JPS62198083A - Cooker - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention 1 (Field of Industrial Application) This invention relates to a cooking appliance in which power is supplied to a magnetron by an inverter circuit.

(Prior Art) Generally, in a cooking device such as a microwave oven, an inverter circuit is used which converts AC power supply voltage into DC and then converts it into AC voltage at a predetermined frequency (several tens of kHz) by switching and outputs the AC voltage. There is a device in which the output of this inverter circuit is boosted and rectified and applied to the magnetron. That is, by varying the output frequency of the inverter circuit, it is possible to continuously adjust the heating output steplessly.

(Problems to be Solved by the Invention) By the way, in such a microwave oven, if a short circuit occurs between the anode and cathode of the magnetron, or a short circuit occurs in the high voltage capacitor for rectification between the inverter circuit and the magnetron. There is a problem in that even the switching elements in the inverter circuit are damaged due to this influence.

This invention was developed in view of the above circumstances, and its purpose is to prevent damage to elements in an inverter circuit in the event of a short circuit between the anode and cathode of a magnetron or a short circuit of a high voltage diode. Our goal is to provide a highly reliable cooker that can.

[Structure of the Invention] (Means for Solving the Problems) An inverter circuit that once converts AC power supply voltage to DC and then converts it to AC voltage of a predetermined frequency and outputs it, and the output of this inverter circuit is boosted and rectified. The inverter circuit comprises a magnetron that applies a signal, a frequency detecting means for detecting the output frequency of the inverter circuit, and a means for stopping the operation of the inverter circuit when the detected frequency of the frequency detecting means exceeds a predetermined value.

(Function) If a short circuit occurs between the anode and cathode of the magnetron or a short circuit occurs in the high voltage diode, excessive current will flow through the elements of the inverter circuit, creating a dangerous situation. At this time, the output frequency of the inverter circuit increases above a predetermined value, so
This is detected and the operation of the inverter circuit is stopped.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

1 is a commercial AC power supply, and this power supply 1 is connected to a diode bridge 2. A rectifier circuit 5 consisting of a choke coil 3° for noise removal and a smoothing capacitor 4 is connected. A series resonant circuit consisting of the primary coil 6a of the high-voltage transformer 6 and the capacitor 1 is connected to the output end of the rectifier circuit 5, and the capacitor 7 is connected to the collector-emitter of a switching element such as an NPN transistor 8 and a regenerative diode. (damper diodes) 9 are connected in parallel.

On the other hand, the anode and cathode of the magnetron 12 are connected to the secondary coil 6b of the high voltage transformer 6 via a half-wave voltage doubler rectifier circuit consisting of a high voltage capacitor 10 and high voltage diodes 11a and 11b. And magnetron 1
The anode of No. 2 is grounded, and the heater (cathode) is connected to a heater N source (not shown) via a transformer 13.

That is, the rectifier circuit 5. A series resonant circuit consisting of the primary coil 6a of the transformer 6 and the capacitor 7, and a transistor 8 that excites this resonant circuit. The regenerative diode 9 constitutes an inverter circuit, and the inverter circuit supplies power to the magnetron 12.

Further, 20 is a tIlI control section consisting of a microcomputer and its peripheral circuits, and the base of the transistor 8, the operating section 21, etc. are connected to this section 111111.

The control unit 20 includes a microcomputer 30. - A voltage feedback circuit 31 that extracts the voltage across the primary coil 6a, an oscillation circuit 32 that emits a "sawtooth" signal according to the phase of the primary coil voltage extracted by this voltage feedback circuit 31, and a "saw" signal from this oscillation circuit 32. A pulse width modulation circuit (P
WM) 33, a base drive circuit 34 that turns on and off the transistor 8 according to the output pulse of the pulse width modulation circuit 33, a current feedback port that extracts the operating current flowing between 'am1 and the rectifier circuit 5; circuit 35, an output setting circuit 36 that outputs an output setting signal of a predetermined voltage level according to the value of the operating current extracted by this current feedback circuit 35, a command from the microcomputer 30, etc., and turning on and off of the base drive circuit 34. A frequency detection circuit 31 detects the output frequency of the inverter circuit based on the drive cycle, and when the detected frequency of this frequency detection circuit 37 exceeds a predetermined value based on a command from the microcomputer 30, the output of the output setting circuit 36 is oscillated to zero level. It consists of a stop circuit 38.

Next, the operation in the above configuration will be explained.

Place the food to be cooked in a heating chamber (not shown), and press the operating section 2.
1 to set the desired heating output. And keyboard 2
When the cooking start operation is performed in step 1, the control section 20 turns on and off the transistor 8 at a predetermined period. That is,
The resonant circuit is excited, and an alternating current voltage of a predetermined frequency corresponding to the set heating output is output from the inverter circuit. As a result, the magnetron 12 operates to oscillate, and dielectric heating cooking using high frequency radio waves is performed.

During this cooking, the frequency detection circuit 37 detects the output frequency of the inverter circuit via the base drive circuit 34.

Further, the oscillation stop circuit 38 determines whether the frequency detected by the frequency detection circuit 37 is equal to or higher than a predetermined value.

Therefore, between the anode and cathode of the magnetron 12,
Alternatively, if the high voltage diode 11a is short-circuited, an excessive current flows through the transistor 8 of the inverter circuit and the regeneration diode 9, creating a dangerous situation. At this time, the frequency detection circuit 37 detects that the output frequency of the inverter circuit increases to a predetermined value or more, and in response, the oscillation stop circuit 37
8 sets the output of the output setting circuit 36 to zero level. That is, the transistor 8 is immediately stopped turning on and off, and the operation of the inverter circuit is stopped.

In this way, if a short circuit occurs between the anode and cathode of the magnetron 12 or a short circuit occurs in the high voltage diode 11a, this is detected and the operation of the inverter circuit is immediately stopped. Damage to the element can be prevented. In other words, it is possible to prevent short circuit failures from spreading to other parts.
Repair costs can be kept to a minimum. Moreover, since a short-circuit failure in the high voltage circuit on the secondary side of the high voltage transformer 6 is detected in the low voltage circuit on the primary side of the high voltage transformer 6, the safety of the detection means itself can be sufficiently ensured.

Note that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made without changing the gist.

[Effects of the Invention] As described above, according to the present invention, damage to elements in the inverter circuit can be prevented in the event of a short-circuit between the anode and cathode of a magnetron or a short-circuit of a high-voltage diode. We can provide cooking utensils.

[Brief explanation of drawings]

The drawing is a diagram showing the configuration of a control circuit in an embodiment of the present invention. 8...NPN transistor (switching element),
12... Magnetron, 20... Criminal Control Department, 30...
・Microcomputer, 37...frequency detection circuit,
38...Oscillation stop circuit.

Claims (1)

[Claims] An inverter circuit that converts AC power supply voltage to DC and then converts it to AC voltage of a predetermined frequency and outputs it, a magnetron to which the output of this inverter circuit is boosted and rectified and applied, and an output frequency of the inverter circuit. A cooking appliance characterized by comprising: a frequency detecting means for detecting a frequency; and a means for stopping the operation of the inverter circuit when the detected frequency of the frequency detecting means exceeds a predetermined value.