JPS6334234Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention relates to an electromagnetic cooker that induction heats cooking pots, etc., and particularly relates to a protection device for an electromagnetic cooker.

(b) Conventional technology As disclosed in Japanese Patent Application Laid-Open No. 53-30049, in conventional electromagnetic cookers, after turning on the power switch,
In a no-load state where the appropriate load such as a cooking pot is not placed on the load mounting table, the system detects this and issues a warning sound or lights up an indicator such as a lamp to warn you. Ta.

(c) Problems to be solved by the invention In the conventional structure described above, when it is detected that the load placed on the load mounting table is unloaded (including the load of small objects), the display element blinks. Let me,
Although an attempt was made to notify that there was no load, the heating coil was still energized from the power supply. That is, the power supply to the inverter circuit that generates high-frequency alternating current is stopped, and the high-frequency current to the heating coil is cut off, but the power supply from the low-frequency alternating current (commercial alternating current) power source is not stopped. For this reason, in the case of a small load, heating is not performed properly as during normal operation, but heating is performed at a minimal output, resulting in wasted power consumption. Also,
After the power switch is turned on, heating preparations are always made, and heating is started when the load is detected.

For this reason, the present invention automatically stops power supply after a certain period of time when no load is detected when no load is placed on the load mounting table, thereby reducing unnecessary power consumption and increasing safety. The purpose is to improve sexual performance.

(d) Means for solving the problems The present invention solves the above problems, and includes:
The following will be explained based on examples.

An inverter circuit that is inserted into a power line and includes a power supply circuit 1 that includes a power switch 2 and a power transformer 3, and a heating coil that is supplied with power by this power supply circuit 1 and that inductively heats a load by continuing its self-excited oscillation. 5, a load detection circuit 7 that detects the presence or absence of a load placed on a load mounting table located above the heating coil and sends a signal based on the detection, and a control circuit that sends a start signal to the inverter circuit 5. 6
and. It is connected to the load detection circuit 7 and starts timekeeping operation upon receiving the no-load detection signal.
A timer circuit 8 for sending out a time-up signal after a certain period of time, and a relay circuit 9 including an excitation coil L connected to the timer circuit 8 and a stabilized power supply circuit 4 and energized until the time-up signal is input are provided. When the time-up signal is input, the relay circuit 9 opens the relay contact 9a to cut off the power supply.

(e) Effect When the no-load detection signal is sent from the load detection circuit 7, charging of the capacitor _C1 in the timer circuit 8 is started. When the charging voltage of capacitor C ₁ exceeds the breakover voltage, PUT ₁ becomes conductive and PUT ₂ becomes conductive, and a time-up signal (base current to transistor Q ₁ ) of timer circuit 8 is output. When this time-up signal is input, the energization to the excitation coil L is stopped, and the relay contact 9a, which had been closed until then, is opened.

(f) Example An example of the present invention will be described below based on the drawings. FIG. 1 is a block diagram of the circuit according to the present invention, in which 1 is a power switch 2 inserted into the power line.
and a relay contact 9 connected in parallel to this switch 2
a. A power supply circuit consisting of power transformers 3 connected in series, and the power supply circuit 1 includes a load mounting table (not shown).
An induction heating coil (not shown) installed at the bottom of the
An inverter circuit 5 including the following is connected. The inverter circuit 5 oscillates in response to the activation signal from the control circuit 6, and inductively heats the load placed on the load mounting table.

A stabilized power supply circuit 4 is provided on the secondary side of the power transformer 3, and the power supply voltage V _DD is supplied to the load detection circuit 7 and the timer circuit 8 via the stabilized power supply circuit 4.
and is supplied to the relay circuit 9 and the like.

The load detection circuit 7 includes a diode _D1 and
It has a NOT circuit (INV) on its output end side and detects the presence or absence of a load placed on the load mounting table.When a load presence state, that is, a normal load state is detected, the NOT circuit (INV) Sends a lower level signal and connects a NOT circuit (INV) when detecting a no-load condition
Sends out a higher level signal. Timer circuit 8
By sending out a no-load detection signal, that is, a high-level signal, from the load detection circuit 7, time is measured for a certain period of time, for example, about 3 minutes. During timekeeping, an on signal is sent to a relay circuit 9 as a cut-off means to be described later, and an off signal (time-up signal) is sent out after timekeeping. That is, at the output end of the stabilized power supply circuit 4, a series circuit of resistor R ₁ and capacitor C ₁ , a series circuit of resistors R ₃ and R ₄ , and anode-cathode connection of the second programmable UJT (PUT ₂ ) are connected. and a series circuit with a resistor R ₆ are connected in parallel. and the connection point A between resistor R ₁ and capacitor C ₁
The first programmable UJT via resistor R ₂
Connect the anode of (PUT ₁ ) and ground the cathode. Furthermore, the gate of (PUT ₁ ) is connected to the connection point B between resistors R ₃ and R ₄ . Furthermore, resist the gate of PUT ₂
Connect to V _DD through R ₅ and capacitor C ₂
Connect to point B via. Let C be the connection point between this resistor _R5 and the capacitor _C2 .

The relay circuit 9 receives the output of the timer circuit 8 and
V _DD controls the opening and closing of the relay contact 9a. That is, connect the base of the first transistor Q ₁ to the cathode of PUT ₂ via the resistor R ₇ ,
Its emitter is grounded, and its collector is connected to V _DD via a resistor R ₈ and to the base of the second transistor Q ₂ via a resistor R ₉ . The emitter of the second transistor _Q2 is grounded, and the collector is connected to _VDD via the excitation coil L. The excitation coil L closes the relay contact 9a in its energized state, and opens the relay contact 9a in its de-energized state.

Further, in this embodiment, the case where two programmable UJTs are used in the timer circuit 8 is shown, but the resistors R ₅ and R ₆ and the capacitor C ₂ and PUT ₂ in FIG. 2 are omitted. A resistor may be connected to the cathode of PUT ₁ , and the cathode may be connected to resistor _R7 .

The configuration of the present invention is as described above, and its operation will be explained below.

By turning on the power switch 2, _VDD is sent to the output terminal of the stabilized power supply circuit 4, and power is supplied to the inverter circuit 5.
Then, when a start signal is sent from the control circuit 6,
Inverter circuit 5 is activated. At this time, when the load detection circuit 7 detects the presence of a load on the load mounting table, a low level signal is sent from the NOT circuit (INV) in the load detection circuit 7, and the diode _D1 becomes forward biased. , conducts and pulls the potential at point A to a low level. Then, since the potential at point A in the timer circuit 8 does not exceed the breakover voltage of PUT ₁ determined by the potential at point B, PUT ₁ is in an off state. Therefore, the breakover voltage of PUT ₂ determined by the potential at point C, which is higher than the potential at point B, is higher than the anode-cathode voltage, and PUT ₂ is also in an off state. In this state, the first transistor Q ₁ of the relay circuit 9
Since no base current flows through the transistor Q2, it is turned off, and the second transistor _Q2 becomes conductive to excite the excitation coil L. Therefore, the relay contact 9a is closed, and normal operation, that is, induction heating of the load due to self-oscillation of the inverter circuit 5 is performed. In addition, the power switch 2 is
It is assumed that the switch remains ON only for the time it is pressed.

On the other hand, when the load detection circuit 7 detects no load on the load mounting table (including the load of small objects), NOT
A high level signal is sent out from the circuit (INV), and diode _D1 becomes reverse biased and becomes non-conductive. Therefore, capacitor _C1 is charged, and when this charging voltage exceeds a breakover voltage determined by the potential at point B, _PUT1 becomes conductive.
Then, draw the potential at point B to approximately earth level,
The potential at point C is lowered than the potential at point C under normal operation. This also reduces the breakover voltage and makes PUT ₂ conductive. and,
A base current flows through the first transistor _Q1 , turning it on, and the second transistor Q1 is turned on.
Turn Q ₂ off. By turning off the second transistor _Q2 , the excitation coil L is de-energized and the relay contact 9a is opened.
The power supply to the inverter circuit 5 is cut off. Therefore, no load is detected by the load detection circuit 7, charging by the capacitor _C1 is started, and after a certain period of time until the charging voltage exceeds the breakover voltage of PUT ₁ , the power supply to the inverter circuit 5 is cut off. do.

Here, since the power supply to the inverter circuit 5 is cut off after a certain period of time has passed after the detection of no load, it is possible to remove the load from the mounting table after cooking and forget to turn off the power at this time. Even if the inverter circuit 5
The power is cut off to improve safety. Furthermore, even if a load is placed again, power will not be supplied unless the power switch 2 is turned on, so safety is improved in this respect as well.

Furthermore, since the power supply from the power supply circuit 1 to the inverter circuit 5 is cut off after a certain period of time when no load is detected, there will be no unnecessary power consumption in the inverter circuit 5 thereafter.

By the way, ensuring a certain period of time after detecting no load before cutting off the power supply to the inverter circuit 5 has the following advantages. In other words, if the load is temporarily removed from the mounting table as needed to create a no-load state, if the configuration is such that the power supply is cut off immediately after no-load is detected, the load will continue to function normally even if the load is re-mounted. cannot be heated by induction. However, in this embodiment, when the load is temporarily removed within a certain period of time, the power supply is not cut off in any way, so that normal induction heating will continue when the load is placed again. It is possible.

(g) Effects of the invention According to the invention, when no load is detected, the power supply to the inverter circuit is cut off after a certain period of time, so there is no chance of forgetting to turn off the power when the load is removed after cooking or during cooking. Even if something happens, the power will automatically shut off after a certain period of time, making it extremely safe. Furthermore, once the power supply to the inverter circuit is cut off, there is no unnecessary power consumption in the inverter circuit, which is economical. Furthermore, even if the load becomes unloaded by temporarily removing the load for the specified period of time, the power supply will not be cut off undesirably, and therefore, if the load is then placed again, the load will not be interrupted. Normal induction heating continues and is practical.

[Brief explanation of the drawing]

Each figure shows one embodiment of the present invention; FIG. 1 is a schematic block circuit diagram of the cooking device, and FIG. 2 is a main part electrical circuit diagram. 5...Inverter circuit, 7...Load detection circuit,
8...Timer circuit, 9...Relay circuit, 9a...
...Relay contact.

Claims (1)

[Scope of utility model registration request] An inverter circuit that inductively heats a load, a power supply circuit that supplies power to the inverter circuit, a control circuit that drives the inverter circuit supplied with power by the power supply circuit to oscillate, and a control circuit that detects the presence or absence of a load. A load detection circuit that sends out a signal, a timer circuit that starts time measurement based on the no-load detection signal from the load detection circuit and outputs a time-up signal after a certain period of time, and a time-up signal from the timer circuit that causes the power supply circuit to connect to the inverter circuit. A protection device for an electromagnetic cooker, comprising: a cutoff means for cutting off power supply to the electromagnetic cooker.