JPH044593A - Magnetron driving device - Google Patents

Abstract

PURPOSE:To prevent generation of abnormal sounds when oscillation is started, by feeding the On power to a switching element from a power supply in conformity to signal given by a signal output part. CONSTITUTION:When power is put on, a voltage full-wave rectified by a full- wave rectifier 1 is impressed on the collector of a switching element 5. At that time, the terminal voltage VC of a capacitor 20 becomes higher than this collector voltage VT, and a diode 15 remains off, so that the capacitor 20 is charged via a resistance 17. The terminal voltage VC of the capacitor 20 rises accordingly to cause by and by a transistor 21 to be turned on, and thereby a transistor 24 is also turned on, when the On voltage will be impressed on the base of the switching element 5 to cause it to be turned on. As a result, self-excited oscillation is started. This allows continued oscillation even though the oscillation is started at a lower supply voltage, and generation of abnormal sounds at the starting time of oscillation is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a magnetron drive device that drives a magnetron using an output from an inverter circuit.

(b) Conventional technology A conventional technique will be explained based on FIGS. 1 and 2.

FIG. 1 is a circuit diagram of a self-excited voltage resonance type switching power supply, and FIG. 2 is an operating waveform diagram thereof. 1 is a full wave rectifier, 2 is a choke coil connected to the full wave rectifier l, 3
is a smoothing capacitor connected to the choke coil 2 and the output terminal of the full-wave rectifier 1, 4 is a resonant capacitor, and 5 is a switching element.The resonant capacitor 4 and the switching element 5 are connected in series, and in parallel with this series circuit. A smoothing capacitor 3 is connected. 6 is a transformer, and this transformer 6 has a primary winding 6 connected in parallel with the resonant capacitor 4.
a, a secondary winding 6b, and a base winding 6c. The base winding 6C has one end connected to the switching element 5.
The intermediate tap is connected to the output terminal of the full-wave rectifier 1 at the base of the rectifier. 7 is a magnetron connected to the secondary winding 6b of the transformer 6. 8 is a resistor, and 9 is a capacitor, which are connected in series between the output terminals of the full-wave rectifier 1.

10 is a diac connected to the base of switching element 5 and the connection point between resistor 8 and capacitor 9; 11 has a drain connected to the base of switching element 5 and a source connected to the other side of base winding 6C of transformer 6. It is an FET. 12 is a diode, and 13 is a Zener diode.

The anodes of these are connected to form a series circuit, and this series circuit is connected between the connection point of the resistor 8 and the capacitor 9 and the collector of the switching element 5. Starting circuit 26 with the above resistor 8, capacitor 9, diac 10, FET II, diode 12, and Zener diode 13
is configured. The operation of this circuit is as follows: Immediately after the power is turned on, capacitor 9 is charged through resistor 8, and its terminal voltage rises. Accordingly, the potential difference between the terminals of the diac 10 gradually increases. At this time, base winding 6
Since no voltage is generated at c, the switching element 5 is off. The potential difference between the terminals of the diac 10 is a predetermined value Vi(
When the voltage reaches 20 V to 40 V (generally 20 V to 40 V), the inductor 10 turns on and the discharge current of the capacitor 9 flows to the base of the switching element 5. As a result, the switching element 5 is turned on, and current flows through the primary winding 6a of the transformer 6. Then, an induced voltage is generated in the base winding 6c in the direction flowing to the base of the switching element 5, and the switching element 5 continues to be in the on state (period (A) in FIG. 2). When the current flowing through the primary winding 6a of the transformer 6 reaches a predetermined value, the control circuit 14 outputs an on signal to the FET II, sets the base of the switching element 5 to a negative voltage, and turns it off. At this time, charging and discharging of the resonant capacitor 4 starts, and 1
An oscillating current begins to flow into the next winding 6a. A voltage having a differential waveform of the current flowing through the primary winding 6a is induced in the base winding 6c. The voltage induced in the base winding 6c is shown in the period (b) of FIG. During this (b) period,
The current flowing through the primary winding 6a oscillates over time. A voltage with a differential waveform of this current appears at the base winding 6C. When the amount of change in the oscillating current is zero, that is, the negative current reaches its peak value, and the switching element 5 is connected to the Tatoki base winding 6C.
This becomes a voltage that turns on the switching element 5. Thereafter, this operation is repeated to achieve continuous oscillation.

(C) Problems to be Solved by the Invention In the conventional example described above, the trough of the pulsating current output from the full-wave rectifier 9#1 is several volts, and the base winding 6C has a sufficient voltage to turn on the switching element 5. is not obtained, the switching element 5 is not turned on and self-oscillation is stopped. Then, in order to start oscillation next time, a predetermined potential difference needs to be generated between both terminals of the diac 10. This potential difference occurs only after the power supply voltage becomes high to a certain extent.

Therefore, when oscillation starts, a large current is generated, resulting in abnormal noise.

(d) Means for Solving the Problem The means for solving the problem of the present invention is composed of a resonant capacitor, a switching element, a diode connected in antiparallel to the switching element, and a primary winding of a transformer. an inverter circuit, a magnetron connected to a secondary winding of the transformer, and a base winding electromagnetically coupled to the primary winding of the transformer, the base winding being connected to the switching element and connected to the switching element. The device that supplies an on signal to the switching element includes a voltage detection section that detects a terminal voltage of the switching element, a signal output section that outputs a signal when the voltage detection section detects that oscillation has stopped, and a signal that outputs an on signal to the switching element. and a power supply section that supplies power, and is configured such that on-power is supplied from the power supply section to the switching element in response to a signal from the signal output section.

(e) Operation If the peak value of the collector voltage of the switching element 5 is lower than the set value, on-power is supplied to the base of the switching element 5, so self-oscillation will continue to oscillate even when the power supply voltage becomes low. It is something to do.

(f) Examples An embodiment of the present invention will be described based on FIG.

Components having the same functions as those in FIG. 1 are given the same numbers as in FIG. 1, and their explanations will be omitted.

In place of the starting circuit 26 in FIG. 1, a power supply circuit 27
is used. In this circuit, the cathode of a diode 15 is connected to the collector of the switching element 5.
The anode of the resistor 16 is connected to one end of the resistor 16. A series circuit of resistors 17, 18, and 19 is connected to the power source for the control circuit, and a capacitor 20 is connected in parallel with this resistor 18, 19. The terminal voltage of this capacitor 20 is ■. shall be.

Further, the resistance value of the resistor 17 is selected to be smaller than the resistance value of the resistor 16.

The connection point between the resistors 18 and 19 is connected to the base of a transistor 21, and a series circuit of resistors 22 and 23 is connected between the collector of the transistor 21 and the control circuit power supply. The base of a transistor 24 is connected to the connection point between the resistors 22 and 23, the emitter of this transistor 24 is connected to a control power supply, and the collector is connected to an FET via a resistor 25.
Connected to the drain of II.

The operation will be explained below.

When the power is turned on, the collector voltage V of the switching element 5 is full-wave rectified by the full-wave rectifier 1.

At this time, the terminal voltage o of the capacitor 20 is the collector voltage v
Higher than T. Since diode 15 is not conducting, capacitor 20 is charged through resistor 17. Accordingly, the terminal voltage V of the capacitor 20 increases. rises and finally turns on transistor 21, which causes transistor 2 to turn on.
4 is also turned on. When the transistor 24 is turned on, an on-voltage is applied to the base of the switching element 5, and the switching element 5 is turned on. As a result, self-oscillation is started.

During the oscillation period, the specific number of discharges of the discharging circuit composed of the resistor 16 and the capacitor 20 is larger than the charging time constant of the charging circuit composed of the resistor 17 and the capacitor 20, so that the terminal voltage of the capacitor 20 is ■.

is very low. However, when the power supply voltage becomes around 0■, the base voltage of the switching element 5 becomes
There is no longer enough voltage to turn on the oscillation, and oscillation stops. At this time, the output voltage of the full-wave rectifier 1, that is, the power supply voltage is applied to the collector voltage (A) of the switching element 5.

When this power supply voltage increases from Ov and the collector voltage V becomes larger than the terminal voltage of the capacitor 20, the diode 15 is turned off, the discharging of the capacitor 20 is completed, and charging is started, and the terminal voltage becomes ■. rises. This terminal voltage vc
When a certain voltage is reached, transistor 21 and transistor 24 are turned on one after another, and a drive signal is sent to the base of switching element 5. This operation is repeated to continue continuous oscillation.

(G) Effects of the Invention According to the present invention, oscillation can be continued even when the power supply voltage is low at the start of oscillation, and abnormal noise can be prevented from occurring at the start of oscillation.

[Brief explanation of drawings]

FIG. 1 is a conventional operating circuit diagram, FIG. 2 is an operating waveform diagram of the main part of FIG. 1, and FIG. 3 is an operating circuit diagram of the present invention. 5... Switching element, 6... Transformer, 7...
・Magnetron, 11...FET, 14...control circuit.

Claims (1)

[Claims] (1) An inverter circuit consisting of a resonant capacitor, a switching element, a diode connected antiparallel to the switching element, and a primary winding of a transformer, and an inverter circuit connected to a secondary winding of the transformer. A magnetron, and a base winding that is electromagnetically coupled to a primary winding of the transformer, the base winding being connected to the switching element to supply an ON signal to the switching element, the terminal of the switching element A voltage detection section that detects a voltage, a signal output section that outputs a signal when the voltage detection section detects that oscillation has stopped, and a power supply section that supplies on power to the switching element; A magnetron drive device, wherein on-power is supplied from the power supply section to the switching element in response to a signal.