JPS59194379A - Drive circuit of magnetron - 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 The present invention relates to a drive circuit for a magnetron used as heating means in a microwave oven, and more specifically, it proposes a drive circuit that increases the stability of input power.

Figure 1 is the conventional! This is an abbreviation of the drive circuit for a magnetron using a resonance wave drive method. The commercial frequency power supply 10 has a rectifier circuit 11
The pulsating output is rectified at
7, a flywheel diode 18, a switching element 19 such as a gate turn-off thyristor, a switching control circuit 20, and the like. The low-pass filter serves to prevent high frequency noise on the inverter side from propagating to the commercial frequency power supply 100III.

The switching element 19 is repeatedly turned on and off by a high-frequency pulse signal output from the switching control circuit 20. When the switching element 19 turns from on to off, the energy stored in the choke coil 15 and the primary winding 16p of the step-up transformer 16 during the on period causes the choke coil 15, the primary winding 16p, and the resonant capacitor 17 to A resonant voltage is generated across the resonant capacitor 17, and this discharge current causes the secondary winding 16s of the step-up transformer 16 to
The capacitor 23 of the half-wave voltage doubler rectifier circuit connected to is charged.

The step-up transformer 1 is turned on and off by the switching element 19.
A high frequency high voltage is generated in the secondary winding 16s of 6.
□This high voltage is applied to the capacitor 23 and diode 21.
, is applied to a half-wave voltage doubler rectifier circuit consisting of a varistor 22, and its output is applied to a magnetron 24 to excite it. Note that the tertiary winding 1 of the step-up transformer 16
6t is a power source for the heater of the cathode of the magnetron 24.

The advantages of using such a high frequency drive system include that the transformer can be made smaller and lighter than the conventional low frequency glue cage transformer, and that the magnetron output can be adjusted according to the output frequency of the inverter. Problems such as these remained.

The switching control circuit 20 is a voltage dividing circuit 20a that detects the input voltage (or input current) of the inverter and outputs a signal at a level proportional to the input voltage.

It consists of a signal conversion circuit 20b that outputs a pulse signal having a time width corresponding to the output voltage of the voltage dividing circuit 20a, and a driving circuit 20c for the switching element 19. FIG. 2 shows the conversion characteristics of the signal conversion circuit 20b, where the input signal (
The relationship between the voltage or current on the output side of the rectifier circuit 11 or the input side of the inverter and the time width of the output pulse signal is linear.

That is, when the input power of the inverter increases (decreases), the time width of the output pulse signal output from the signal conversion circuit 20b is shortened (lengthened) accordingly, and the ON time of the switching element 19 is determined by this time width. is shortened (expanded) to suppress (increase) the input power to the inverter. Although the input power is supposed to be stabilized by such feedback control, in reality, the input power goes out of control and its fluctuation reaches 200 to 300 degrees. As a result, there have been problems such as destruction of the switching element and saturation of the step-up transformer, making it impossible to excite the magnetron as expected.

The inventors of the present application focused on the fact that the cause of this problem is caused by the power factor of the inverter and the load connected thereto, and came up with the present invention. In other words, the load power factor is not 100%, so depending on the voltage or current, the inverter input power cannot be detected correctly.
Feedback control resulting from this becomes insufficient.

The present invention uses both input current and input voltage signals, adjusts the phase of one or both of them, detects the input power by the product of both signals, and performs feedbank control using this detection signal. Specifically, it is an object of the present invention to provide a magnetron drive circuit that stabilizes input power.

EMBODIMENT OF THE INVENTION Hereinafter, the present invention will be specifically explained based on drawings showing embodiments.

FIG. 3 is a schematic circuit diagram of a magnetron drive circuit according to the present invention, in which a commercial frequency power source 10 is connected to a rectifier circuit 11, and its output is passed through a low-pass filter consisting of a capacitor 12, 14 and a coil 13 to an inverter. The high frequency high voltage of the secondary winding 16s of the step-up transformer 16 is applied to a half-wave voltage doubler rectifier circuit consisting of a capacitor 23, a diode 21 and a varistor 22, and this rectified output is applied to the magnetron 24. The inverter has a choke coil 15 and a primary winding 16p1 of the step-up transformer 16.
Switching elements 19 such as a resonant capacitor 17, a flywheel diode 18, and a gate turn-off thyristor
It also includes a switching control circuit 25 for controlling on/off of the switching element 19, and still uses the tertiary winding 16s of the step-up transformer 16 as a power source for the heater of the cathode of the magnetron 24. The circuit of the present invention is different from the one shown in FIG. 1 in the switching control circuit 25. That is, the voltage of the output line of the rectifier circuit 11, that is, the input voltage of the inverter, is taken out by the input circuit 25d and applied to the signal conversion circuit 25b via the phase adjustment circuit 25e. The input current is detected by Cr26, and this is input to the input circuit 25f.
The signal is supplied to the signal conversion circuit 25b via the phase adjustment circuit 25g. The signal conversion circuit 25b outputs a pulse signal having a time width that changes from short to long depending on the magnitude of the signal corresponding to the input power, which is the product of both human forces, and supplies this to the drive circuit 25c to convert the switching element. 19 is turned on and off.

One of the phase adjustment circuits 2.5e, '25g may be omitted.

FIG. 4 is a circuit diagram showing a specific configuration of the switching control circuit 25. As shown in FIG. The positive output line of the rectifier circuit 11 consists of two resistors connected in series, and is connected to the input circuit 25a, which has a capacitor connected in parallel to one resistor to blunt the waveform, and the connection point between the resistors. Rectifying circuit 11
In other words, it is applied to the multiplier 30 as a signal representing the input voltage of the inverter.

That is, in this embodiment, the phase adjustment circuit 25e is omitted.

On the other hand, the CT26 provided on the negative side output line of the rectifier circuit 11
The detected current, that is, the output current of the rectifier circuit 11 or the input current of the inverter, is supplied to the input input of the multiplier 30 via an input circuit 25f consisting of a current limiting resistor and a phase adjustment circuit 25g.

The phase adjustment circuit 25g is configured to perform a required amount of phase shift by selecting the capacitance value of a capacitor 27 connected in parallel to the feedback resistor of an amplifier circuit using an operational amplifier 74, and the phase shift is performed by one person. The output of the operational amplifier is given to the multiplier 30.

The multiplier 30 provided at the input stage of the signal conversion circuit 25b uses, for example, a general-purpose multiplier XR-2208 manufactured by EXAR.The external resistor 30a adjusts the offset, and the resistor 30b adjusts the multiplier of the internal operational amplifier. is determined, and a signal obtained by multiplying the product of the surface input by this multiplier is obtained at its output terminal.

The output of this multiplier 30 is applied to a single input terminal of an operational amplifier 42. The reference voltage applied to the voltage terminal of the operational amplifier 42 is determined by resistors 70.degree. 71 and 72 connected thereto. Therefore, the larger (or smaller) the input to the operational amplifier 42, the lower (or higher) the output signal v.
, 2 is often emitted. The output signal V4□ is applied to the terminal of the comparator 47 via the resistor 73. The power terminal of the comparator 47 is connected to an over-input limiting circuit consisting of a diode 38 and resistors 39 and 39 for protection. The comparator 47 determines the time width of the output pulse signal of the switching control circuit 25, or the time at which it is a Gino-Inbel signal. After charging, this charging voltage v4□ is applied to the single-power terminal of the combination valve 47, υ, and while the signal given to the single-power terminal is at a high level as well as the signal to the single-power terminal, a high level output is generated. emanate.

The output of this comparator 47 is connected to the NAND gate 43.
43 to its set input S to the R-S flip 70 tube consisting of 1. The Q output of the R-S flip-flop is given to the drive circuit 25c, and the residual output is sent to a capacitor through a parallel circuit of a resistor 44 and a capacitor 45. 41
The terminal of is applied to the base of the connected transistor 46. When this transistor 46 is turned on, the capacitor 4
1 will be discharged. On the other hand, the comparator 48 determines the time period during which the output pulse of the switching control circuit 25 is at a low level. be. And this comparator 48
The output of the R-87 lip-flop is such that its reset power R is applied to the R-87 lip-flop. The terminal of the capacitor 49 is grounded via a transistor 51, and the Q output of the R-S flip-flop is applied to its base.

Drive circuit 20 C-MO8I C52 for cu handle 77
, 53 at the input stage, and the output thereof passes through a surge prevention circuit 54 using a diode to transistors 55, 56°5.
given to an amplifier circuit consisting of 7.58, 59.60, etc.
The configuration is such that the amplified output is given to the switching element 19. The base input of the transistor 55 is C-coupled using a capacitor 61, and is designed to shorten the rise time of the input pulse signal (square wave) by 9 hours. A diode 62 and a resistor 63 are also provided for speeding up. Transistors 57, 58 and 59, 60 are connected to form a complementary circuit. The coil 64 connected to the intermediate node of the transistors 59 and 60 and the resistor 65 connected thereto are provided for current limiting.

In the switching control circuit 25 configured as described above, the output v of the multiplier 30 is proportional to the product of the input voltage and the phase-adjusted input current, and is a signal representing the input power of the inverter. Since this voltage V is applied to the single power terminal of the operational amplifier 42, the operational amplifier output ■4□ becomes lower level (or higher level) as V becomes larger (or smaller).The operational amplifier 4 obtained in this way
It is compared with the charging voltage of the capacitor 41 by a 2 output V, 2V comparator 47. While the operational amplifier 42 output ■4□ is higher than the charging voltage ■4 of the capacitor 41, the comparator 47 output, the reset human power R of the Tsukuri R-S flip-flop is at the noi level, its Q output is high level, and the σ output is Maintain the state at low level. As a result, the transistor 51 is turned on and the transistor 46 is turned off. Eventually V4. When becomes higher than ■4□, the output of the converter 47 falls to a low level, and the R-S flip-flop state is reversed, so that the Q output becomes a low level and the R output becomes a 1 level. Therefore, transistor 46 is turned on to discharge the charge in capacitor 41, while transistor 51 is turned off and charging of capacitor 49 is started. While the voltage of the comparator 48 is higher than the charging voltage of the capacitor 49, the output of the comparator 48, that is, the reset voltage of the R-S flip-flop, is at a high level, but as the charging of the capacitor 49 progresses, R eventually becomes a low level. As a result, the R-S flip-flop is inverted, and the Q output changes to a high level and the Q output changes to a low level. As can be understood from this operation, the high level time of the Q output of the R-87 lip-flop is short in response to the high or low input power of the inverter, that is, the low or high level of the output V4 of the operational amplifier 42.

As a result, control is performed to keep the inverter input power constant.

As described above, the magnetron drive circuit according to the present invention is
In a magnetron drive circuit designed to excite the magnetron using a high frequency voltage obtained from an inverter, the input voltage and input current of the inverter are detected and correlated with a signal obtained by changing the phase of one or both of them. Since it was designed to control the switching of the inverter, the input power is stable regardless of changes in the load, and fluctuations in the input power are kept within a few inches.

Along with this, we were also able to obtain the effect of eliminating the abnormal beat sounds that were previously observed.

[Brief explanation of drawings]

Fig. 1 is a schematic circuit diagram of a conventional high-frequency drive type magnetron drive circuit, Fig. 2 is a conversion characteristic diagram of a conventional inverter input and its switching control signal pulse width, and Fig. 3 is a schematic diagram of the circuit of the present invention. This circuit diagram, FIG. 4, is a circuit diagram of the main part thereof. 19... Switching element 24... Magnetron 25... Switching control circuit 25b... Signal conversion circuit 25c... Drive circuit 25e, 25g...
Phase adjustment circuit patent applicant Noboru Kono 386, patent attorney representing Sanyo Electric Co., Ltd.

Claims (1)

[Claims] 1. In a magnetron drive circuit designed to excite the magnetron using a high frequency voltage obtained from an inverter, detecting the input voltage and input current of the above-mentioned input;
A magnetron drive circuit characterized in that switching control of an inverter is performed in association with a signal obtained by changing the phase of one or both of these.