JPH0720376B2 - Inverter circuit - Google Patents

Description

The present invention relates to an inverter circuit equipped with a microcomputer for controlling the speed of an induction motor.

<Prior Art> In the conventional method, the _IF power supply circuit is controlled by an original circuit regardless of the reset signal, and the circuit includes a Zener diode or a diode at the output port of the microcomputer as shown in FIG. A method of connecting and controlling by the potential or a method of controlling by the input / output voltage difference of the stabilized power supply circuit as shown in FIG. 3 has been used.

The <INVENTION A problem to be solved> this conventional method, fast I _F power supply circuits operate than the reset signal instantaneous input power to the circuit configuration is complicated by the occurrence of instantaneous reduction to the pulse generating circuit In that case, the photocoupler in the pre-driver circuit is stopped at a certain moment and the power transistor group is activated at the operating frequency, and an excessive collector current flows and the overcurrent protection circuit operates. Also, when operating slowly I _F power supply circuits than the reset signal, it is necessary to care the minimum operating voltage of the microcomputer and the overcurrent protection circuit in the pulse generating circuit.

The present invention has been devised in view of the above point and has a simple configuration, and an object of the present invention is to reliably protect the power transistor group together with the overcurrent protection circuit against the occurrence of momentary interruption and momentary drop of the input power supply. Circuit.

<Means for Solving Problems> As means for solving the above problems, the present invention relates to a power transistor group (3) for converting a DC power supply into an AC power supply and switching the power transistor group (3). A pulse generation circuit (7) centering on a microcomputer for generating a signal to generate a pre-driver circuit (6) using a photo coupler corresponding to the interface between the power transistor group (3) and the pulse generation circuit (7); and I _F power supply circuit for supplying a photocoupler forward current of the pre-driver circuit (6) (9), when the pulse generation circuit power supply voltage supplied to detect a power supply voltage detection is lower than the reference voltage and outputs a reset signal, said with initializes the microcomputer of the pulse generating circuit I _F power supply circuit (9) the OFF-like And a power supply monitoring circuit (8) that controls the photocoupler of the predriver circuit (6) to prevent an abnormal current from flowing through the inverter circuit.

<Operation> The power supply monitoring circuit (8) detects a decrease in the control circuit power supply voltage, and resets to prevent unspecified operation during a power supply voltage lower than the operation guarantee voltage of the microcomputer. Keep giving a signal.

Furthermore, also continue to issue a certain time reset signal after the power supply voltage is restored to the steady state, controls the I _F power supply circuit and a microcomputer.

<Embodiment> FIG. 1 is a block diagram of an inverter circuit of the present invention. In FIG. 1, 1 is an input power source, 2 is a rectifier circuit for converting an AC power source into a DC power source, and 3 is a DC power source. A group of power transistors 4 for converting into an AC power source is an induction motor.

In the control circuit section, 5 is a control circuit power supply, 6 is a pre-driver circuit for operating the power transistor group 3 using a photocoupler, 7 is a pulse generation circuit centered on a microcomputer, and 8 is a reset signal (81). power supply monitoring circuit, 9 is I _F power supply circuit for supplying a forward current to the photocoupler of the pre-driver circuit 6 is controlled by a reset signal.

The power supply monitoring circuit 8 is a circuit for accurately detecting a decrease in the control circuit power supply voltage, and as shown in FIG. 4, unspecified operation during a power supply voltage lower than the operation guarantee voltage (Vs) of the microcomputer. It is a circuit that keeps outputting a reset signal in order to prevent the above-mentioned operation, and also has a function that keeps outputting a reset signal for a certain period of time after the power supply voltage returns to a steady state.

The I _F power supply circuit 9 and the microcomputer are controlled by the power supply monitoring circuit 8.

FIG. 5 shows an embodiment according to the present invention, in which a high-level active system reset input (RESET) device is used for the microcomputer in the pulse generation circuit 7, and the power supply monitoring circuit 8 also uses it. Use a voltage detection system reset IC that is compatible with (RESET). FIG. 4 shows an operation example of the power supply monitoring circuit 8.

The operation will be described below. First, the control circuit power supply 5
Voltage is applied from V to V ⁺ , and when the voltage value reaches the microcomputer operation guarantee voltage (Vs), the voltage detection system reset IC holds high level for a preset delay time (td), and eventually It goes low and the microcomputer program is started. At the same time, a base current flows through the PNP transistor 10 via the base current limiting resistor, and the transistor 10 is turned on.

Therefore, a voltage is applied to the anode of the light emitting diode in the photo coupler in the pre-driver circuit 6, each photo coupler forward current ( _IF ) flows according to the output pulse of the pulse generation circuit 7, and the switching of the power transistor group 3 is performed. It is started and its output drives the induction motor 4.

The output of the voltage detection system reset IC is an open collector and is pulled up by a resistor connected to the output terminal, and the capacitor absorbs external noise. Then, a resistor connected to the collector of the transistor 10 flows leakage current when the transistor 10 is OFF, I _F power supply voltage (1
01) is set to 0V. Next, when a power failure occurs in the input power source I and the voltage of the control circuit power source 5 drops to Vs, the voltage detection system reset IC outputs a high level to initialize (stop) the program of the microcomputer. At the same time, the transistor 10 is turned off.

Therefore, even if the level of the DC voltage of the rectifier circuit 2 is high, the _IF power supply voltage (101) is 0V, and even if the output logic of the pulse generation circuit 7 is unstable, the pre-driver circuit 6 does not operate, The switching of the power transistor group 3 is completely stopped. That is, even if a power failure occurs, the power transistor group 3 can be surely protected.

In addition, the voltage of the control circuit power supply 5 decreases due to the momentary power failure.
Even if Vs becomes Vs or less and Vs abnormally recovers immediately, the voltage detection system reset IC still has {time below Vs + delay time (t
It is a reset IC that can hold a high level during d)} and always initializes the microcomputer program to prevent runaway.

Although the voltage detection reset IC in which the number of components is reduced is used in the above embodiment, it is also possible to assemble it with discrete components such as a comparator. Also, an opto-IC having a photo-coupler function can be used as the pre-driver circuit 6.

In addition, although the use of the inverter for the induction motor as the electric motor 4 is illustrated, the present invention is also applicable to the inverter for the DC electric motor in which the magnet is attached to the rotor.

<Effects of the Invention> As described above, according to the present invention, it is possible to protect the power transistor group against the occurrence of instantaneous interruption and instantaneous decrease of the input power supply with an extremely simple circuit configuration.

[Brief description of drawings]

FIG. 1 is a block diagram of an inverter circuit of the present invention, FIG. 2 is a circuit diagram showing an embodiment of an _IF power supply circuit conventionally used, and FIG. 3 is another _IF power supply circuit conventionally used. FIG. 4 is an explanatory view of an operation example of the power supply monitoring circuit of the present invention, and FIG. 5 is a circuit diagram showing an embodiment of the _IF power supply circuit of the present invention. 1: Input power supply, 2: Rectifier circuit, 3: Power transistor part, 4:
Induction motor, 5: control circuit power supply, 6: pre-driver circuit,
7: pulse generation circuit, 8: power supply monitoring circuit, 9: _IF power supply circuit.

Claims (1)

[Claims] 1. A power transistor group (3) for converting a DC power source into an AC power source, a pulse generating circuit (7) mainly comprising a microcomputer for generating a signal for switching the power transistor group (3), Pre-driver circuit (6) using a photo coupler corresponding to the interface between the power transistor group (3) and the pulse generation circuit (7), and the pre-driver circuit (6)
I _F power supply circuit for supplying a photocoupler forward current (9)
When the together with the power supply voltage detected by the detecting power supply voltage supplied to the pulse generation circuit outputs a reset signal when lower than the reference voltage, to initialize the microcomputer of the pulse generating circuit I _F Power circuit (9)
An inverter circuit comprising a power supply monitoring circuit (8) for controlling an off state to prevent an abnormal current from flowing in the photocoupler of the pre-driver circuit (6).