JPS6033595Y2 - induction heating cooker - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to an induction heating cooker.

Conventionally, in induction heating cookers, the input waveform of the commercial AC power supply is irregular and one cycle is missing, or the power supply is cut off momentarily due to chattering that occurs when the power switch is turned on. If this occurs, the circuit that controls the inverter will not operate properly due to a drop in the drive power supply voltage, and for example, the on/off time of the switching elements that make up the inverter will be delayed, causing a large current to flow through this and causing damage. It was occurring.

The present invention has been developed in view of these circumstances, and one embodiment will be described below based on the drawings.

In Figure 1, 1 is an AC power supply, 2 is a power switch, and 3
The rectifier circuit 4, which is made up of bridge-connected diodes, is a filter circuit and consists of a chock coil 5 and a smoothing capacitor 6. The capacitance of this capacitor 6 is set small, and the voltage obtained from this is a pulsating voltage that is hardly smoothed. It becomes.

Reference numeral 7 is an induction coil to which direct current power is supplied through the filter circuit 4, and is wound into a flat plate shape and placed close to the back surface of the top plate 8 made of a ceramic plate or the like.

9 is a cooking pot made of iron, stainless steel, etc. placed on the top plate 8; 10 is a switching element connected in series with the induction coil 7; in this embodiment, GC3 (gate controlled switch) (product name); I am using it.

Reference numeral 11 indicates a flywheel diode connected in antiparallel between the anode and cathode of ccs 1 g, and reference numeral 12 indicates a resonant capacitor. Ru.

This inverter 13 is of an operation type called a self-limiting inverter, and starts oscillating in response to a starting signal provided by a starting signal generating circuit 14, and thereafter continues oscillating in response to a gate signal issued from a gate signal generating circuit 15.

16 gives a positive or negative signal to the gate of GC8IQ,
An inverter drive circuit 17 that turns on and off the inverter drive circuit 17 is a flip-flop that controls the inverter drive circuit 16 and is operated by a start signal and a gate signal.

19 is a first rectifying and smoothing circuit to which the AC power supply voltage is applied via the step-down transformer 18, and its output voltage is 10 Vcc.
(approximately 8 V) is supplied to the activation signal generation circuit 14, gate signal generation circuit 15, inverter drive circuit 16, etc. as a drive power source.

Here, the starting signal generating circuit 14 provides the first starting signal for the inverter 13, and oscillates at a predetermined period, for example, a 0.4 second period, and once the oscillation starts, its operation is prohibited until the oscillation is stopped.

Furthermore, the gate signal generation circuit 15 generates a trigger pulse for self-controlled oscillation and gives an on/off signal to the gate of CCS1G. The flip-flop 17 is set by the side induction coil voltage Vc, and a signal is applied to the gate of ccs 1 g to make it conductive.

After that, due to conduction of ccs1g, the output voltage of the current transformer 20 wound on the cathode side of the induction coil 7
When it becomes larger than the input side type IEVA, the flip-flop 17 is reset and GCSlo is cut off.

As a result, the energy stored in the induction coil 7 is charged into the resonant capacitor 12, and subsequently, the capacitor 12 starts discharging.

When this discharge ends, the energy accumulated in the induction coil 7 during this period flows through the diode 11, and when this discharge ends and the voltage between the anode and cathode of ccs 1 g changes from negative to positive, GC3I Q becomes conductive again. death,
The next oscillation cycle begins.

Note that during the conduction period of the diode 11, the voltage Ve becomes negative, and this negative signal applies an on signal to the gate of α310, and the moment the anode-cathode voltage changes to positive, it becomes conductive.

In this way, self-controlled oscillation continues, and its oscillation frequency is approximately 2
The frequency is 0 to 40KHz.

Reference numeral 21 denotes a power supply voltage detection circuit to which AC power is applied via the transformer 18, and is connected to the input side of the flip-flop 17 to control it.

A specific example of this power supply voltage detection circuit 21 is shown in FIG.

In the figure, 22 is a comparator, and the reference potential V- obtained by dividing the power supply voltage ■CC by a resistor 23.24 is applied to the input terminal.
On the other hand, at the input terminal, an AC signal obtained from a transformer 18 (Fig. 1) is rectified by diodes 25 and 26, further smoothed through a resistor 27 and a capacitor 28, and then passed through a resistor 29.
．． It is divided into 30 parts and inputted.

That is, the diode 25.degree. 26, the resistor 27, and the capacitor 28 constitute a second rectifying and smoothing circuit.

Further, here, the time constant determined by the resistor 27 and the capacitor 28 is made shorter than the falling time constant of the control power supply voltage Vcc supplied to the start signal generation circuit 14, gate signal generation circuit 15, and inverter drive circuit 16 described above. There is a need.

This is because the control power supply voltage Vcc decreases with the time constant of each control section described above due to a momentary power interruption, and the voltage detection circuit 21 must be activated to stop the oscillation of the inverter 13 before reaching the inoperable potential. This is because it must be done.

Next, the operation of the above configuration will be explained using FIG. 3.

Currently, commercial AC power supplies are used for short periods of up to several 100m5ec (
(represented by T in the figure), control power supply voltage Vc
As shown by waveform A, c gradually decreases from a normal value of 8V to about 7V.

If this voltage drops to about 7V, the inverter drive circuit 16 in particular will not operate properly, delaying the on-time of the GC3IQ, causing a large current to flow through the CCS 10, which may destroy it.

Therefore, the oscillation of the inverter 13 must be stopped before the voltage reaches about 7V.

That is, when such a situation occurs, as shown in waveform B, the output of the time constant circuit consisting of the resistor 27 and capacitor 28 becomes less than the reference voltage V- before the control voltage reaches the inoperable value (represented by time t), and the comparison is made. The output of the device 22 is changed to the L level as shown by waveform C.

This L level signal fixes the flip-flop 17 in the oscillation stopped state.

Note that the part indicated by the broken line in the waveform B in FIG. 3 shows the waveform when the AC power obtained through the transformer 18 is rectified by the diodes 25 and 26, and shows the state in which l waveforms are missing in the period T. .

As described above, the induction heating cooker of the present invention includes a control circuit system that controls the oscillation of the inverter, a first rectifying and smoothing circuit that rectifies and smoothes the AC power supply and supplies it to the control circuit system, and a momentary interruption of the AC power supply. a power supply voltage detection circuit that detects and provides a stop signal to the control circuit system to instruct the control circuit to stop oscillation;
This power supply voltage detection circuit rectifies and smoothes the AC power supply, and compares and detects a decrease in the output of this second rectifier and smoothing circuit with a second rectifier and smoothing circuit having a shorter time constant than the first rectifier and smoothing circuit. , and comparison means for giving a stop signal to the control circuit system, so that only instantaneous interruptions in the AC power supply can be quickly detected without stopping or restarting oscillation in synchronization with the troughs of the full-wave rectified voltage. This is detected and the inverter oscillation is stopped before the voltage to the control circuit system drops, thereby preventing incomplete operation of the control circuit system.

Therefore, it is possible to prevent the switching element from being destroyed due to incomplete operation of the control circuit system, without causing discomfort to the user due to the activation platform.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram of the main parts on the same side, and FIG. 3 is a waveform diagram for explaining the operation on the same side. 14... Start signal generation circuit, 15...
Gate signal generation circuit, 16... Inverter drive circuit, 17... Flip-flop, 21. Song.
Power supply voltage detection circuit.

Claims (1)

[Scope of utility model registration request] An AC power source, a full-wave rectifier circuit that performs full-wave rectification of this AC power source, a smoothing capacitor that smoothes the output of this full-wave rectifier circuit, an inverter circuit that receives the voltage smoothed by this smoothing capacitor, and an inverter circuit that receives the voltage smoothed by this smoothing capacitor. A control circuit system that controls the oscillation of this inverter circuit while detecting oscillation operation, a first rectifying and smoothing circuit that rectifies and smoothes the AC power source and supplies it to the control circuit system, and detects momentary interruption of the AC power source. and a power supply voltage detection circuit that provides a stop signal to the control circuit system to instruct the control circuit to stop oscillation. an induction heating cooker comprising: a second rectifying and smoothing circuit having a second rectifying and smoothing circuit; and comparison means for comparatively detecting a decrease in the output of the second rectifying and smoothing circuit and providing a stop signal to the control circuit system.