JPH0668523B2 - Inverter power failure detection circuit - Google Patents

Description

Description: TECHNICAL FIELD [0001] The present invention detects a decrease in a power supply voltage of an inverter device, that is, a power failure, by detecting a voltage of a DC intermediate circuit of an inverter device by a zener voltage of a zener diode. The present invention relates to a power failure detection circuit for an inverter device.

[Prior art and its problems]

Generally, as a low voltage detecting circuit of this type, for example, the voltage of the DC intermediate portion of the inverter device is monitored, and the power source voltage of the input part of the inverter device is lost as in the case of a power failure or power interruption. There is known a low voltage detection circuit which is designed to stop the inverter device before the control system of the inverter device loses its function when the voltage of the DC intermediate portion is lowered to protect it from an accident. In this type of low voltage detection circuit, the voltage applied to the low voltage detection circuit when the input power source of the inverter device is sound and the voltage of the DC intermediate portion is normal, and the low voltage detection circuit is responsible for the operation. Since the voltage difference between the DC intermediate portion and the predetermined low voltage is generally large,
When the inverter device is operating normally, it is necessary to protect the low voltage detection circuit from overvoltage by some means. However, in the conventional low voltage detection circuit, the circuit configuration for providing the overvoltage protection means has a plurality of separations, which results in a heavy cost burden.

[Object of the Invention]

In view of the above-mentioned drawbacks associated with the conventional low voltage detection circuit having the protection means against the overvoltage required when the power source on the side where the low voltage is detected is normal, the present invention provides a simple means for detecting the voltage. An object of the present invention is to provide a power failure detection circuit for an inverter device, which is simple and economical in structure so that stable protection can be performed even for a voltage considerably higher than a predetermined low voltage for which an obligation is imposed.

[Main points of the invention]

In order to achieve such an object, the present invention has a zener diode, an appropriate constant current circuit, and a photocoupler connected in series, and connects both ends of a low voltage detection circuit to the positive electrode side of a DC intermediate circuit of an inverter device. And a negative side, a delay circuit is connected to the output side of the photocoupler, a flip-flop is connected to the output side of the delay circuit, and the photocoupler is turned on / off based on the voltage of the DC intermediate circuit of the inverter device. Thus, the power failure of the inverter device is detected through the delay circuit and the flip-flop.

That is, in the present invention, the photocoupler is turned on when the power supply voltage of the inverter device is normal, and is turned off when the power supply voltage drops to a predetermined low voltage. The on / off signal of the photocoupler is transmitted to the flip-flop via the delay circuit, and the flip-flop outputs a power failure detection signal of the inverter device and an inverter device stop signal for stopping the inverter device.

The delay circuit erroneously recognizes an instantaneous voltage drop in the power supply voltage of the inverter device as a power failure and prevents the flip-flop from issuing an inverter device stop signal.

Example of Invention

Next, the details of the present invention will be described based on the embodiments shown in the drawings.

FIG. 1 illustrates a low voltage detection circuit 1 in a power failure detection circuit of an inverter device according to the present invention, in which a zener diode 2, a well-known Emitta-follower type constant current circuit 3 and a photocoupler 4 are connected in series. The terminal A on the side of the Zener diode 2 of the detection circuit 1 is connected to the positive side of the DC power source 5 such as a DC intermediate section in the inverter device, and the terminal D of the side of the photocoupler 4 is connected to the negative side of the DC power source 5. Has been done.

On the other hand, when the voltage of the DC power supply 5 drops, in this case, when the voltage of the DC intermediate section 5 drops as a result of power failure or interruption of the input side power supply of the inverter device, the low voltage detection circuit 1 is interlocked with As a signal output means for stopping the inverter device, an RS flip-flop 9 is provided which is operated from a power source 6 via a series resistor 7, a delay circuit 8 including a capacitor, a resistor and a diode and an inverter 10. At the same time, 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.
A bypass circuit for the inverter device stop signal output circuit including the delay circuit 8 and the RS flip-flop 9 is formed via the phototransistor 4b.

In that case, in the low voltage detection circuit 1, the DC power supply 5, in this case the voltage of the DC intermediate portion of the inverter device exceeds the Zener voltage of the Zener diode 2, and the voltage between both terminals B and C of the constant current circuit 3, When the voltage between both terminals C and D of the photocoupler 4 reaches values at which the constant current circuit 3 and the photocoupler can operate, respectively, the low voltage detection circuit 1 is supplied to the low voltage detection circuit 1 via the constant current circuit 3 and the photodiode 4a of the photocoupler 4. An electric current flows. After that, even if the voltage of the DC intermediate part 5 of the inverter device becomes higher than the zener voltage of the zener diode 2, the collector-emitter voltage of the transistor 3a of the emitter-follower constant current circuit 3 rises accordingly, and the photocoupler 4 However, since a constant current always flows, the photocoupler 4 can always maintain a stable operation regardless of the voltage of the DC power supply 5.

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

However, when the voltage of the DC intermediate portion 5 decreases due to a power failure or interruption of the input power source of the inverter device, and the zener voltage of the zener diode 2, that is, a predetermined low voltage in this case, is reached, the RS constant current circuit 3, and thus again. Since the power supply to the photocoupler 4 is cut off, the photodiode 4
The phototransistor 4b which has been turned on by the energization of a is turned off, the inverter device stop signal circuit including the delay circuit 8 and the RS flip-flop 9 bypassed by the phototransistor 4b becomes conductive, and the flip-flop 9 outputs a signal. Then, the inverter device is stopped. In this case, the delay circuit 8 provided in series on the input side of the RS flip-flop prevents the RS flip-flop 9 from outputting a signal by erroneously recognizing an instantaneous voltage drop in the input power source of the inverter device as a power failure.

〔The invention's effect〕

As described above, the power failure detection circuit of the inverter device according to the present invention is configured such that a zener diode, an appropriate constant current circuit, and a photocoupler are connected in series, and both ends of the low voltage detection circuit are connected to the DC intermediate of the inverter device. The photocoupler is connected to the positive side and the negative side of the circuit, the delay circuit is connected to the output side of the photocoupler, the flip-flop is connected to the output side of the delay circuit, and the photocoupler based on the voltage of the DC intermediate circuit of the inverter device is connected. The power failure of the inverter device is detected through the delay circuit and the flip-flop by turning on / off the.

As a result, according to the present invention, it is possible to provide an economical power failure detection circuit for an inverter device that can reliably protect the inverter device from a power failure and can perform stable operation and protection of the photocoupler.

Further, according to the present invention, by connecting a delay circuit to the output side of the photocoupler, the delay circuit mistakenly recognizes an instantaneous voltage drop in the power supply voltage of the inverter device as a power failure, and the flip-flop causes the inverter device stop signal. Can be prevented from sending.

[Brief description 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 of an electric device. 1 ... Low voltage detection circuit, 2 ... Zener diode, 3
...... Constant current circuit, 4 ...... Photo coupler, 5 ...... Inverter device DC intermediate section voltage.

Claims (1)

[Claims] 1. A low voltage detection circuit configured by connecting a Zener diode, an appropriate constant current circuit, and a photocoupler in series is connected to the positive electrode side and the negative electrode side of a DC intermediate circuit of an inverter device, A delay circuit is connected to the output side of the photocoupler, a flip-flop is connected to the output side of the delay circuit, and the delay circuit and the flip-flop are connected by turning on / off the photocoupler based on the voltage of the DC intermediate circuit of the inverter device. A power failure detection circuit for the inverter device, characterized by detecting a power failure of the inverter device via the inverter.