JPH01313888A - High-frequency heating device - Google Patents

Abstract

PURPOSE:To enable obtaining excellent safety and high reliability by stopping the operation of an inverter power supply when a difference between a reference anode current value computed on the basis of the output set value of a magnetron and a current value inputted to a control circuit is equal to or above the predetermined value. CONSTITUTION:There are provided a current detecting circuit 8 for detecting the anode current Ib of a magnetron 3 and a voltage detecting circuit for detecting power supply voltage supplied to an inverter circuit D. Current and voltage values detected with both of the aforesaid circuits are fed back to a control circuit 6 for controlling the operation of a switching element 1. In the control circuit 6, when the device in the title is operated on an output value selected by a user when the power supply voltage is equal to an input value, the value of an anode current flowing to the magnetron 5 is computed and compared with an inputted anode current value. When a difference between both values is equal to or above the predetermined value, the circuit 6 judges that a circuit is abnormal and interrupts the operation of the switching element 1, thereby stopping a heating process. According to the aforesaid construction, it becomes possible to obtain excellent safety and reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a high-frequency heating device in which a magnetron is driven by an inverter circuit.

In particular, the abnormality detection function of the inverter circuit has been improved.

(Prior art) This inverter is equipped with an inverter circuit that rectifies commercial AC power supply voltage and converts it into AC power at a frequency (several tens of K11z) according to the magnetron output set by the customer by turning on and off switching elements. In a high-frequency heating device in which power is supplied to a magnetron by a circuit, a method as shown in FIG. 3 has conventionally been used as means for detecting abnormal operation of two circuits.

In FIG. 3, the power converted into an alternating current of several tens of K11z by turning the switching element 1 on and off is as follows.

After being boosted by the high-voltage transformer 2, the voltage is supplied to the magnetron 3, and the voltage generated across the resistor 4 inserted in the secondary circuit (high-voltage circuit) of the high-voltage transformer 2 is compared with the reference voltage Vs in the comparator circuit 5. .

When an abnormality occurs in the circuit and excessive current flows to the secondary side, the voltage generated across resistor 4 exceeds the reference voltage Vs.

As a result, the output VO of the comparison circuit 5 is inverted with respect to the normal state, and this is fed back to the control circuit 6 to stop the operation of the switching element 1.

(Problem to be solved by the invention) However, this method is for detecting excessive current, and instead of having a single magnetron output, it is a variable-output high-frequency heating system that allows customers to freely select the magnetron output according to their cooking needs. Even if the device operates at an output value different from the selected output value due to an abnormality in one circuit, this cannot be detected, and not only will cooking fail, but in the worst case, the output value will far exceed the selected value. Because it heats up, there is a risk that the food will become dangerous, such as causing the food to emit smoke.

(Means for solving the problem) Whether or not the inverter circuit is operating at the selected output value can be determined by measuring the anode current flowing through the magnetron. Since it is conceivable that it differs depending on the power supply voltage applied to the inverter circuit, it is necessary to make a judgment based on both. Both values are detected and the predicted magnetron anode current value is calculated when operating at the selected output value at the detected power supply voltage value.

It is detected whether the inverter circuit is operating according to the selected output by determining whether the actually detected current value does not deviate.

(Function) A current detection circuit that detects the anode current of the magnetron and a voltage detection circuit that also detects the power supply voltage supplied to the inverter circuit are provided, and the current value detected by these two circuits,
The voltage value is fed back to a control circuit that controls the operation of the switching element. The control circuit calculates the anode current value that should flow through the magnetron when operating at the output value selected by the customer at the input power supply voltage value, and compares this value with the input anode current value. hand.

If the difference exceeds a predetermined value, it is assumed that there is an abnormality in the circuit, the operation of the switching element is stopped, and heating is stopped.

(Example) FIG. 1 shows an example of the present invention. 1 is a switching element, 2 is a high-voltage transformer, 3 is a magnetron, and 6 is a control circuit, the center of which is a microcomputer Taro a with a built-in A/D conversion function. 7 is a magnetron output setting circuit, and the output value p set from this is the signal S (
p) is inputted to the drive circuit 6b and the microcomputer a. 8 is a current detection circuit, which is composed of a rectifying and smoothing circuit to average the anode current of the magnetron 3, and detects the voltage generated in the resistor 4 when the anode current Ib flows by using a large-capacity electrolytic capacitor. The voltage is averaged and converted into a DC voltage V (Ib), which is input to the A/D conversion board of the microcombi 6a. Further, reference numeral 9 denotes a voltage detection circuit, which is incorporated in the AC circuit section in front of the rectifier section in order to detect the power supply voltage supplied to the inverter circuit, and includes a transformer 9a and a rectifier smoothing circuit 9b.
It consists of The commercial AC power supply voltage V is transferred to the transformer 9a.
, and the rectifying and smoothing circuit 9b also drops the DC voltage V.
(v) and convert it to A/
It is input to the D conversion port. microcomputer 6
The memory of a contains a reference value Ibs (v,
p) is stored.

FIG. 3 shows the processing flow within the microcomputer ea in this embodiment.

The microcomputer 6a simultaneously A/D converts the signal V (v) from the voltage detection circuit 9 and the signal V (Ib) from the current detection circuit 8, and performs each predetermined operation on the converted values. Measured values vd and Ibd of the power supply voltage and the average anode current of the magnetron are calculated. Furthermore, from the calculated power supply voltage value vd and the output value p set by the customer, a reference value Ib5 (
vd, p). And this reference value Ib5(v
Actual measured value I obtained from d, p) and V(Ib)
It is determined whether the absolute value of the difference from bd satisfies the following equation.

l Ibd - Ibs (vd, p) l≦ΔI where Δ■ is a constant determined in consideration of measurement error and calculation error.

If the difference is larger than ΔI, it is determined that there is an abnormality, that is, the inverter circuit is not operating at the set output value, and the microcomputer Taro a turns on and off the switching element 1 in the drive circuit 6b. An off signal is output to the control signal C output to the switch 1 to stop the operation of the switching element 1.

This operation of checking the inverter circuit current by the microcomputer is to detect any abnormalities in the two circuits at an early stage.

(Effects of the Invention) As described above, according to the present invention, erroneous output operations that could not be detected conventionally can be detected.

It is possible to realize an inverter circuit type high-frequency heating device with excellent safety and reliability.

[Brief explanation of the drawing]

FIG. 1 is a control circuit diagram of this embodiment, and FIG. 2 is an explanatory diagram showing processing inside a microcomputer in this embodiment.
FIG. 3 is a control circuit diagram of a conventional example. 1°° switching element, 2°° high voltage transformer, 3
...Magnetron, 4...Resistor for current detection, 6...
- Comparison circuit, 6... Control circuit, 6a... Microcomputer. 6b... Drive circuit, 7... Output setting circuit, 8...
Current detection circuit, 9... Voltage detection circuit, 9a...
Transformer, 9b... rectifier smoothing circuit.

Claims (1)

[Claims] an inverter power supply that rectifies a commercial AC power supply voltage and converts it into AC power of an arbitrary frequency to drive the magnetron; a control circuit that controls the frequency according to a set output value of the magnetron; Consisting of a voltage detection circuit that detects the commercial AC power supply voltage and inputs this voltage value to the control circuit, and a current detection circuit that detects the anode current flowing through the magnetron and inputs this current value to the control circuit as well. The difference between the reference anode current value calculated based on the voltage value input to the control circuit and the output setting value of the magnetron and the current value input to the control circuit is a predetermined value. A high-frequency heating device characterized in that the control circuit stops the operation of the inverter power supply when the above condition occurs.