JPH10208858A - Induction heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the generation of overheat and failures due to the deterioration of driving characteristic to be generated by the lowering of driving voltage by separately stopping drive of a drive circuit from operation of a control unit so as to stop the operation of a switching element in the case where low voltage of a switching element driving power source is detected by a voltage detecting circuit. SOLUTION: A voltage detecting circuit 11 is formed by connecting an intermediate point of a series circuit of a Zener diode 110, which is connected to a switching element driving power source, and a resistor 111 to a base of a transistor 113 through a resistor 112, and connecting a collector of the transistor 113 to a pull-up resistor 114 and a base of a transistor 115. With this structure, in the case where the switching element driving power source is lower than the Zener voltage, the transistor 113 is turned off, and the transistor 115 is turned on. As a result, since input of a drive circuit 12 is stopped independently of the pulse output condition of a control circuit 9, IGBT is not driven.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for an induction heating device.

[0002]

2. Description of the Related Art Induction heating systems are widely used as heat sources for tabletop cookers, rice cookers and the like. These devices use a microcomputer for the control part, and provide key input, display,
Used for heating control. The switching element for the heating inverter is IGBT (Insulated Gate Bipoler Tra)
nsister) is mainly used. The power supply voltage of the control microcomputer is 5V, while the IGBT is usually 15V.
Since a driving voltage of about V is required, there are two power supply circuits.

[0003]

As described above, two power supplies are usually required, and when the drive voltage of the IGBT is reduced due to a drop in the voltage of the AC power supply or a failure in the power supply circuit, the switching characteristics of the elements deteriorate. Causes overheating and damage.

[0004] Even when a control microcomputer has a program for detecting a drop in AC power supply voltage, it takes several tens of milliseconds or more to detect an instantaneous low voltage and stop heating. If the IGBT drive voltage decreases during that time, the above-described situation occurs.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and includes a rectifier circuit for converting an AC power supply to a DC power supply, a smoothing circuit for smoothing the DC power supply, and a smoothing circuit. An inverter for converting the output of the inverter into a high-frequency current by a switching element, supplying the high-frequency current to a resonance circuit including a heating coil, a capacitor, and a load to heat the load;
In an induction heating apparatus including a control unit that controls the inverter unit, a power supply circuit that supplies power to a drive circuit for driving the control unit and the switching element, and a voltage detection circuit that detects a power supply voltage supplied to the drive circuit. ,
When the voltage detection circuit detects a low voltage, the drive of the drive circuit is stopped separately from the operation of the control unit, and the operation of the switching element is prohibited.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention detects a decrease in the output of a power supply circuit for driving a switching element separately from the operation of a control unit, and automatically stops the driving of the switching element. An induction heating device can be provided.

[0007]

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

FIG. 1 is a block diagram of a main part of an induction heating apparatus showing one embodiment of the present invention.

A commercial power supply 1 is converted to a DC power supply by a rectifier 2 and smoothed by a smoothing circuit composed of a choke coil 3 and a capacitor 4. A switching circuit composed of a switching element 7 and a diode 8 connected in anti-parallel are connected to a resonance circuit composed of the heating coil 5 and the capacitor 6, a high-frequency current flows through the resonance circuit, and a load disposed near the heating coil 5. Heat.

A control circuit 9 constituting a control section generates pulses for driving the switching element 7 from various inputs. The pulse is transmitted to the drive circuit 12 via the voltage detection circuit 11. The drive circuit 12 amplifies the pulse to drive power sufficient to drive the switching element 7.

The power supply circuit 10 supplies a power supply V1 for driving the switching element and a power supply V2 for the control circuit. V1 is connected to the voltage detection circuit 11 and the drive circuit 12.

FIG. 2 shows a configuration example of the control circuit 9, the voltage detection circuit 11, and the drive circuit 12.

The output pulse form of the control circuit 9 will be described as an open collector output in which a pull-up resistor is connected to V2. The output is connected to an input terminal of the drive circuit 12.

The voltage detecting circuit 11 is connected to a series circuit of a Zener diode 110 and a resistor 111 connected to V1, and connected from the middle point to the base of a transistor 113 via a resistor 112, and has a collector connected to a pull-up resistor 114 and a transistor 115 Connect the base. With such a configuration, when V1 is higher than the Zener voltage, the transistor 113 is turned on, and the transistor 115 is turned on.
Is turned off. When V1 becomes lower than the Zener voltage, the state of each transistor is inverted.

Therefore, when V1 decreases and the transistor 115 is turned on, the input of the drive circuit 12 is stopped regardless of the state of the pulse output of the control circuit 9, and the IGBT is not driven.

FIG. 3 shows an example of operation waveforms when the voltage drops. Waveform A is the voltage of the power supply V1, waveform B is the ON / OFF state of the transistor 115, and waveform C is the input waveform of the drive circuit 12. Until time T1, V1 is higher than the Zener voltage, so that the transistor 115 is turned off, and the input waveform of the drive circuit 12 remains the output waveform of the control circuit 9.

From time T1 to T2, V1 is lower than the Zener voltage, so that the transistor 115 is turned on and the output of the control circuit 9 is not transmitted, so that the input waveform of the drive circuit 12 becomes low level and the IGBT is not driven.

Further, as shown in FIG.
The same effect can be obtained even when the configuration position of the drive circuit 12 and the drive circuit 12 are exchanged.

[0019]

A rectifier circuit for converting an AC power supply to a DC power supply, a smoothing circuit for smoothing the DC power supply, and a switching element for converting the output of the smoothing circuit into a high-frequency current, the resonance comprising a heating coil, a capacitor and a load An inverter unit for supplying heat to the circuit and heating the load; a control unit for controlling the inverter unit; a power supply circuit for supplying power to a drive circuit for driving the control unit and the switching element; and a power supply for supplying power to the drive circuit In the induction heating device including a voltage detection circuit that detects a voltage, when the voltage detection circuit detects a low voltage, the driving of the drive circuit is stopped separately from the operation of the control unit, and the operation of the switching element is prohibited. Therefore, when the drive voltage of the switching element is lowered due to a drop in AC power supply voltage or a failure in the power supply circuit, the drive characteristics may deteriorate. It is possible to reduce the occurrence of overheating and component failure.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of an induction heating apparatus according to an embodiment of the present invention.

FIG. 2 is a detailed circuit diagram of a main part in the same manner.

FIG. 3 is an operation waveform diagram.

FIG. 4 is a block circuit diagram of an induction heating apparatus showing another embodiment of the present invention.

[Explanation of symbols]

9: control circuit, 10: power supply circuit, 11: voltage detection circuit,
12 ... Drive circuit.

Claims (1)

[Claims] 1. A rectifier circuit for converting an AC power supply to a DC power supply, a smoothing circuit for smoothing the DC power supply, and a switching element for converting an output of the smoothing circuit into a high-frequency current, and comprising a heating coil, a capacitor and a load. An inverter unit for supplying heat to the circuit and heating the load; a control unit for controlling the inverter unit; a power supply circuit for supplying power to a drive circuit for driving the control unit and the switching element; and a power supply for supplying power to the drive circuit In the induction heating device including a voltage detection circuit that detects a voltage, when the voltage detection circuit detects a low voltage of a switching element driving power supply, the driving of the drive circuit is stopped separately from the operation of the control unit, and the switching is performed. An induction heating device characterized in that the operation of the element is prohibited.