JPH0785963A - Magnetron drive control circuit - Google Patents

Abstract

PURPOSE:To protect a switching element at a low cast and equip a magnetron with high reliability by furnishing a primary and a secondary current sensing circuit, an on-time control circuit, and a drive circuit, CONSTITUTION:While a magnetron 1 is in service, the primary side resonance current in a high voltage transformer 4 is sensed by a current transformer 6 and fed to a primary current sensing circuit 7, and also is entered into an on-time control circuit 9 via a secondary current sensing circuit 8. When the primary side resonance current sensed by the transformer 6 has exceeded the specified value, the primary current sensing circuit 7 gives an appropriate signal to a drive circuit 10. This signal turns on a switching element 3, and the power supply of an inverter stops operating immediately so that the element 3 is prevented from destruction. The secondary current sensing circuit 8 feeds current to the on-time control circuit 9 for a period of time in which the on-current has flowed, and the circuit 9 determines the (on-time of the element 3 on the basis of the feedback amount during on-time, and the resultant is fed to the drive circuit 10 so that the switching element 3 is driven for controlling the inverter power supply 2, and thus the specified output is obtained.

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 by an inverter power supply of this type of magnetron 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 information of both the primary side and the secondary side of the high voltage transformer 3 detected by the current transformer 11 is input to the on-time control circuit 9 from the start of the driving of the magnetron 1 to the stop thereof by passing through the secondary current detection circuit 8. However, the on time of the switching element 4 is controlled so that a predetermined magnetron output can be 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-mentioned configuration, since both currents flowing to the primary side and the secondary side of the high voltage transformer 3 must be monitored, the circuit configuration becomes complicated and the cost increases. It was also the cause of

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and in a magnetron drive control circuit for driving a magnetron by an inverter power source including a switching element, a high voltage transformer, a resonance capacitor, etc. The current transformer that detects the primary side resonance current, the primary current detection circuit that captures the output signal of the current transformer and outputs the signal related to the destruction prevention of the inverter power supply based on the output signal, and the current that flows when the magnetron is on ON current control circuit that takes in the output of the current transformer only while the secondary current detection circuit outputs the ON signal, and outputs a signal related to the ON time of the switching element based on this feedback amount. Circuit and the output signal of the on-time control circuit And a drive circuit for controlling the switching elements together takes in the output signal of the primary current detecting circuit when.

[0006]

With the above structure, the primary current detection circuit monitors whether or not the primary-side resonance current detected by the current transformer exceeds the specified value, and when the primary-side resonance current exceeds the specified value, the drive circuit. Since the signal for turning off the switching element is output to the inverter, the operation of the inverter power supply is immediately stopped and the switching element is protected from destruction.

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

[0008]

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a magnetron.
Reference numeral 2 denotes an inverter power supply for driving the magnetron 1, which is composed of a switching element 3, a high voltage transformer 4, a resonance capacitor 5, and the like. Reference numeral 6 is a current transformer for detecting the primary side resonance current of the high voltage transformer 4. A primary current detection circuit 7 detects the peak value of the primary side resonance current detected by the current transformer 6 and controls the destruction prevention of the switching element 3 and the like of the inverter power supply 2. Reference numeral 8 is a secondary current detection circuit composed of a current detection resistor 8a for detecting a current flowing when the magnetron 1 is 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 that takes in the output of the current transformer 6 via the secondary current detection circuit 8 and controls the on-time of the switching element 3 to stably drive the magnetron 1. Reference numeral 10 is a drive circuit for taking in the outputs of the primary current detection circuit 7 and the on-time control circuit 9 together and driving the switching element 3.

Next, the operation of this embodiment will be described.

A magnetron 1 is turned on by turning on a power source (not shown).
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 2 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 doubler circuit.

While the magnetron 1 is in operation, 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 continues to monitor the primary side resonance current, and outputs it to the drive circuit 10 when the peak value of the primary side resonance current exceeds a specified value under some abnormal condition. Drive circuit 10 that receives 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 via the secondary current detection circuit 8.

The secondary current detection circuit 8 is a magnetron 1
It detects the current that flows in and outputs a signal only when it is on and operating at several tens of kHz.

For example, when the magnetron 1 is operated for a long time, the temperature of the magnetron 1 rises, the voltage of the magnetron 1 decreases, the current flowing through the magnetron 1 decreases, and the output decreases (drifts). At this time, the time during which the magnetron 1 is on (the time during which the current flows) has decreased, so the output signal of the secondary current detection circuit 8 becomes short and the output signal from the current transformer 6 to the on-time control circuit 9 becomes Decrease. Therefore, the on-time control circuit 9 that has received this input determines that the output is insufficient and 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 is input drives the switching element 3 with the ON time determined based on the above-described data so that the set output of the magnetron 1 is accurately maintained, and drives the inverter power supply 2. By controlling, the 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, etc., a current transformer for detecting a primary side resonance current of the high voltage transformer, A primary current detection circuit that takes in the output signal of the current transformer and outputs a signal related to the destruction prevention of the inverter power supply based on the output signal, a secondary current detection circuit that detects the current that flows when the magnetron is on, and this secondary current The on-time control circuit that takes in 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 this feedback amount, and the output signal of the on-time control circuit and the primary Take both output signals of the current detection circuit Therefore, the primary current detection circuit monitors whether or not the primary side resonance current detected by the current transformer exceeds the specified value by providing a drive circuit for controlling the switching element, and the primary side resonance current is set to the specified value. When the voltage exceeds the limit, a signal for turning off the switching element is output to the drive circuit, so the operation of the inverter power supply stops immediately, the switching element is escaped from destruction, and the primary side resonance detected by the current transformer. The current is output to the on-time control circuit for the time when the on-current flows through the magnetron through the secondary current detection circuit, and the on-time control circuit determines the on-time of the switching element based on the amount of feedback of the on-time of this magnetron. Output to the drive circuit and drive the switching element to drive the inverter power supply. Gyoshi, given magnetron output is controlled so as to obtain.

As described above, the secondary side current transformer of the high voltage transformer is not provided and only the primary side current transformer is provided, so that the protection of the switching element and the high reliability of the magnetron can be obtained at low cost.

[Brief description of drawings]

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

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

[Explanation 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)

Claims (2)

[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), etc. A current transformer (6) for detecting a primary side resonance current, and a primary current detection circuit (7) for taking in an output signal of the current transformer (6) and outputting a signal for preventing destruction of an inverter power supply (2) based on the output signal. ), A secondary current detection circuit (8) for detecting a current flowing when the magnetron (1) is turned on, and a secondary current detection circuit (8) for the current transformer (6) only while the secondary current detection circuit (8) outputs an ON signal. An on-time control circuit (which takes in the output and outputs a signal related to the on-time of the switching element (3) based on this feedback amount ( 9) and a drive circuit (10) for controlling the switching element (3) by taking in both the output signal of the on-time control circuit (9) and the output signal of the primary current detection circuit (7). Magnetron drive control circuit. 2. The magnetron drive control circuit according to claim 1, wherein the secondary current detection circuit (8) performs a duty control for outputting an ON signal only while the magnetron (1) is ON. .