JP3195694B2 - Magnetron drive control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to drive control of a magnetron for a microwave oven by an inverter power supply.

[0002]

2. Description of the Related Art Conventionally, drive control of this type of magnetron by an inverter power supply detects a resonance current between a high voltage transformer 3 and a resonance capacitor 5 with a current transformer 6 as shown in FIG. The current is detected by the current transformer 11 and both current information on the primary side and the secondary side of the high voltage transformer 3 is input to the on-time control circuit 9 from the start of driving to the stop of the magnetron 1 through the secondary current detecting circuit 8 until the magnetron 1 is stopped. In this case, the ON time of the switching element 4 is controlled so that a predetermined magnetron output is obtained.

The current transformer 6 has also been used for detecting a surge current in the primary side resonance circuit of the high voltage transformer 3.

[0004]

In the above configuration, both the currents flowing through the primary side and the secondary side of the high voltage transformer 3 must be monitored, so that the circuit configuration becomes complicated and the cost increases. Was also the cause.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. In a magnetron drive control circuit for driving a magnetron by an inverter power supply including a switching element, a high-voltage transformer, a resonance capacitor, and the like, a high-voltage transformer is provided. A current transformer that detects the primary side resonance current, a primary current detection circuit that captures the output signal of the current transformer and outputs a signal related to the prevention of inverter power supply destruction based on the output signal, and detects the current flowing when the magnetron is on to the secondary current detection circuit, only captures the current transformer output while the secondary current detecting circuit is outputting an oN signal, the preparative
An on-time control circuit that outputs a signal related to the on-time of the switching element based on the amount of output that has been input, and a drive that controls the switching element by taking in both the output signal of the on-time control circuit and the output signal of the primary current detection circuit Circuit.

[0006]

With the above arrangement, the primary current detection circuit monitors whether or not the primary resonance current detected by the current transformer has exceeded a specified value, and, if the primary resonance current has exceeded the specified value, a drive circuit. , A signal for turning off the switching element is output, so that the operation of the inverter power supply is immediately stopped, and the switching element is prevented from being broken.

Further, the primary-side resonance current detected by the current transformer is output to the on-time control circuit only during the time when the on-current flows through the magnetron through the secondary current detection circuit. The on-time of the switching element is determined based on the feedback amount of the on-time of the switching element, and the determined on-time is output to the drive circuit, and the switching element is driven to control the inverter power supply so that a predetermined magnetron output is obtained.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a magnetron.
Reference numeral 2 denotes an inverter power supply for driving the magnetron 1 and includes a switching element 3, a high-voltage transformer 4, a resonance capacitor 5, and the like. Reference numeral 6 denotes a current transformer for detecting a primary-side resonance current of the high-voltage transformer 4. Reference numeral 7 denotes a primary current detection circuit which detects a peak value of a primary side resonance current detected by the current transformer 6 and controls destruction of the switching element 3 and the like of the inverter power supply 2. Reference numeral 8 denotes a secondary current detection circuit including a current detection resistor 8a for detecting a current flowing when the magnetron 1 is turned on, and a detection output switch 8b (photocoupler) for outputting a signal only when the current is flowing. . Reference numeral 9 denotes an on-time control circuit for controlling the on-time of the switching element 3 in order to take in the output of the current transformer 6 via the secondary current detection circuit 8 and drive the magnetron 1 stably. Reference numeral 10 denotes a drive circuit that receives the outputs of the primary current detection circuit 7 and the on-time control circuit 9 together and drives the switching element 3.

Next, the operation of this embodiment will be described.

A power supply (not shown) is turned on, and the magnetron 1 is turned on.
Of the switching element 3 driven by the drive circuit 10 according to the set output of the magnetron 1 on the primary side of the high voltage transformer 4.
Turns on and off. At this time, the primary winding of the high voltage transformer 4 and the resonance capacitor 5 resonate at several tens of kHz. The voltage generated in the primary winding of the high-voltage transformer 4 by this resonance is boosted by the secondary winding of the high-voltage transformer 4, and the magnetron 1 is driven via the half-wave voltage multiplier circuit.

During operation of the magnetron 1, the primary-side resonance current of the high-voltage transformer 4 is detected by the current transformer 6 and input to the primary current detection circuit 7.

The primary current detection circuit 7 keeps monitoring the primary side resonance current. If the peak value of the primary side resonance current exceeds a specified value due to some abnormal condition, it outputs this to the drive circuit 10. Drive circuit 10 receiving this signal
Stops the drive control so as to suppress the destruction of the switching element 3, stops the operation of the inverter power supply 2, and stops the drive of the magnetron 1.

On the other hand, the primary-side resonance current detected by the current transformer 6 is also input to the on-time control circuit 10 through the secondary current detection circuit 8.

The secondary current detecting circuit 8 is a magnetron 1
And outputs a signal only when the operation is on at several tens of kHz.

For example, when the magnetron 1 is operated for a long time, the temperature of the magnetron 1 increases, the voltage of the magnetron 1 decreases, the current flowing through the magnetron 1 decreases, and the output decreases (drift). At this time, since the time during which the magnetron 1 is on (the time during which the current flows) is reduced, the output signal of the secondary current detection circuit 8 is short, and the output signal from the current transformer 6 to the on-time control circuit 9 is Decrease. Accordingly, the on-time control circuit 9 which receives the input signal determines that the output is insufficient, determines the on-time of the switching element 3 so that the set output of the magnetron 1 is obtained, and outputs a signal to the drive circuit 10.

The drive circuit 10 to which this signal has been input drives the switching element 3 for the ON time determined based on the above-mentioned data to drive the inverter power supply 2 so that the set output of the magnetron 1 is accurately maintained. Under the control, a predetermined output of the magnetron 1 is obtained.

[0018]

As described above, according to the present invention, in a magnetron drive control circuit for driving a magnetron by an inverter power supply including a switching element, a high-voltage transformer, a resonance capacitor and the like, a current transformer for detecting a primary-side resonance current of the high-voltage transformer; A primary current detection circuit that captures the output signal of the current transformer and outputs a signal related to the prevention of inverter power supply destruction based on the output signal; a secondary current detection circuit that detects a current flowing when the magnetron is turned on; An on-time control circuit that captures the output of the current transformer only while the detection circuit is outputting the on-signal, and outputs a signal related to the on-time of the switching element based on the amount of the captured output; and an output of the on-time control circuit. Signal and the output signal of the primary current detection circuit. The primary current detection circuit monitors whether the primary-side resonance current detected by the current transformer exceeds a specified value, and determines whether the primary-side resonance current is specified. If the value is exceeded, a signal for turning off the switching element is output to the drive circuit, so that the operation of the inverter power supply is immediately stopped, the switching element is prevented from being destroyed, and the primary side detected by the current transformer is detected. The resonance current is output to the on-time control circuit only when the on-current flows through the magnetron through the secondary current detection circuit, and the on-time control circuit captures the output of the current transformer for the on-time of this magnetron
The ON time of the switching element is determined based on the amount of the received output, and the ON time is determined and output to the drive circuit. The switching element is driven to control the inverter power supply, so that a predetermined magnetron output is obtained.

As described above, the protection of the switching element and the high reliability of the magnetron can be obtained at low cost by using only the primary side current transformer without providing the secondary side current transformer of the high voltage transformer.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a magnetron drive control circuit showing one embodiment of the present invention.

FIG. 2 is a circuit diagram of a magnetron drive control circuit showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetron 2 Inverter power supply 3 Switching element 4 High voltage transformer 6 Current transformer 8 Secondary current detection circuit 8a Detection output switch (photocoupler)

Continuation of the front page (56) References JP-A-3-171587 (JP, A) JP-A-2-44685 (JP, A) JP-A-4-105492 (JP, U) (58) Fields surveyed (Int) .Cl. ⁷ , DB name) H05B 6/66-6/68

Claims (1)

(57) [Claims] 1. A magnetron drive control circuit for driving a magnetron (1) by an inverter power supply (2) comprising a switching element (3), a high-voltage transformer (4), a resonance capacitor (5) and the like. A) a current transformer (6) for detecting a primary side resonance current, and a primary current for taking in an output signal of the current transformer (6) and outputting a signal related to prevention of breakdown of the inverter power supply (2) based on the output signal. A detection circuit (7), a secondary current detection circuit (8) for detecting a current flowing when the magnetron (1) is turned on, and a current transformer only while the secondary current detection circuit (8) is outputting an ON signal. An on-time control circuit for receiving the output of (6) and outputting a signal relating to the on-time of the switching element (3) based on the amount of the captured output; (9) and on-time control circuit (9)
And a drive circuit (10) for controlling the switching element (3) by taking in both the output signal of the primary current detection circuit (7) and the output signal of the primary current detection circuit (7).