JPS5840838B2 - induction heating cooker - Google Patents

Description

Detailed Description of the Invention In an induction heating cooker that uses a frequency converter, the load current and frequency vary depending on the type and size of the pot serving as the load, due to variations in inductance forming a resonant circuit and increases in input voltage. However, the input current also fluctuates.

However, when using a switching semiconductor, there is a limit to the current flowing through the switching semiconductor, and various problems arise such as turn-off failure due to an increase in temperature of the switching semiconductor case.

Therefore, the present invention detects the input current and input voltage, and when the input current and input voltage become larger than the initial set level, increases the non-conduction time of the switching semiconductor so that the current flowing through the switching semiconductor increases. By suppressing the value, stable operation is guaranteed.

Hereinafter, a specific example will be described based on the drawings.

FIG. 1 shows a wiring diagram of an induction cooking device comprising a frequency conversion circuit 10 and its control circuit 19. As shown in FIG.

The frequency conversion circuit 10 converts the commercial power supply 1 into a full-wave rectification circuit 2.
The high-frequency current bypass capacitor 3 is connected between the output terminals of the rectifier.

A choke coil 4 is connected to the positive output terminal of the full-wave rectifier circuit 2.
One end of the series circuit of the resonant capacitor 6 and the resonant inductor 7 is connected, and the other end is connected to the negative terminal of the full-wave rectifier circuit 2.

Then, the switching semiconductor block 5 is connected in parallel with the series circuit of the resonant capacitor 6 and the resonant inductor 7.

The switching semiconductor block 5 includes a thyristor 51 in the forward direction and a diode 52 in antiparallel.

When the frequency conversion circuit 10 is used as an induction heating cooker, the resonant inductor 7 is used as a heating coil to heat the pot 8.

The current transformer 9 is installed on the input side of the full-wave rectifier circuit 2.

FIG. 2 shows a block diagram of the control circuit 19.

The gate timing circuit 18 detects the voltage between the terminals of the switching semiconductor block 5 from the terminals B-D, and when it reaches a certain predetermined level, the vF detection circuit 11 outputs an output signal, and the vF detection circuit 11 outputs the output signal. A delay circuit 1 that outputs a signal after a certain delay time after outputting the signal.
2. triggered by the output signal of the delay circuit 12;
It consists of a mono-stable circuit 13 that forms constant pulses.

Further, 14 is a gate drive circuit driven by the pulse signal of the mono-stable circuit 13, 15 is an Iin detection circuit that outputs a DC voltage in one-to-one correspondence with the input current by the current transformer 9, and 16 17 is a comparison circuit, and 17 is a Vin detection circuit that outputs a DC voltage corresponding to the voltage of the commercial power supply 1 on a one-to-one basis. The higher level is compared with a preset level, and if a signal higher than the preset level is input, the delay time of the delay circuit 12 is extended (this increases the gate signal period). The control circuit 19 is configured to output operation signals such as the above.

FIG. 3 is a detailed diagram of the control circuit.

The voltage between the terminals of the switching semiconductor block 5 is divided by the resistors 110 and 111 using the terminals B-D, and when the voltage exceeds the Zener voltage of the Zener diode 112, the transistor 114 is turned on, the transistor 120 is turned off, and the capacitor 125 is connected to the resistor 124. charged through.

Then, the voltage across the terminals of the capacitor 125 is
, 127, the output of the comparator 129 becomes rHJ and triggers the mono-stable circuit 13.

The output of the mono-stable circuit 13 operates the gate drive circuit 14, causing a gate current to flow in the direction from the terminal G to the terminal.

The gate drive circuit 14 connects a series circuit of a resistor 141 and a pulse transformer 143 to the collector of a transistor 144 from a DC power source VOO, and connects the pulse transformer 14 to the collector of a transistor 144.
A diode 142 is connected between the terminals of the pulse transformer 3 to absorb the rebound voltage of the pulse transformer.

A resistor 1 is connected to the secondary terminal of the ballast transformer 143.
A 45°146 series circuit is connected, and the terminal G1 terminal K is connected from both ends of the resistor 146.

When the gate current from the gate drive circuit 14 turns on the thyristor 51, the voltage becomes the voltage between terminals B and D, turning off the transistor 114 and turning on the transistor 120.
turns on.

The capacitor 125 is then discharged through the resistor 121.

The above operating state is shown in FIG.

In FIG. 4, a is a high frequency resonant current waveform, b is a voltage waveform between terminals B and D, is a voltage waveform between the terminals of the capacitor 125, d is an output waveform of the comparator 129,
e indicates the output waveform of the mono-stable circuit 13.

On the other hand, the terminals cl and C2 are connected to the current transformer 9, and the voltage between the terminals of the resistor 150 is connected to the diodes 151 to 154.
It passes through a full-wave rectifier circuit and is rectified to a DC voltage level by a capacitor 155.

Note that the resistor 156 is for discharging the capacitor 155, and is of high resistance.

In addition, the terminal A is connected to the high frequency current bypass capacitor 3.
It is connected to the positive terminal of the commercial power supply 1, divided by resistors 170 and 171, and rectified by a capacitor 113 to obtain a DC voltage corresponding to the voltage of the commercial power supply 1 on a one-to-one basis.

Note that the resistor 172 is for discharging the capacitor 173, and is of high resistance.

The Iin detection circuit 17°Vin obtained as described above
The higher of the output DC voltages of the detection circuit 15 is input to the comparison circuit 16.

If the input voltage is lower than the initially set level, resistor 164
．． The voltage is divided by a resistor 165 and connected to the base of the transistor 163 so that the anode voltage of the diode 166 is lower than the cathode voltage during normal operation.

When an input voltage is input to the base of the transistor 160 and becomes higher than the base voltage of the transistor 163, the diode 166 becomes conductive, pushing up the negative input terminal voltage of the comparator 129 in the delay circuit 12,
It works to increase the delay time.

As described above, according to the present invention, when at least one of the input current and the power supply voltage reaches a predetermined level or higher, the period of the gate signal that makes the switching semiconductor conductive becomes longer, so that the high-frequency current value automatically decreases, and the high-frequency current value of the switching semiconductor is automatically reduced. The stable switching operation is guaranteed, and
Even if the power supply voltage increases, the input power can be kept almost constant, and even if the inductance component of the resonant circuit changes depending on the type or size of the pot, the input current value can be automatically controlled to be below a predetermined level.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a frequency conversion circuit and its control circuit for an induction heating cooker according to an embodiment of the present invention, FIG. 2 is a block diagram of the control circuit, and FIG. 3 is a detailed diagram of the control circuit. FIG. 4 is a diagram showing waveforms of various parts of the control circuit. 5...Semiconductor block, 6...Resonance capacitor, 7...Resonance inductor, 10.
...Frequency conversion circuit, 14...Gate
Drive circuit, 15...Iin detection circuit, 16
... Comparison circuit, 17 ... Vin detection circuit, 18 ... Gate timing circuit, 19 ...
...control circuit.

Claims (1)

[Claims] 1. A full-wave rectifier connected to an AC power supply, a series circuit consisting of a heating coil and a resonant capacitor connected to the output terminal of this full-wave rectifier, a switching semiconductor connected in parallel to this series circuit, and this switching semiconductor. The control circuit detects the voltage between the terminals of the switching semiconductor, and outputs a signal to turn on the switching semiconductor after a certain period of time after the voltage between the terminals reaches a predetermined level. An induction heating cooker comprising: a gate timing circuit; and means for lengthening the predetermined time when at least one of the input current of the AC power supply and the voltage of the AC power supply is higher than a predetermined level.