JPH0668996B2 - High frequency heating device - Google Patents

Description

TECHNICAL FIELD The present invention relates to improvement of a high-frequency heating device using a high-frequency inverter circuit as a power supply device.

<Prior Art> A conventional circuit example will be described with reference to FIG. The commercial frequency power source 1 is rectified and smoothed by a rectifying / smoothing circuit including a diode bridge 2, a choke coil 3 and a smoothing capacitor 4. The inverter circuit includes a high-voltage transformer 101, a resonance capacitor 9 connected in parallel with the primary coil 5 of the high-voltage transformer, a switching element 10, and a diode 11,
The switching element 10 is turned on and off by driving the drive circuit 103 by the output signal of the control circuit 102 to generate a high frequency output on the secondary side of the transformer 101. The high frequency output boosted by the secondary coil 6 of the transformer 101 is rectified by the capacitor 13 and the diode 14 and applied between the anode and cathode of the magnetron 12. The output of the tertiary winding 7 is a magnetron.
Applied to 12 filaments. In this way, the magnetron 12 oscillates and heats the object to be heated with high frequency. The conventional control circuit 102 includes a synchronization detection circuit 16 that extracts a synchronization signal from the voltage of the detection coil 8 of the transformer 101 by the movement of the comparator 15, and a triangular wave that oscillates in synchronization with the synchronization signal by the comparator 17 and an output setting variable resistor. The pulse control circuit 19 compares the output voltage of the device 18 and the ON time and outputs a pulse (ON signal) proportional to the output voltage of the output setting variable resistor 18.

<Problems to be Solved by the Invention> Generally, the capacity of the smoothing capacitor 4 is selected small, and the voltage V _DC of the _DC power supply has a pulsating current as shown in FIG. 4 (a). On the other hand, no current flows in the magnetron 12 below the operation start voltage. Therefore, during the period when the power supply voltage V _DC is lower than the operation start voltage, no current flows in the magnetron, and its current waveform I _MG is the fourth.
As shown in FIG. 6B, the peak value was large. If the peak value of the magnetron current is large, there is a problem that the magnetron 12 causes a moding phenomenon.

Further, the voltage generated by the transformer also has a large peak value, and both the switching element 10 and the transformer 101 have to have a large withstand voltage, which is expensive.

The present invention has been made in view of such problems,
An object of the present invention is to provide a high-frequency heating device of low cost and high reliability by suppressing the current of the magnetron to a predetermined value or less and obtaining a stable operating state of the magnetron.

<Means for Solving Problems> The configuration of the present invention will be described with reference to FIG. 1 corresponding to the embodiment.

Output setting means 117 for setting the output of the high-frequency heating device,
A register 115 whose count number is set based on the output setting of the means 117, a voltage detecting means 104 for detecting the output voltage of the step-up transformer 101, and a current detecting means 105 for detecting the secondary coil current of the magnetron or step-up transformer. The output values of the voltage detection means 104 and the current detection means 105 are compared with the respective reference values, and when both output values are less than the reference value, the counter number of the register 115 is increased and one of the output values becomes the reference value. Count number increasing / decreasing means (106, 107, 118, 112, 110) for decreasing the count number when the value is greater than or equal to the value, and a counter for counting the reference clock pulse of the increased or decreased count number.
109 and drive control means (114, 103) for controlling the ON time of the switching element 10 by the output of the counter 109.

Further, since a small decrease in the number of counts cannot cope with a sudden voltage increase such as during a magnetron moding phenomenon, an abnormal high voltage detection means is provided and a predetermined time of the counter 109 is detected when the abnormal high voltage is detected. The count number is cleared so that the switching element 10 is turned off.

<Operation> The ON time of the switching element 10 is controlled by the output setting means 11
Based on the count number set by 7, the count number is increased when each output value of the voltage detection means 104 and the current detection means 105 is less than each reference value, and the count number is increased when one of the output values is greater than or equal to the reference value. Is reduced.

That is, since the digital control is performed based on the count number set by the output setting means 117, stable operation control in which the moding phenomenon is unlikely to occur is performed.

Further, by controlling the voltage generated in the step-up transformer 101 to be less than a predetermined value, the switching element 10 and the step-up transformer are
The withstand voltage of 101 can be lowered and the cost can be reduced.

<Example> An example of the present invention will be described below.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. The same parts as those of the conventional circuit shown in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted. FIG. 2 is an operation waveform diagram of the main part in FIG. In FIG. 1, when the switching element 10 is turned on and off by the output of the control circuit as shown in FIG. 2 (a), the resonance of the primary coil 5 of the transformer 101 and the resonance capacitor 9 causes the transformer 101 to be shown in FIG. Generate a voltage like b). This voltage is detected by the detection coil 8.

Reference numeral 111 denotes a synchronization detection circuit, which shapes the detection voltage of the transformer 101 with a diode clamp and a buffer, detects a falling edge, and generates a synchronization pulse shown in FIG. 2 (d). Reference numeral 109 is a counter for counting the ON time, which is composed of a down counter, sets the value of the register (A) 110 by a load signal, counts the clock of the reference clock pulse generation circuit 108, and when the set value becomes 0. The borrow signal is output, the flip-flop 114 is reset, and the output signal is turned off. Then, the above operation is repeated based on the generation of the synchronization pulse, and ON-OFF of the ON signal is repeated. Reference numeral 105 denotes an anode current detecting means, which connects a resistor 15 in series with the secondary winding 6 of the transformer 101 to take out the voltage drop thereof. The current waveform is shown in FIG. The shaded area in the figure is the anode current of the magnetron 12. The comparator 106 compares the voltage of the detection coil 8 with the reference voltage V ₁ and detects that the voltage generated by the transformer 101 is an overvoltage equal to or higher than the reference value. The comparator 107 compares the output of the current detection means 105 with the reference voltage V ₂ and detects an overcurrent equal to or higher than the reference value. When these comparators 106 and 107 detect an overvoltage or an overcurrent, the output becomes H, the output of the NOR circuit 118 becomes L, and the up / down counter of the register (A) 110 is set to the down count. Reference numeral 112 denotes a register (A) increasing / decreasing circuit, which outputs one clock pulse to the register (A) by a synchronization pulse and outputs a comparator.
The value of the register (A) 110 is increased or decreased by +1 or -1 according to the output of 106 or the comparator 107. After that, a counter 109 load pulse is output and the value of the register (A) 110 is set in the counter 109. Reference numeral 115 is a register (B) in which a count value corresponding to the ON time of the switching element 10 according to the set output set by the output setting means 117 is set. The register (A) 110 sets the count value of the register (B) 115 and increases / decreases the circuit 112.
The count value is increased or decreased by. However, register (A)
The count value of 110 is the maximum value of the count value of the register (B) 115 and is prohibited from further increasing. In this way, the ON time of the switch element 10 is registered in the register (B).
Determined based on the count value of 115, the power supply voltage V _DC
When the voltage becomes high and overvoltage or overcurrent is detected, the ON time is shortened and feedback control is performed so that the voltage and current fall below a specified value. FIG. 2 (e) is a current I _MG waveform diagram of the magnetron under the control of the present invention.

Since the ON time is increased / decreased step by step, it is not possible to deal with abnormal voltage due to the magnetron's moding phenomenon. Therefore, the abnormal voltage is detected by the comparator 113 and the ACL circuit 116 is activated for a predetermined time to turn off the output.
The components such as the switching element 10 are protected.

After that, the ACL circuit 116 is turned off and restarted.

<Effects of the Invention> Since the high-frequency heating apparatus of the present invention has the above-described configuration, the control circuit is digitized by the control circuit.
Since the secondary winding voltage and the magnetron current can be suppressed to a predetermined value or less and the peak current can be lowered, the operation of the magnetron can be stabilized, the withstand voltage of the transformer and the switching element can be lowered, and the cost can be reduced. Moreover, since the control circuit is processed by the comparator instead of using an expensive A / D comparator for digitizing the current and voltage, it can be easily digitized at low cost and by digitizing the circuit. No adjustment required LS
By adopting I, a significant cost reduction can be achieved.

Moreover, since the count number of the register is increased / decreased step by step by the count number increasing / decreasing means based on the output of the comparing means, even if the output setting by the output setting means is changed abruptly, It is possible to surely prevent the abnormal phenomenon of the magnetron due to the rapid increase of the output without the abrupt change of the on-time of the switching element by gradually increasing or decreasing by one step.

Furthermore, even if noise is superimposed on the detection output of the current detection means,
Because this noise causes the register count to change gradually without abruptly changing, the change in register count due to noise is minimized and output change can be minimized, resulting in destruction of switching elements. Can be prevented.

Then, since the increase / decrease of the register count number by the count number increase / decrease unit cannot deal with a sudden voltage increase such as when the magnetron modifies, the abnormal high voltage detection unit clears the count number of the counter. By turning off the switching element for a predetermined time,
It is possible to reliably prevent damage to the magnetron and the switching element due to an abnormal state.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram of a main portion of FIG. 1, FIG. 3 is an electric circuit diagram of a conventional example,
4 (a) and 4 (b) are waveform diagrams of a power supply voltage and a magnetron current I _MG wave in a commercial power supply cycle. Reference numeral 10: switching element, 12: magnetron, 101: step-up transformer, 104: voltage detection means, 105: current detection means, 106, 107,
118, 112, 110: count number increasing / decreasing means, 108: reference clock pulse generating circuit, 109: counter, 113: abnormal high voltage detecting means, 114, 103: drive control means, 115: register, 116: ACL circuit, 117: output setting means.

Claims (1)

[Claims] 1. A rectifying / smoothing circuit for rectifying / smoothing a commercial power source to produce a DC power source, a step-up transformer for driving a magnetron,
An inverter circuit composed of a capacitor, a diode, a switching element, etc., a magnetron drive circuit for driving a magnetron with a high-frequency power source made by the inverter circuit, and a control circuit for ON / OFF controlling the switching element of the inverter circuit are provided. In the high-frequency heating device provided, output setting means, a register for setting a count number based on the output of the means, voltage detecting means for detecting the output voltage of the step-up transformer, and a secondary winding of a magnetron or step-up transformer. The output values of the current detection means for detecting the line current and the voltage detection means and the current detection means are compared with the respective reference values, and when both output values are less than the reference value, the count number of the register is increased by one step, When either output value is above the reference value, the count number is decreased by one step. Count number increasing / decreasing means, a counter for counting the reference clock pulse of the increased / decreased count number, drive control means for controlling the ON time of the switching element by the output of the counter, and the voltage detecting means for detecting an abnormal high voltage. The high frequency heating device further comprises: an abnormal high pressure detecting means for turning off the switching element by clearing the count number of the counter for a predetermined time.