JPH0640509B2 - Heater - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heater such as an electromagnetic cooker for heating an object to be heated by induction heating, and particularly, a power supply circuit is constituted by a DC-DC converter and a secondary coil. The present invention relates to prevention of destruction of an existing DC-DC converter.

<Prior Art> FIG. 5 is a circuit diagram of a conventional electromagnetic cooker. This circuit performs full-wave rectification on a commercial low-frequency AC power source 1 by a rectifier circuit 2 (rectifier stack), and one of the rectified outputs is a smoothing capacitor 3, a resonance capacitor 4, a heating coil 5, and a switching. Element 6 and diper diode 7
To the inverter circuit 8 and the other is smoothed by the capacitor 10 via the diode 9 and the DC-DC
It is flowing to the converter 11.

Reference numeral 12 denotes a power supply circuit, which is an output of the DC-DC converter 11 and a secondary coil 13, which is inductively coupled to the heating coil 5,
Each of the 14 outputs is input. The output of the power supply circuit 12 forms a power supply for driving the switching element 6 and a power supply for operating the timing circuit 15, the triangular wave generation circuit 16, the drive pulse generation circuit 17, the output control circuit 18, and the drive circuit 19. In the figure, 20 is a secondary coil,
21 is a current lance and 22 is a DC-DC converter 1
1 transistor.

FIG. 3 shows the voltage waveform across the smoothing capacitor 3, but before the inverter circuit 8 operates, it is almost 141V.
Is. However, the low frequency AC power supply 1 is 100V.

Next, when the inverter circuit 8 operates, the smoothing capacitor 3
By adjusting the capacity of, the full-wave rectified waveform remains.

Generally, an electromagnetic cooker has a smoothing capacitor 3 with a capacity of several M
Since it is selected from F to 10 MF, the voltage drops to the vicinity of zero as shown in FIG.

Since the DC-DC converter 11 uses the voltage of the smoothing capacitor 3 as an input source, it operates stably before the inverter circuit 8 operates. However, if the inverter circuit 8 operates, both ends of the smoothing capacitor 3 will operate. When the voltage becomes close to zero, the DC-DC converter 11 causes oscillation failure, and when the transistor 22 is turned on while the converter transistor 22 is overvoltage exceeding its rated voltage, the collector-emitter voltage is increased. Exceeds the maximum collector voltage and destroys the transistor 22.

The conventional one uses a smoothing capacitor 3 to compensate for this drawback.
The voltage obtained by smoothing the voltage of 1 through the diode 9 with the capacitor 10 was used as the input source of the DC-DC converter 11. However, the capacitor 10 requires a large voltage and a large capacity, resulting in a cost increase and a large size, which is contrary to the miniaturization of the set of the electromagnetic cooker itself.

<Objective> In view of the above, the present invention has an object to provide a heater that can be reduced in cost and downsized.

<Embodiment> An embodiment of the present invention will be described below mainly with reference to FIGS. 1 and 2. A heater as an electromagnetic cooker according to the present invention is connected to a low-frequency AC power source 1, a rectifier circuit 2, An inverter circuit 8 having a heating coil 5, a switching element 6 and the like, a control device S for driving and controlling the switching device 6, and a power supply circuit 12 for supplying electric power to the control device S are provided. An output of a DC-DC converter 11 having an output DC voltage of the rectifier circuit 2 as an input source, and a secondary coil 13 inductively coupled to the heating coil 5,
14 is provided, and a converter stop circuit 23 for stopping the oscillation of the DC-DC converter 11 is provided substantially in synchronization with the driving of the switching element 6.

The controller S includes a drive circuit 19 that drives the switching element 6, a drive pulse generation circuit 17 that outputs a pulse signal to the drive circuit 19, and a triangular wave generation circuit 16 that outputs a triangular wave signal to the drive pulse generation circuit 17. An output control circuit 1 for outputting a control signal to the drive pulse generation circuit 17
8 and a timing circuit 15 for outputting a timing signal to the triangular wave generation circuit 16 are provided.

In the inverter circuit 8, the heating coil 5 is connected to the DC side output terminal of the rectifier circuit 2 via the smoothing capacitor 3, and the switching element 6 and the damper diode 7 are connected in parallel to the heating coil 5 and the resonance capacitor 4. Connected in parallel. The switching element 6 is a transistor, the base side of which is connected to the drive circuit 19.

Secondary coils 20 for outputting signals to the secondary coils 13 and 14 for the power supply circuit 12 and the timing circuit 15 are arranged on the secondary side of the heating coil 5.

In the DC-DC converter 11, a converter transistor 22 is connected to the DC side output terminal (plus side) of the rectifier circuit 2 via a primary coil of a converter transformer 24, and the emitter side of the converter transistor 22 is rectified. It is connected to the DC side output terminal (negative side) of the circuit 2. The converter stop circuit 23 is connected to the base side of the converter transistor 22.

The converter stop circuit 23 is, for example, as shown in FIG.
It comprises a converter stopping transistor 25, the collector A side of which is connected to the base side 22a of the converter transistor 22, and the emitter B side of the stopping transistor 25 is connected to the emitter 22b side of the converter transistor 22. It The base side of the stopping transistor 25 is connected to the input terminal of the output control circuit 18.

The other structure is the same as the conventional structure shown in FIG.

In the above configuration, when the inverter circuit 8 operates and the transistor as the switching element 6 is driven, the High signal is input from the output control circuit 18 to the converter stop circuit 23.

The DC-DC converter 11 performs self-excited oscillation with the converter transistor 22 and the converter transformer 24. However, if the self-excited oscillation is stopped, the DC-DC converter 11 stops, and the DC-DC converter 11
The transistor 22 will not be destroyed by any value of the input voltage.

There are various methods of stopping the self-excited oscillation, but the simplest method is to short the base of the converter transistor 22 and the emitter.

In this example, the converter stop circuit 23 has a transistor 25.
The collector of the stopping transistor 25 is
Between the emitters, the base 22a of the converter transistor 22 and the emitter 22b are shorted. When a High signal is input to the base of the stop transistor 25 from the output control circuit 18, the stop transistor 25 is turned on.
However, the converter transistor 22 is shut down due to a short between the base and the emitter.

If the inverter circuit 8 operates, the secondary coil 13,
Due to the voltage induced by 14, the power supply circuit 12 obtains a voltage substantially equal to that before the operation of the inverter circuit 8, and thus the power supply circuit 12 operates without any problem.

With the above-described configuration, the abnormal operation of the DC-DC converter 11 can be prevented with a simple method and with small-sized components, and the operation time of the converter transformer 24 can be shortened. The rated value of 24 can be set low, the size of the converter transformer 24 can be small, and the size of the set can be further reduced.

The present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention. For example, in the inverter circuit 8 in the above embodiment, it goes without saying that the primary side of the high voltage transformer may be connected instead of the heating coil 5. The emitter side B of the stop transistor 25 may be connected to a voltage level lower than the emitter level of the converter transistor 22.

<Effect> As is apparent from the above description, according to the present invention, the DC-DC converter serving as the input source of the power supply circuit for supplying the electric power to the control device that drives and controls the switching element is for performing self-excited oscillation. An output control circuit of the control device is provided which has a converter transistor and a converter transformer, and which stops the self-excited oscillation of the DC-DC converter during operation of the inverter circuit to protect the transistor. Is turned off by the stop signal output from the output control circuit in synchronization with the control signal output from the switch to the switching element, and the DC-
The oscillation of the DC converter can be stopped.

Therefore, when the voltage of the DC power supply for driving the heating coil falls below a certain value, it is possible to prevent the transistor from being destroyed due to the oscillation failure of the DC-DC converter, and also to shorten the operating time of this transistor and reduce the rating. If it can be done with the transistor, it will have an excellent effect.

Moreover, since the converter stop circuit can be composed of, for example, one transistor, the abnormal operation of the DC-DC converter 11 can be prevented by a simple method and with a small-sized component.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an electromagnetic cooker showing an embodiment of the present invention,
2 is a circuit diagram of the same part, FIG. 3 is a diagram showing a voltage across the smoothing capacitor before the operation of the inverter circuit, FIG. 4 is a diagram showing a voltage across the smoothing capacitor during operation of the inverter circuit,
FIG. 5 is a circuit diagram of a conventional electromagnetic cooker. 1: Low-frequency AC power supply, 2: Rectifier circuit, 3: Smoothing capacitor, 4: Resonance capacitor, 5: Heating coil, 6: Switching element, 7: Damper diode, 8: Inverter circuit, 11: DC-DC converter, 12 : Power circuit,
13, 14: Secondary coil, 15: Timing circuit, 1
6: triangular wave generation circuit, 17: drive pulse generation circuit, 1
8: output control circuit, 19: drive circuit, 22: converter transistor, 23: converter stop circuit, 24: converter transformer, 25: converter stop transistor, S: control device.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Hiromi Togawa 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture Sharp Corporation (56) References 58-60893 (JP, U)

Claims (1)

[Claims] 1. An inverter circuit which is connected to a low frequency AC power supply and has a rectifier circuit, a primary coil, a switching element, etc., and an input current to the inverter circuit is detected to output a control signal to the switching element to output the switching element. And a power supply circuit for supplying electric power to the control device, wherein the power supply circuit uses a DC voltage output from the rectifier circuit as an input source.
The output of a DC converter and the output of a secondary coil that is inductively coupled to the primary coil. The DC-DC converter includes a converter transistor and a converter transformer for performing self-excited oscillation, and the inverter circuit. Is provided, a converter stop circuit for stopping the self-excited oscillation of the DC-DC converter to protect the transistor is provided, and the output control circuit sends the converter stop circuit to the converter stop circuit in synchronization with the control signal output to the switching element. A heater comprising means for turning off the transistor according to the output stop signal.