described above, as a result of energizing the photodiode 4a of the photocoupler 4, the phototransistor 4b becomes conductive, establishing a bypass circuit that passes the reference potential 10 from the power supply 6 through the resistor 7 and the phototransistor 4b, and the delay circuit 8 and the RS flip-flop 9. Since the inverter stop signal circuit consisting of is bypassed, no signal is output from flip-flop 9.

However, due to a power outage or cutoff of the input power source of the inverter device, the voltage of the DC intermediate section 5 decreases and reaches the Zener voltage of the Zener diode 2, that is, a predetermined low voltage in this case, R8 constant 71! , the wave circuit 3, and therefore also the force that cuts off the current flow in the photocoupler 4), the phototransistor 4b, which had been turned on due to the energization of the photodiode 4a, is turned off, and the delay circuit 8, which had been bypassed by the phototransistor 4b, is turned off. R,S flip-flop 9
The inverter stop signal circuit made up of the following becomes conductive, and the flip-flop 9 outputs a signal to stop the inverter. In this case, the delay circuit 8 provided in series on the input side of the RS flip-flop mistakes the instantaneous voltage drop in the input power supply of the inverter device as a power outage, and
This prevents the flip-flop 9 from outputting a signal.

〔Effect of the invention〕

As explained above, the present invention provides a low voltage detection circuit that detects a drop in power supply voltage using the Zener voltage of a Zener diode and protects electrical equipment, which combines the Zener diode, an appropriate constant current circuit, and a photocoupler. A circuit connected in series is connected between the positive and negative terminals of the power source to be detected, and when the voltage of the power source to be detected is normal, the photocoupler is turned on and the voltage of the power source to be detected is reduced. The photocoupler is turned off when the voltage reaches a predetermined low voltage, thereby activating an appropriate low voltage protection means for the electrical device, thereby ensuring low voltage protection of the electrical device. This is an economical low voltage detection circuit that can stably operate and protect the photocoupler by connecting the low voltage detection circuit to the photocoupler which is supplied with power through a Zener diode and a constant current circuit. It has the effect of realizing

[Brief explanation of drawings]

FIG. 1 shows a schematic connection diagram of a low voltage detection circuit according to the present invention and a low voltage protection signal circuit for an electrical device. 1...Low voltage detection circuit, 2...Zener diode,
3... Constant current circuit, 4... Photocoupler, 5... Inverter device DC intermediate voltage.

Claims (1)

[Claims] 1) In a low voltage detection circuit designed to protect electrical equipment by detecting a drop in power supply voltage using the Zener voltage of a Zener diode, the Zener diode, an appropriate constant current circuit, and a photocoupler are connected in series. A circuit is connected between the positive and negative terminals of the power source to be detected, and when the voltage of the power source to be detected is normal, the photocoupler is turned on, and the voltage of the power source to be detected decreases to a predetermined level. 1. A low voltage detection circuit, characterized in that the photocoupler is turned off when a voltage is reached, thereby activating appropriate low voltage protection means of the electrical device.