JPH04111192U - High frequency heating device - Google Patents

Abstract

(57) [Summary] [Purpose] To realize an inverter circuit with excellent safety and reliability. [Configuration] A current detection circuit 15 that detects the anode current value flowing through the magnetron, converts it into a digital value, and transmits it to the control circuit 9; and a current detection circuit 15 that transmits the digital value converted by this current detection circuit to the microcomputer 13. Communication circuit 1
6 is provided, and if the input value input through this communication circuit does not reach the specified value after a specified time has elapsed from the start of cooking, the microcomputer determines that the circuit is abnormal and stops the operation of the inverter.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention is a high-frequency heating device that drives a magnetron using an inverter circuit. It is related to

0002

[Conventional technology]

It rectifies the commercial AC power supply and sets it by the customer by turning the switching element on and off. An inverter circuit that converts the high frequency output into AC power at a frequency (several tens of kHz) This inverter circuit is equipped with a high-frequency generator that supplies power to the magnetron. Conventionally, abnormalities in thermal equipment are detected using the circuit configuration shown in Figure 4. Ta.

0003 In other words, to explain Fig. 4, the commercial AC power supply 1 has a diode bridge 2, a choke A rectification and smoothing circuit consisting of a coil 3 and a smoothing capacitor 4 performs rectification and smoothing. stomach The inverter circuit is connected in parallel to the primary winding 5a of the magnetron drive transformer 5. a resonant capacitor 6, and a semiconductor switch connected in series with the primary winding 5a. It is composed of a control circuit element 7 and a diode 8, and the semiconductor Turns on/off switching element 7 to generate high frequency output on the secondary side of transformer 5 let The high frequency voltage generated in the secondary winding 5b of the transformer 5 is connected to the capacitor 10 and The voltage is rectified and boosted by a voltage doubler rectifier circuit composed of diodes 11. is applied to pin 12. This causes the magnetron 12 to oscillate microwaves. The microcomputer 13 receives a start signal P that instructs the control circuit 9 to operate/stop. and a high frequency output as a data signal D, and the control circuit 9 uses these as an inverter. Controls the data circuit.

0004 In the abnormality detection circuit 18, a circuit inserted into the secondary circuit is used to detect overcurrent on the secondary side. The voltage generated across the resistor 19 and the reference voltage Vs are compared by a comparator C, and the circuit When an abnormality occurs and overcurrent flows to the secondary side, the voltage generated across the resistor 19 becomes the reference voltage Vs. As a result, the output Vo of the comparator C is transmitted to the control circuit 9, and the switch This is to stop the operation of the switching element 7.

[0005]

[Problem that the idea aims to solve]

However, this conventional example is for detecting excessive current exceeding a certain value; Depending on the failure of the control circuit, the inverter circuit may not operate at all, or the magnetron may However, due to poor airtightness or deterioration, a moding phenomenon occurs and almost no current flows. In the opposite case, this cannot be detected. Furthermore, the secondary winding of the transformer If the wire is short-circuited, no anode current is supplied to the magnetron, so As this is not detected, the rare short section of the transformer heats up abnormally, causing smoke and ignition. This may lead to dangerous modes such as

[0006]

[Means to solve the problem]

A current that detects the anode current value flowing through the magnetron and converts it into a digital value. The detection circuit and this digital current value are transmitted to the microcomputer as input values. A communication circuit will be provided. The microcomputer performs this process after a specified time from the start of cooking. Read the input value, and if it does not reach the specified value, a circuit abnormality has occurred. The operation of the inverter circuit is stopped as follows.

[0007]

[Effect]

To determine whether the inverter circuit is operating at the set high frequency output. In order to The magnetron is fed back to the microcomputer and uses the time when cooking starts as a reference. When the microcomputer is estimated to have transitioned to steady operation, the microcomputer Read the checked input current value, and if this value does not reach the specified value, the input current will be reset normally. It is determined that the inverter is not operating, and the operation of the inverter circuit is stopped.

[0008]

【Example】

An embodiment of the present invention will be described below.

[0009] FIG. 1 is a circuit diagram showing an embodiment of the present invention.

0010 The same parts as in the circuit diagram of the conventional example shown in FIG. 4 are denoted by the same reference numerals.

[0011] Now, the microcomputer 13 informs the control circuit 9 of the inverter circuit. Outputs start signal P to instruct operation/stop and also sets high frequency output The output value is output as a data signal DATA.

0012 On the other hand, the anode current flowing through the magnetron 12 is detected by the current transformer 14. This is input to the current detection circuit 15. Here, the rectified and smoothed voltage V in is converted into 6-bit parallel data Din by an A/D converter, and this is converted into 6-bit parallel data Din. is fed back as input data to the comparison section 9a of the control circuit 9 via the switch. There is. The comparator 9a compares this fed-back input data Din with the microcontroller. Compare the setting data DATA sent from the computer 13 and use the results. It is transmitted to the pulse width control section 9b. This feedback comparison results The pulse width control section 9b controls the pulse width of the pulse signal P that drives the switching element 7. control and adjust the output.

[0013] The communication circuit 16 is an input fed back from the current detection circuit 15 to the control circuit 9. Take in the data Din and use the selector 16a, binary counter 16b, etc. is converted into 6-bit serial data SDin, and the clock signal is converted to 6-bit serial data SDin as shown in Figure 2. Using CLK, the microcomputer 13 uses the fall of the transmission start signal S as a reference. Send to. This data changes as shown in Figure 3 depending on the set high frequency output. The temperature is almost zero immediately after the start of cooking, but the magnetron 12 starts oscillating and the anode When the current starts flowing, it gradually increases and reaches a steady value.

[0014] This microcomputer 13 is activated after a specified time ts has elapsed from the start of cooking. After Netron starts oscillating, this input data SDin is taken in and specified data D Compare with s. This specified time ts is necessary for the magnetron to reach steady operation. Determine the required rise time by taking into account its change over time. In addition, regulatory data Ds is the input data input at the minimum high frequency output that can be set as shown in Figure 3. Set it to a value that is sufficiently smaller than the above value. The microcomputer 13 receives input data SDin If SDin does not reach Ds, it is due to circuit abnormality. It is determined that the magnetron is not operating normally, and the start signal P to the control circuit 9 is turned off. In this case, the operation of the inverter circuit can be stopped.

[0015]

[Effect of the idea]

As mentioned above, according to the present invention, magnets, which could not be detected conventionally, It is possible to detect oscillation failures caused by Ron moding and circuit failures, improving safety. Furthermore, an inverter circuit with excellent reliability can be realized. Also, examples If the control circuit is composed of digital circuits as in This invention can be realized at low cost by using We can provide an excellent high-frequency heating device.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a signal diagram of the communication section.

FIG. 3 is a diagram showing changes in input data to the microcomputer.

FIG. 4 is a circuit diagram of a conventional example.

[Explanation of symbols]

9 Control circuit 13 Microcomputer 15 Current detection circuit 16 Communication circuit

Claims (1)

[Scope of utility model registration request] [Claim 1] A rectifier and smoothing circuit that rectifies and smoothes a commercial power supply to produce a DC power supply, a transformer, a capacitor, a diode,
an inverter circuit composed of switching elements;
A control circuit that controls on/off switching elements of the inverter circuit according to the set high frequency output, a magnetron driven by the high frequency power supply generated by the inverter circuit, and a microcontroller that transmits the set high frequency output to the control circuit. A computer comprising a computer and a current detection circuit that detects the current value of the anode current flowing through the magnetron, converts it into a digital value, and transmits it to the control circuit, wherein the digital value converted by the current detection circuit is A communication circuit is provided to transmit the value to the microcomputer, and if the input value input through the communication circuit is less than the specified value after a specified time has elapsed from the start of cooking, the microcomputer determines that it is abnormal and the inverter circuit is activated. A high-frequency heating device characterized by stopping its operation.