JPS61279094A - Power source unit for 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 Field of the Invention The present invention relates to a power supply device for a magnetron.

BACKGROUND OF THE INVENTION A conventional example will be described below with reference to FIG. A commercial type @1 is connected in parallel with the primary winding 3 of the isolation transformer 2, and the cathode side of the high voltage diode 7 is connected in parallel with the secondary high voltage winding 4. A high voltage capacitor 6 is connected in series with the secondary high voltage winding 4 to the opening on the anode side,
A magnetron 8 is connected in parallel with the high voltage diode 7, and the tertiary low voltage winding of the isolation transformer 2, I? In a magnetron power supply device in which a magnetron heater is connected in parallel with I5, a secondary high voltage winding 4 generates a high voltage, and a high voltage capacitor 6 and a high voltage diode 7 generate a double voltage. It's working.

Further, a high frequency filter 9 consisting of an inductance and a capacitor connected to the heater of the magnetron 8 prevents the high frequency waves generated by the magnetron 8 from flowing into the commercial power supply 1 through the isolation transformer 2.

Problems to be Solved by the Invention Recently, in order to reduce the size and weight of electronic devices, switching power supplies are being used. There is also a desire for power supplies for magnetrons to be smaller and lighter, and making them smaller and lighter can be achieved by increasing the frequency using a switching method.

Furthermore, conventionally, when changing the high frequency output of the magnetron, this was achieved by making the high voltage capacitor 6 shown in Figure 3 variable or by controlling the duty of the voltage applied to the isolation transformer 2. could not be continuously controlled.

In the high frequency inverter method, the high frequency output of the magnetron can be controlled by controlling the high frequency output voltage using pulse width control.

FIG. 4(A) shows a push-pull type circuit as a general example of a high frequency inverter. The operation of this circuit is as follows: the first switching element Tr□11 and the second switching element T
By turning r212 ON and OFF at the timing shown in the timing chart of FIG. 4(B), the DC power supply E13
If we consider converting the power supply for the magnetron into an inverter using the circuit shown in Figure 2, which switches the flow of current from the current source and induces an AC output voltage ■015 at the switching frequency in the secondary winding of the isolation transformer 14, the AC output A conceivable configuration is to use the voltage VO for the high frequency output of the magnetron, and to wind a tertiary winding around the isolation transformer 14 and use it for the heater power source of the magnetron. However, when trying to control the high frequency output of the magnetron, the switching elements Tr□ and Tr were turned on.
・Changing the OFF frequency.

The power for the magnetron heater also changed at the same time.
The magnetron cannot oscillate stably. Therefore, a separate transformer that is not affected by the control is required for the magnetron heater power, which increases the cost. In addition, since the high voltage required for magnetron oscillation is secured by the turns ratio of the transformer, the transformer does not become smaller, and the switching element Tr.

The control circuit becomes complicated because the transistors are made conductive alternately.

Furthermore, as a problem caused by increasing the frequency, the magnetron heater has 245
A high-frequency filter is provided to prevent the oscillation frequency of 0 MI and its high frequency from flowing into the commercial power supply side, so if only the high-frequency voltage generated by switching is applied, the heater current will be reduced by the inductance of this high-frequency filter. Since the heater current necessary for magnetron oscillation does not flow, the magnetron does not oscillate.

The present invention solves this problem by making the isolation transformer smaller and lighter, and simplifying the control circuit.
Moreover, the purpose of the heater circuit is to provide a power supply device for a magnetron that is not affected by high frequency output control.

Means for Solving the Problems In order to solve the above conventional problems, the present invention changes the circuit system from a push-pull system using two switching elements to a forward converter system using one switching element, and converts the primary, An isolation transformer consisting of secondary and tertiary windings is provided, and a capacitor is connected in parallel with the primary winding to form a parallel resonant circuit.

connecting a switching element in series with the parallel resonant circuit;
A flywheel diode is connected in parallel with the switching element, a capacitor for storing energy is connected in parallel with the parallel resonant circuit and the switching element, and a half-wave multiplier is connected to the same polarity side as the primary winding of the secondary high voltage winding. The cathode side of the diode of the voltage rectifier circuit is connected, and the half-wave voltage doubler rectifier circuit is connected between the anode and cathode of the magnetron to form a high voltage circuit, and the polarity is the same as that of the primary winding of the tertiary low voltage winding. The anode side of a half-wave rectifier smoothing circuit is connected to the side, and the half-wave rectifier smoothing circuit is connected to a heater of a magnetron to form a heater circuit, and when the switching element is conductive, current flows through the magnetron and the heater circuit. This is how it was done.

Function: With this configuration, a parallel resonant circuit is applied to the high frequency switching power circuit, so the high resonant voltage generated can be boosted to an even higher voltage by the secondary high voltage winding, causing the magnetron to oscillate. Can be made small and lightweight. Furthermore, since there is only one switching element, the control circuit can be simplified. Furthermore, since it is converted into a DC voltage by a half-wave rectifying and smoothing circuit and applied to the magnetron heater, it is not affected by high frequency output control.

EXAMPLE An example of the present invention will be described below based on the drawings. 1st
In the figure, 21 indicates primary, secondary, tertiary windings 22, 23 .
24, whose primary winding 22 and the
A switching element 26 is connected in series to a parallel resonant circuit formed by connecting a first capacitor 25 in parallel with the inductance of the next winding 22.
A flywheel diode 27 is connected in parallel to the parallel resonant circuit and the switching element 26, and a second capacitor 28 is connected in parallel to the parallel resonant circuit and the switching element 26.

Direct current in parallel to this second capacitor 28! G29 is connected to configure a primary circuit that becomes a high frequency switching power circuit, and the cathode side of the first diode 30 is connected in parallel with the secondary high voltage winding 23 to the same polarity side as the primary winding IQ22, and the secondary high voltage A third capacitor 31 is connected to the anode side of the first diode 30 in series with the winding wire 23, and a magnetron 34 is connected in parallel with the first diode 30.
The anode of the second diode 32 is grounded to form a secondary circuit that becomes a high voltage circuit of half-wave voltage doubler rectification, and the anode side of the second diode 32 is connected in series with the tertiary low voltage winding 24 and on the same polarity side as the primary winding 22. A fourth capacitor 33 is connected to the cathode side of the second diode 32 in parallel with the tertiary low voltage winding 34, and a heater of the magnetron 34 is connected in parallel with the fourth capacitor 33 to form a half-wave rectification smoothing heater. Configure a tertiary circuit that becomes a circuit.

These primary, secondary, and tertiary circuits constitute a magnetron power supply device.

Next, its operation will be explained. When the voltage VflE is applied in the forward direction between the base and emitter of the switching element 26, the switching element 26 becomes conductive, and the voltage V of the DC power supply 29
A second capacitor 28 in which energy is stored by Dc
As a result, vDa is applied to the primary winding 22 of the isolation transformer 210, and a current IIJ1 flows in the direction shown in the figure. Next, when voltage VBE is applied in the opposite direction between the base and emitter of the switching element 26, the switching element 26 is cut off, and the inductance seen from the primary winding 22 side of the isolation transformer 21 and the first capacitor 251 resonate in parallel. A high resonant voltage -VN (in the opposite direction to that shown) is generated. This resonant voltage -VN is made even higher voltage by the secondary high voltage winding 23 and charges the third capacitor 3I. Further, the voltage vod across the primary winding 22 when the switching element 26 is conducting is also boosted by the secondary high voltage winding 23, and the third capacitor 31 and the first
The voltage is added to the voltage of the third capacitor 31 by a voltage doubler rectifier circuit including a diode 30, and is supplied between the anodes and cathodes of the magnetrons 1 to 34, and when the switching element 26 is conductive, the magnetron oscillates.

Further, the VOC applied to both ends of the primary winding 22 when the switching element 26 is turned on is reduced in voltage by the tertiary low voltage winding 24,
A second diode 32 and a fourth capacitor 33 perform half-wave rectification and smoothing to supply a DC low voltage to the heater circuit of the magnetron 34.

Furthermore, when the conduction time of the switching element 26 is changed, the current IN flowing through the primary winding 22 changes, and the supplied energy VDcX1. As the construction changes, the energy supplied to the magnetron 34 also changes. Now, assuming that the conduction time of the switching element 26 is ToN and the cutoff time is TOFF, changing the TON time while keeping the switching frequency f and TON+TOFF OFF constant is equivalent to changing f. As shown in Figure 2 (D), there is a fairly linear relationship between the TON time and high frequency output, and between the switching frequency f and high frequency output, so by changing the ToN time or f, the high frequency output can be continuously varied. can be controlled.

The peak value of the voltage appearing in the tertiary low voltage winding 24 is shown in Figure 2 (
As shown in A), the number of turns of the primary winding 22 and the tertiary low voltage winding 24 is set to n0. n, then (nt / nt)
- V oa, and when the TON time changes, the peak value is always constant, but the effective value V11 changes, and by appropriately selecting the value of the fourth capacitor 23 of the tertiary circuit of half-wave rectification and smoothing, it can be kept constant. The heater can be heated with constant energy without being affected by high frequency output control.

The relationship between the parallel resonant circuit of the primary circuit and the voltage and current generated in the switching element 26 when the switching element 26 is turned OFF, that is, VBE, INi, VNt,
The relationship between Ic and V(!E is shown in the timing chart of FIG. 2(B).

Now, the switching element 26 is ON for 'I' ONL,...
If this is repeated with the TOFF period OFF, the law of equal ampere turns holds between the primary and secondary windings 22 and 23 of the isolation transformer 21 during the ON period, so l5
t=
The amount proportional to is transmitted to the secondary side, but the excitation current component is stored as is in the isolation transformer 21 and becomes residual energy. Further, vDc is added to VN□, and VCE becomes almost zero (to be exact, VaEcgai) 42V).

Next, when the switching element 26 is turned off, the IN
A current ■N1 begins to flow in the opposite direction to the first capacitor 7.
5 and the inductance seen from the primary winding 22, a high parallel resonance voltage with the opposite polarity during the ON period is generated at VNL, a voltage of VDc - VN is generated at vcE, and Ic is zero. becomes.

Next, Figure 2 (C) shows the relationship between VDE, IN+, and VN when the TOFF time is constant and the TON time is varied. Now, turn on the switching element 26.
When turned ON for 1 hour, the peak value of INt(7) becomes I'Nt, VNl becomes VDC, and the voltage VN□ generated by parallel resonance during the TOFF period becomes v'N1. Also T
ON When turned ON for ToNz time longer than l, INx
The peak value of is 1'H□, vIll is VDC,
The voltage VN generated by parallel resonance during the TOFF period is v'N□.

That is, when T ONt < T ONz, ON
In the period I'nl<I'Nxt vN1=v
,,c, It can be seen that there is a relationship of V'Nl,<V'Nd during the OFF period.

Therefore, by controlling the ON time of the switching element 26,
It is possible to control IN during the ON period and VN during the OFF period. Since the relationship between the TON time, the high frequency output, and the high frequency output is linear as shown in Figure 2 (D), the high frequency output can be continuously variable by controlling the TON time or switching frequency. I can do it.

In addition, by utilizing the high parallel resonant voltage during the OFF period, the third
Since the voltage doubler rectification method is used to charge the capacitor 31 and supply it to the magnetron in addition to the voltage during the ON period,
The number of turns of the secondary high voltage winding 23 can be reduced, and at the same time
A current IN2 flows through the secondary high-voltage winding 23 during both the OFF period and the direction of the current during each period is opposite, so that the isolation transformer 21 is not biased, and as a result, the isolation transformer 21 can be made smaller and lighter.

In addition, the voltage supplied to the heater of the magnetron 34 is determined by lowering the constant voltage Vna during the ON period using the tertiary low voltage winding 24 and converting it into a DC voltage using a half-wave rectifying and smoothing circuit, as shown in FIG. 2(A). Since the device is used, there is little effect even if the TON time changes due to high frequency output control. For example, when controlling the high frequency output from 100W to 600W, the fluctuation in heater voltage is within 10%, which poses no practical problem.Also, since DC voltage is supplied to the heater, the inductance and capacitor attached to the heater circuit It is not affected by the high frequency filter 35 at all. Further, an anode current with a frequency corresponding to the switching frequency flows through the magnetron 34, but the impedance of the inductance of the high frequency filter 35 at the frequency is approximately 0.3Ω, which is approximately 1.0Ω of the equivalent impedance during magnetron oscillation. It is sufficiently small compared to OKΩ, and the anode current flows without any problem.

In addition, the surge voltage generated in the primary winding 22 of the isolation transformer 21 when the switching element 26 turns from ON to OFF is controlled by the loop of the first capacitor 25-second capacitor 28-flywheel diode 27, which is shown by the broken line in FIG. This absorbs the surge voltage and prevents the switching element 26 from being destroyed by surge voltage.

In addition, the forward converter system using one switching element simplifies the circuit configuration, simplifies the control circuit, and reduces costs.

Effect of the invention The present invention has the following effects.

(1) Since a parallel resonant circuit is applied, the number of turns of the secondary high voltage winding of the isolation transformer can be reduced, allowing the isolation transformer to be made smaller and lighter.

(2) Since it is a one-system inverter system, both the basic circuit and the control circuit are simple.

(3) Since DC voltage is applied to the heater circuit by a half-wave rectifying and smoothing circuit, it is not affected by high frequency output control.

[Brief explanation of drawings]

Fig. 1 is a basic circuit diagram of a magnetron power supply device according to an embodiment of the present invention, Fig. 2 (A) is a diagram showing the relationship between ON/OFF of switching elements and heater voltage, and Fig. 2 (B
) is a timing chart of the primary circuit when the switching element is 0N=01"F, Figure 2 (C) is a principle diagram of high frequency output control, and Figure 2 (D) is TON time and high frequency output, switching frequency and high frequency output 3 is a basic circuit diagram of a conventional magnetron power supply device, and FIG. 4 is a basic circuit diagram of a push-pull type as a general example of a high frequency inverter. 21... Isolation transformer, 22... Primary winding, 23...
...Secondary high voltage winding, 24...Third low voltage winding, 25...
・First. Capacitor, 26... Switching element, 2
7... Flywheel diode, 28... Second capacitor, 29... DC power supply, 30... First diode, 31... Third capacitor, 32... Second diode, 33... Third 4 Capacitor, 34...Magnetron, 35...High frequency filter agent Yoshihiro MorimotoFigure 1 Figure 2 (D) 0″cON time - Figure 3, 5 Figure 4

Claims (1)

[Claims] 1. High-frequency switching is performed by a transformer consisting of a primary winding, a secondary high-voltage winding, and a tertiary low-voltage winding, a capacitor for resonating with the inductance of the primary winding, and a switching element having a flywheel diode. A power circuit is formed, and the cathode side of a diode of a half-wave voltage doubler rectifier circuit is connected to the same polarity side as the primary winding of the secondary high voltage winding, and the half-wave voltage doubler rectifier circuit is connected to the anode of the magnetron.・Connect between the cathodes to form a high voltage circuit, connect the anode side of a diode of a half-wave rectification and smoothing circuit to the same polarity side as the primary winding of the tertiary low-voltage winding, and connect the anode side of the diode of the half-wave rectification and smoothing circuit. 1. A power supply device for a magnetron, wherein a heater circuit is formed by connecting a circuit to a heater of a magnetron, and a current is caused to flow through the magnetron and the heater circuit when the switching element is conductive.