JPH0648634B2 - Induction heating cooker - Google Patents

Description

TECHNICAL FIELD The present invention relates to an induction heating cooker used in a general household.

2. Description of the Related Art Conventionally, an induction heating cooker of this type has an inverter including a switching element, a drive circuit having at least one transistor, and a control circuit connected to the drive circuit to control conduction and non-conduction of the switching element. The control circuit outputs a signal that causes the switching element to be non-conductive when the power supply voltage of the control circuit is equal to or lower than a predetermined threshold value, and provides a delay when the power supply voltage is equal to or higher than the threshold value. To activate the switching element.

Problems to be Solved by the Invention In such a conventional configuration, when the power supply voltage of the control circuit is very low, the operation of the control circuit becomes incomplete,
As a result, there is a problem in that the switching element may be erroneously turned on, and the switching element is easily destroyed.

In view of the above problems, the present invention surely makes the switching element non-conductive by making the transistor non-conductive even when the power supply voltage of the control circuit is very low, prevents destruction of the switching element, and is reliable. It is intended to provide an induction heating cooker having high properties.

Means for Solving the Problems In order to achieve this object, the induction heating cooker of the present invention comprises:
An inverter including a switching element, a drive circuit connected to the switching element having at least one transistor, a control circuit connected to the drive circuit for controlling conduction / non-conduction of the switching element, and a base current of the transistor A constant voltage element inserted in the supply portion, the drive circuit makes the switching element non-conductive regardless of the power supply voltage of the control circuit when the transistor is non-conductive, and the power supply voltage is the first voltage. Below the threshold, the transistor becomes non-conductive, and the control circuit determines that the power supply voltage is at least the first level.
A signal for non-conducting the switching element from a threshold value of 2 to a second threshold value higher than the threshold value, and providing a delay when the power supply voltage exceeds the second threshold value. The switching element is started, and the power supply voltage is the first
Below the threshold value, the switching element is configured to be non-conductive regardless of the type of signal of the control circuit.

By this configuration, by making the transistor non-conductive even when the power supply voltage of the control circuit is very low,
It is possible to surely make the switching element non-conductive, prevent the switching element from being erroneously made conductive, and prevent the switching element from being broken.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of an induction heating cooker according to an embodiment of the present invention. In the figure, 1 is a switching element 2
An inverter 3 including a transistor 3 is a transistor 4 and a resistor 6,
7 is a drive circuit configured by 7. 8 is a drive circuit 3
Is a control circuit connected to the power supply voltage detection circuit 9 and the activation delay circuit 1 for controlling conduction and non-conduction of the switching element 2.
0 and the oscillation circuit 11. The power supply voltage detection circuit 9 is composed of a constant voltage element 12, resistors 13, 14 and 15, and a comparator 16. The output of the comparator 16 is the power supply voltage V of the control circuit 8, the first threshold value V ₁ , and the second threshold value V ₁ . Due to the relationship of the threshold value V ₂ of the above, when V ≧ V ₁ , it is opened, and when V ≦ V ₂ , it is pulled to GND. The start-up delay circuit 10 includes a capacitor 17 and resistors 18, 19 and 2
0 and the comparator 21, the output of the comparator 21 is pulled to GND when the output of the comparator 16 is pulled to GND, and when the output of the comparator 16 is opened from GND, a fixed time elapses. Then, when the voltage of the capacitor 17 exceeds the voltage at the midpoint between the resistors 19 and 20, the capacitor 17 becomes open. Oscillator circuit 11
Has a transistor 22, and the transistor 22 repeats conduction and non-conduction at high frequency. A constant voltage element 23 is connected in series with the resistor 24 and supplies a base current from the power supply terminal of the control circuit 8 to the transistor 4 when the power supply voltage V is higher than the first threshold value V ₁ . A power supply circuit 25 supplies a power supply voltage V to the control circuit 8.

In the above configuration, the drive circuit 3 includes the transistor 4
Is non-conducting, the switching element 2 is non-conducting regardless of the magnitude of the power supply voltage V, the transistor 4 is non-conducting when V ≦ V ₁ , and the control circuit 8 controls the power supply voltage detecting circuit 9 and the startup delay circuit 10. Due to the action, at least V ₁ <V
At <V ₂ , the base of the transistor 4 is pulled to GND to make the switching element 2 non-conductive, and when V ≧ V ₂ , a delay is provided and the switching element 2 is activated. That is, in the circuit of the present embodiment, when V ≦ V ₁ , the transistor 4 becomes non-conductive and the switching element 2 becomes non-conductive regardless of whether the output of the control circuit 8 is open or is pulled to GND. Become. Therefore, even if the control circuit 8 becomes unstable when the power supply voltage V is a constant voltage V ₃ or less, V
By the _1> V _3, to ensure non-conductive switching element 2 in the range of 0 <V <V _2, if it becomes V ≧ V ₂ can be activated by a delay.

In the present embodiment, when the power supply voltage detection circuit 9 and the startup delay circuit 10 are omitted and only the circuit including the high voltage element 23 and the resistor 24 is used, the switching element 2 is prevented from conducting when V <V _3. However, when V is in the vicinity of V ₁ , the operation of the transistor 4 and the switching element 2 becomes unstable, and since there is no startup delay, the switching element may be destroyed.

EFFECTS OF THE INVENTION As is clear from the above embodiments, the induction heating cooker according to the present invention has an inverter including a switching element, a drive circuit having at least one transistor, and a drive circuit connected to the switching element, and the drive circuit. Connected to the control circuit for controlling conduction / non-conduction of the switching element, and a constant voltage element inserted in a base current supply portion of the transistor, and the drive circuit includes a control circuit of the control circuit when the transistor is non-conduction. Regardless of the power supply voltage, the switching element is made non-conductive, and when the power supply voltage is equal to or lower than the first threshold value, the transistor becomes non-conductive, and the control circuit sets the power supply voltage at least from the first threshold value to Outputting a signal that renders the switching element non-conductive until a high second threshold value,
When the power supply voltage is equal to or higher than the second threshold value, a delay is provided to activate the switching element, and when the power supply voltage is equal to or lower than the first threshold value, the switching element is irrespective of the type of signal of the control circuit. By making the switching element non-conductive by making the transistor non-conductive even when the power supply voltage of the control circuit is very low by making it non-conductive, and by preventing the switching element from conducting accidentally. It is possible to provide a highly reliable induction heating cooker that prevents the switching element from being destroyed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an induction heating cooker according to an embodiment of the present invention. 1 ... Inverter, 2 ... Switching element, 3 ... Drive circuit, 4 ... Transistor, 8 ... Control circuit, 2
3 ... Constant voltage element.

Claims (1)

[Claims] 1. An inverter including a switching element, a drive circuit having at least one transistor connected to the switching element, and a control circuit connected to the drive circuit for controlling conduction / non-conduction of the switching element. A constant voltage element inserted in the base current supply portion of the transistor, the drive circuit renders the switching element nonconductive regardless of the power supply voltage of the control circuit when the transistor is nonconductive. When the voltage is equal to or lower than the first threshold, the transistor becomes non-conductive, and the control circuit keeps the switching element off while the power supply voltage is at least from the first threshold to a second threshold higher than the first threshold. A signal for continuity is output, and a delay is provided when the power supply voltage exceeds the second threshold value. Start switching element, induction heating cooker wherein the power supply voltage is below said first threshold switching element non-conductive regardless of the type of signal of the control circuit.