JPH02129894A - Power source for magnetron - Google Patents

Abstract

PURPOSE:To shorten starting time of a magnetron by controlling a switching device of an inverter circuit with frequency responding to an output of anode current detection of the magnetron. CONSTITUTION:At the time of immediate after power load, magnetron 12 does not oscillate and an output voltage of an anode current detection through a current transducer 13 becomes small as compared to a reference voltage of a reference circuit 18 and a first comparator 21 is turned on and an output of a comparison circuit 29 becomes the minimum value set by a lower limiter. By this, a pulse duration of output generated by a PWM circuit 33 becomes narrow and a driving circuit 34 is turned on within a short time by a trigger frequency of a high frequency responding to a detection anode current and cathode current is controlled. Then, when the cathode is warmed up and the magnetron is in a state to oscillate normally, the anode current becomes large, the comparator is turned off, and output of the circuit 29 is automatically set in the prescribed value by an upper limiter. Minimum output for a prescribed period is thus not needed and starting time of the magnetron is shortened.

Description

[Detailed description of the invention] (b) Industrial application fields The present invention relates to a power supply device for driving a magnetron.

(0) Conventional technology In recent years, in order to make electronic devices such as microwave ovens smaller and lighter,
Various types of power supplies for magnetrons have been proposed in which an inverter is used.

Generally, in an inverter power supply, the magnetron's cathode power is supplied from the tertiary winding of the high-voltage transformer, so the cathode is heated only after the inverter starts operating, until the cathode reaches a temperature sufficient for the magnetron to oscillate. requires a certain amount of time. and,
At the start of magnetron oscillation, the peak value of the collector current of the power transistor increases for several cycles compared to during steady operation due to a transient phenomenon, resulting in the problem of destroying the power transistor.

To solve this problem, Japanese Patent Application Laid-Open No. 62-66595 (HO5B6/68) proposes to maximize the switching frequency for several seconds after the inverter starts operating, thereby minimizing the microwave output and suppressing the collector current. We are proposing a method.

However, the time from the start of inverter operation to the steady oscillation of the magnetron varies by about 0.5 to 4 seconds, and as mentioned above, if the output is operated at the minimum output for a certain period of time and then shifted to the set output, the startup time The problem was that it took an unnecessarily long time.

(c) Problems to be Solved by the Invention The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a power supply device that can reduce the startup time of a magnetron.

(d) Means for Solving the Problems A detection means for detecting the anode current of the magnetron and a control means for controlling the switching elements of the inverter circuit at a trigger frequency according to the output of the detection means are provided.

(e) Operation Immediately after the power is turned on, the cathode temperature is low and the magnetron is not oscillating, so the anode current detected by the detection means is extremely small. The control means controls the switching elements of the inverter circuit at a high frequency, that is, with a short ON time, in accordance with the output of the detection means.

When the temperature of the cathode rises and the magnetron starts to oscillate normally, the anode current detected by the detection means increases, and the control means controls the inverter circuit so that the magnetron oscillates at the set output according to the output of the detection means. control the switching elements of.

(f) Example An embodiment of the present invention will be described in detail below based on the drawings.

(1) is a commercial power supply, (2) is a rectifier circuit, (3) is a choke coil, and (4) is a smoothing capacitor. (5) is a step-up transformer, whose primary winding (5a) is a power transistor (6) which is a switching element, and a freewheeling diode (
7) and resonant capacitor (8) together with the inverter circuit (
9). The switching of the power transistor (6) is controlled by a control means (35), which will be described later, so that high-frequency power having a frequency equal to the trigger frequency of the power transistor (6) is generated in the inverter circuit (9).

A magnetron (12) is connected to the secondary winding (5b) of the step-up transformer (5) via a capacitor (10) and a diode (1), and the high-frequency power generated by the inverter circuit (9) causes the secondary winding to be High frequency and high voltage power is generated in the winding (5b), and the capacitor (10) and diode (1
)) to supply a high DC voltage to the magnetron (12). The tertiary winding (5c) of the step-up transformer (5) is connected to the cathode of the magnetron (12) to supply cathode power.

(13) is a current transformer serving as a detection means for detecting the anode current of the magnetron (12), and is configured to output a voltage proportional to the anode current.

(14) is a smoothing circuit that averages the output voltage of the current transformer (13), which includes a diode (15), a resistor (1
6) and a capacitor (17). (18)
is a reference circuit that creates a reference value for a comparison circuit (29) to be described later, and is made up of a voltage dividing resistor (191 (20)).

(21) is a first comparator, which compares the output of the smoothing circuit (14) that is input to a child terminal with the reference value from the reference circuit (18) that is input to one terminal. , the output of the first comparator (21) is an upper limiter consisting of a diode (22) and a resistor (23+ (241), and a diode (25) and a resistor +261 (271
An upper limit value and a lower limit value are respectively set by a lower limit limiter consisting of: The first comparator (21) constitutes a comparison circuit (29) together with an upper limiter, a lower limiter, and a capacitor (28).

(30) is a variable resistor used by the user to adjust the output of the magnetron (12), and (31) is a second comparator, which connects the output of the variable resistor (30) input to the child terminal to one terminal. The input output of the smoothing circuit (14) is compared with the output of the comparison circuit (29), and the P
It is designed to output to the WM circuit (33). The variable resistor (30) and the second comparator (31) constitute a setting circuit (32).

(33) represents the output of the comparison circuit (29) and the setting circuit (3).
A PWM circuit (34) inputs the output of the PWM circuit (3) and outputs a pulse with a width proportional to the input.
3) is a drive circuit that controls the power transistor (6) of the inverter circuit (9) based on the output of the inverter circuit (9).

The smoothing circuit (14), the reference circuit (18), and the comparison circuit (
29), a setting circuit (32), a PWM circuit (33), and a drive circuit (34) constitute a control means (35).

Next, the operation will be explained.

When the output of the magnetron (12) is set using the setting circuit (32) by operating the variable resistor (30) and the power is turned on, the cathode is not warmed up immediately after the power is turned on, and the voltage to be magnified is set by the reference circuit (18). is smaller than the reference value, the first comparator (21) is turned on, and the output from the comparison circuit (29) becomes the minimum value set by the lower limiter. Since the output of this comparison circuit (29) is the minimum value, the PWM circuit (33)
) The width of the pulse generated by the drive circuit (34) becomes narrower.
controls the power transistor resistor (6) at a high frequency, that is, with a short ON time.

When the cathode warms up and the magnetron (12) starts normal oscillation, the anode current increases and the current transformer (12) starts to oscillate normally.
3) becomes larger than the reference value of the reference circuit (18), and the first comparator (21) becomes 0FFL and the comparison circuit (2
The output of 9) becomes the setting value of the upper limiter. Then, P
The width of the pulse generated by the WM circuit (33) is determined by the setting circuit (3).
The width corresponds to the magnetron output set in 2),
The drive circuit (34) controls the power transistor (6) of the inverter circuit (9) based on the output of the PWM circuit (33).
) to cause the magnetron (12) to oscillate at the set output.

When the output from the smoothing circuit (14) becomes larger than the output from the variable resistor (30), that is, when the output from the magnetron (12) becomes higher than the output set by the user, the second comparator (31) ONL
, the output to the PWM circuit (33) is lowered to maintain the output of the magnetron (12) at the output set by the user.

(G) Effects of the Invention As described above, according to the present invention, when the magnetron becomes in a state where it can normally oscillate, the magnetron can be automatically oscillated at the set output. This has effects such as being able to shorten the time.

[Brief explanation of drawings]

The drawing is a circuit diagram of one embodiment of the present invention. (6)...Power transistor (switching element)
, +91... Inverter circuit, (12)... Magnetron, (13)... Current transformer (detection means)
, +351...control means.

Claims (1)

[Claims] (1) In a device that drives a magnetron with high-frequency power from an inverter circuit, there is a detection means for detecting the anode current of the magnetron, and a control means for controlling the switching elements of the inverter circuit at a trigger frequency according to the output of the detection means. A power supply device for a magnetron, characterized by being provided with.