JPS601835B2 - power circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply circuit, and particularly to a power supply circuit for a magnetron.

The magnetron is a high-voltage drive element, and the power supply circuit that drives it is equipped with a large transformer for boosting the commercial frequency, so it has the disadvantage of being large in size and weight.

Therefore, in order to eliminate such drawbacks, transformers have recently been made smaller by converting DC power or commercial frequencies into high frequencies and supplying the same to the transformers.

FIG. 1 shows an example of this type of power supply circuit. In the figure, la and lb are thyristors connected in series to both ends of the commutating IJ vector 2, 3a and 3b are commutating capacitors connected in series, and the connection point between the capacitors 3a and 3b and the reactor A transformer 4 is connected between the midpoint of 2 and the midpoint of 2. The boosting output of this transformer 4 is connected to the diode 5a~
It is supplied to the magnetron 6 via the bridge circuit 5d. 7 is a power source, and the output obtained by rectifying a battery or a commercial frequency power source is used.

The operation of the power supply circuit having such a configuration is as follows.

That is, the control signal with the waveform shown in FIG. 2a is applied to thyristor la, and the control signal with the waveform shown in FIG. 2b is applied to thyristor l.
By supplying the signal to b, first, the thyristor la becomes conductive with the signal shown in a of the figure, and the reactor 2 and capacitor 3a are connected.
, 3b, the current shown in FIG. 2c flows with the vibration waveform determined by . When this current attempts to flow in the opposite direction due to vibration, the thyristor la is cut off. At this time, thyristor lb becomes conductive state by the control signal shown in Fig. 2b, and the oscillating current shown in Fig. 2d flows, and when this current similarly goes in the opposite direction, thyristor lb becomes in the discontinuous state. . Thereafter, by repeating the same operation, a high frequency oscillating power source as shown in FIG. 2e flows through the step-up transformer 4.
However, the power supply circuit having such a configuration has a drawback in that the current supplied to the magnetron 6 fluctuates considerably due to fluctuations in the power supply voltage and load fluctuations. In other words, the voltage-current characteristics of the magnetron are as shown in Figure 3.
Fluctuations in voltage-current characteristics due to temperature changes and load variations are shown in FIG.

As is clear from FIG. 3, the optimum setting voltage V. On the other hand, when there is a voltage fluctuation and changes from V0 to V-, the current lo changes significantly from 10 to 11. Also, as is clear from Figure 4, the characteristics change due to temperature changes and load variations.
Based on the fact that the current L changes around r+ and r-,
varies greatly from 10 to 11. In this way, when the current lo changes significantly, the magnetron not only causes a large output fluctuation, but also an excessive current flows, causing an abnormal state such as moding, and there is a risk that the magnetron itself may be destroyed. Therefore, an object of the present invention is to provide a power supply circuit that can always supply a constant current to a load such as a magnetron.

In order to achieve such an object, the present invention connects a saturable reactor whose inductance increases rapidly when the current exceeds a certain value in series with a step-up transformer, and will be explained in detail below using examples. do.

FIG. 5 is a circuit diagram showing a power supply circuit according to the present invention, particularly a power supply circuit for a magnetron, and the same parts as in FIG. 1 are denoted by the same reference numerals.

In the figure, ``8'' is a current limiting section which is a feature of the present invention, and is composed of a saturable reactor, the details of which are shown in Figure 6a. A main winding 1 which is a core having a core and which is wound in opposite directions to form a saturable reactor connected in series.
It has 0a and 10b. Reference numeral 11 denotes a control winding connected to the DC power supply 13 via a current limiting resistor 12, and the magnetic flux caused by this control winding 11 is superimposed on the magnetic flux of the main windings 10a and 10b in a certain direction. Become.

Therefore, the characteristics of the current limiting section 8 become as shown in FIG. As shown in Figure 7b, the inductance rapidly increases from the time when the current lc corresponding to the DC magnetic field Hc is reached. It changes like this.

Furthermore, the B-day characteristic at point B shifts in the opposite direction to that at point A, as shown in FIG. 7c. Therefore, from the time when the current -lc corresponding to the direct current magnetic field Dc per day is reached, the inductance rapidly increases. For this reason, the magnetron can be supplied with a constant current having an amplitude of 11 as shown in FIG.
In this case, since the gap g is formed in the core 9, there is no risk of high voltage being induced in the control winding 11. Note that FIGS. 8a and 8b show the timing of driving the thyristors la and lb shown in FIG. 5.

Here, the current limiting section 8 is not limited to the configuration shown in FIG. 6a, and may use a permanent magnet 14 instead of the control winding 11, as shown in FIG. 6b.

In this case, by providing the gap g, the reluctance of the magnetic circuit of the permanent magnet can be increased, and its extinction can be prevented. Further, the power source connected to the control winding 11 is not limited to a DC power source, but may be a rectified AC power source.

Further, the rectifier circuit is not limited to being constructed from a bridge circuit of the diodes 5a to 5d, but may be constructed from a voltage doubler rectifier circuit. As explained above, according to the power supply circuit according to the present invention, even if power supply fluctuations or load fluctuations occur, a constant amount of current can always be supplied to the magnetron, so fluctuations in the output of the magnetron can be prevented, and there is no risk of damage. It disappears.

In addition, when a rectified commercial frequency AC power source is used as the power source 7, the smoothing circuit can be simplified, the capacity of the smoothing capacitor can be reduced, and in some cases, it can be omitted, which greatly contributes to reducing the cost of the power source circuit. be effective.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an example of a conventional power supply circuit, Figure 2a
~e are waveform diagrams showing the operation of the conventional power supply circuit, Figures 3 and 4 are characteristic diagrams showing the voltage-current characteristics of the magnetron, and Figures 5 and 6 a and b are waveform diagrams showing the operation of the power supply circuit according to the present invention. 7a, b, c, d and FIG. 8 are waveform diagrams showing the operation of the power supply circuit according to the present invention. la, lh...Thyristor, 2...Reactor, 3a,
3b...Capacitor, 4...Transformer, 5a-5d...
Diode, 6... Magnetron, 7... Power supply, 8... Current limiting section, 9... Core, 1
0a, 10b... Main winding, 11... Control winding, 12... Resistor, 13... Power supply, 1
4...Permanent magnet. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. In a power supply circuit comprising an inverse conversion circuit having at least a thyristor, a commutating capacitor, and a commutating reactor, and a transformer connected to the output side of this inverting circuit, , and a current limiting section comprising a main winding whose inductance increases when a certain current value is exceeded is connected in series to the primary side of the transformer. 2. Claim 1, wherein a control winding to which DC bias is supplied is wound around the core constituting the current limiting section, and the magnetic flux saturation region of the main winding is controlled by this control winding. Power supply circuit as described. 3 Insert a permanent magnet into the iron core that constitutes the current limiting section,
2. The power supply circuit according to claim 1, wherein the permanent magnet controls the magnetic flux saturation region of the main winding. 4. The power supply circuit according to claim 1, wherein the output from the secondary winding of the transformer is supplied to the magnetron.