JPS62225164A - Switching power source - Google Patents

Abstract

PURPOSE:To supply a load with stable voltage, by a method wherein a first voltage source and a second voltage are connected in series, and output variation of the first voltage source is compensated by adjusting output of the second voltage source. CONSTITUTION:A primary winding of a transformer 20 and a controllable switch 30 are connected in series to a DC power source 10. A first voltage source 50 outputting voltage value proportional to voltage generated in a secondary winding of the transformer 20 during ON-period of the controllable switch 30 is connected to the secondary winding. A second voltage source 60 is connected in series to the first voltage source 50, and ontput voltage of the second voltage source 60 is adjusted, thereby variation of the output voltage of the first voltage source 50 is compensated and a load 70 is supplied with stable required voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching power source, and more particularly to a switching power source suitable for driving a nonlinear load such as a magnetron used as a microwave source in a microwave oven.

[Conventional technology]

Conventional magnetron power sources for microwave ovens, for example, are described in Electronic Technology Vol. 20, No. 3 (1973) 9.34.
As described in 45, this is a circuit that boosts a commercial AC voltage using a transformer, rectifies it using a half-wave voltage doubler rectifier circuit on the secondary side of the transformer, and applies a DC voltage to the magnetron. Control was performed by controlling the energization phase of a bidirectional controllable switch directly connected to the primary side of the transformer.

[Problem that the invention seeks to solve]

However, in the above conventional technology, the transformer of the microwave oven's i-gnetron power supply is operated at commercial frequency, so this transformer is large and heavy, and the commercial frequency is ei50H.
z, 60Hz, it was necessary to design separately. Furthermore, when the applied voltage between the anode and cathode of the load magneto A7 exceeds the cutoff voltage, the anode current starts to flow, and as the applied voltage increases, the anode current increases linearly and the microwave output is changed. It has a characteristic that when a critical value is reached, abnormal oscillation occurs and no microwave output can be obtained, and this abnormal oscillation significantly shortens the life of the magnetron. Moreover, the cutoff pressure of the magnetron is, for example, about 4 kV, and this value changes depending on the temperature of the magnetron, and fluctuates by several hundred volts during normal operation. However, in the conventional technology, no consideration is given to the case where the power supply voltage and the cutoff voltage of the magnetron fluctuate. Furthermore, when the power supply voltage drops or the cutoff voltage rises, the voltage applied to the magnetron does not rise above the cutoff voltage, causing the problem that the microwave output is hardly visible. Furthermore, in order to solve this problem with conventional technology, the turns ratio of the transformer is set to such a value that the voltage applied to the magnetron is equal to or higher than the cutoff voltage even when the power supply voltage reaches its lowest value, and when the power supply voltage rises, the anode current is reduced. One possible method is to prevent abnormal oscillation by detecting the anode current and turning off the bidirectional controllable switch before it reaches a critical value, but in this case, a means for detecting the anode current is required, and the above There are also problems such as the control circuit of the bidirectional controllable switch becoming complicated.

The purpose of the present invention is to reduce the size and weight of the transformer so that it can be used as a power source for microwave ovens, etc., and furthermore, even when the power supply voltage and magnetron cut-off voltage fluctuate, it is not necessary to detect the anode current, and the necessary microwave power can be generated with a simple control circuit. Optimal for use in magnetron power supplies for microwave ovens that provide stable output, have good control characteristics against power supply voltage fluctuations, and can supply stable voltage power to nonlinear loads such as magnetrons with a simple circuit. The purpose is to provide a versatile switching power supply. [Means for solving the problem] The present invention turns on and off the primary winding of a transformer connected in series with a DC power supply and the controllable switch of the controllable switch circuit at high frequency, and uses the transformer at high frequency. By doing so, we aim to make the transformer smaller and lighter, but we will focus on the first-order point.

As a method of supplying the necessary power to the magnetron even when the t-source voltage and the cut-off voltage of the magnetron fluctuate in the magnetron power supply of a microwave oven, etc., there is a method of supplying power to the symmagnetron using a current source. For example, on
In the off-chopper method, the energy of the DC power source is stored as the excitation energy of the transformer during the ON period of the controllable switch of the primary winding of the transformer connected in series with the DC power source and the controllable switch circuit, and the energy of the DC power source is stored as excitation energy of the transformer during the OFF period of the controllable switch. In order to supply excitation energy to the magnetron as a transformer 6IT current source, even when the power supply voltage fluctuates, the on/off duty of the controllable switch is changed to control the excitation current of the transformer. Power can be supplied to the magnetron. However, the output power of the on-on chopper method is proportional to the square of the product of the power supply voltage and the on-off duty of the controllable switch, so when outputting constant power when the power supply voltage fluctuates, the on-off duty and the power supply voltage are inversely proportional. Therefore, it is necessary to provide the control circuit of the controllable switch with nonlinear characteristics, resulting in a multiple control circuit configuration. On the other hand,
In the on-chopper method, the output voltage is proportional to the on/off duty of the controllable switch, but since the output voltage is applied to the magnetron in proportion to the source voltage, abnormal oscillations may occur if the power source voltage fluctuates. A phenomenon occurs in which microwave output cannot be obtained unless the applied voltage exceeds the cutoff voltage.

The object of the present invention is to focus on the above, and to provide a series circuit of the primary winding of a transformer connected to a direct R'FII source and a turn section 1 switch, to turn on the controllable switch to the secondary winding of the transformer. A voltage source of 'gIJ1 which outputs a voltage proportional to the power supply voltage generated in the secondary winding during the period is connected, while a voltage source of the transformer is connected to the secondary winding of the transformer during the ON period of the controllable switch. After storing the excitation energy from the power supply in the excitation inductance, during the off period of the controllable switch, the excitation inductance of the transformer is used as a current source and a second voltage source is connected to which the stored energy is supplied. By configuring a load to be connected to the series circuit of the voltage source and the second voltage source, this can be achieved by combining the characteristics of the on-off chopper method and the on-on chopper method.

[Effect]

In the present invention, a tenth voltage source that outputs a voltage proportional to the voltage of the power source and a second voltage source that stores the energy of the power source in a current source and is supplied with energy from the current source are connected in series. Since the sum of the output voltages is applied to the load, when the power supply voltage fluctuates, the on/off duty of the controllable switch is changed to save the energy stored in the current source to the first voltage source and the second voltage source. By controlling, the fluctuation f in the output voltage of the first voltage source is compensated for by adjusting the output voltage of the second voltage source, and a stable desired voltage of magnetic force is supplied to the load.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 9.

Figure I@1 is a block diagram showing a first embodiment of a switching power supply according to the present invention. In FIG. 1, 10 is a DC power supply, 20 is a transformer, 30 is a controllable switch, 40
? 'i Controllable switch 300 control circuit, DC power supply 10
A series circuit of the primary winding of the transformer 20 and the controllable switch 30 is connected to.

50 is a first voltage source, 60 is a second voltage source, 70 is a load, and the first voltage source 5 is connected to the secondary winding of the transformer 20.
0 and the second voltage source 60 are connected, and a load 70 is connected to the series circuit of the first voltage source 50 and the second voltage source 60. Note that the same reference numerals indicate the same or corresponding parts throughout the drawings.

FIG. 2 is an example diagram of operation waveforms of each part in FIG. 1. The operation of the circuit shown in FIG. 1 will be explained with reference to FIG. As shown by the waveform shown by the solid line in FIG. 2, the first voltage source 50 connected to the secondary winding of the transformer 20 is proportional to the voltage of the DC power source 10 and the turns ratio of the transformer 200 during the ON period of the controllable switch 30. The voltage generated in the secondary winding of the transformer is output as the output voltage. A second voltage source 6 connected to the secondary winding of one transformer 20
0 is generated by using the excitation energy from the excitation I/L flow stored in the excitation inductance of the transformer 20 by the DC power supply 10 during the on period of the controllable switch 300 as a current source, and storing the excitation energy during the off period of the controllable switch 30. outputs the voltage as the output voltage. The shaded part of the excitation current waveform of the transformer 2o shown in FIG.
0Vc# represents the amount of charge that is multiplied. The load 7o connected to the series circuit of the first current source 50 and the second current source 60 is supplied with electric power having a voltage that is the sum of the direct voltage output of the first current source 50 and the output voltage of the second voltage source 60. supply. In this case, by changing the on/off duty of the controllable switch 30 by the control circuit 40, ? The power of the output voltage supplied to the L load 70 is made variable.

If the voltage of the DC 1 source 10 rises as shown by the waveform shown by the broken line in Fig. 2 when the power supply IT voltage fluctuates (broken line l), the control circuit 40 reduces the on/off duty of the controllable switch 3°. Then, the excitation energy caused by the excitation 111 flow of the transformer 20 is reduced, and the output voltage of the second voltage source 60 using this excitation energy as a current source is lowered, and the output voltage is proportional to the power supply voltage of the first 41E source 5o. By compensating for the increase in , stable heavy power is supplied to the load 70. Also, if the voltage of the DC power supply 10 drops (
(broken line ■), the on/off duty of the controllable switch 300 is increased to increase the excitation energy by the excitation current of the transformer 20, thereby increasing the output voltage of the second voltage source 60, and increasing the output of the first heavy pressure source 50. By compensating for the decrease in voltage.

Power with a stable output voltage is supplied to the load 70.

FIG. 3 is a circuit diagram of a magnetron power supply showing a second embodiment of the switching power supply according to the present invention.

In FIG. 3, 21 is the primary winding of the transformer 20, 22
is also a secondary winding, and the polarities of the primary winding 21 and secondary winding 22 are indicated by dots. 3.1 is a controllable switch 30i, a transistor %32 is a drive circuit for the transistor 31, and the collector of the transistor 31 is connected to the transistor 1 of the transformer 20.
It is connected to the positive side of the DC power supply 10 via the next winding 21, and the emitter of the transistor 31 is connected to the negative side of the DC power supply 10. 51 is a first diode forming the first voltage source 50;
2 is also the first capacitor, 61 is the second voltage source 60
62 is a second capacitor, 71 is a magnetron which is a load 70t, and 72n is a heater power source for the magnetron 71. transformer 20
The anode of the diode 51 and the cathode of the diode 61 are connected to one end of the secondary winding 22 of the transformer 20.
One end of the capacitor 52 and one end of the capacitor 62 are connected to the other end. The cathode of the diode 51 and the anode (ground) of the magnetron 71 are connected to the other end of the capacitor 52, and the anode of the diode 61 and the cathode of the magnetron 71 are connected to the other end of the capacitor 62.

FIGS. 4(a) and 4(b) are equivalent circuit diagrams in which the transistor 31 of FIG. 3 is in the on and off states, respectively. In FIGS. 4(a) and 4(b), 25 is the excitation inductance of the transformer 20. The circuit operation when the transistor 31 shown in FIG. 3 is turned on and off will be explained with reference to FIGS. 4(a) and 4(b). When the transistor 31 in FIG. 4(a) is turned on, the first diode 51 constituting the first voltage source 50 is conductive, and the first capacitor 52 is charged by the DC power supply 10 with a current in the direction of the arrow υ, and the load The magnetron 71 which forms part 70 has a charging voltage of capacitor 52 and fX which forms a second voltage source.
A voltage equal to the sum of the pressures of the two capacitors 62 is applied to supply power. Further, when the transformer is turned on, excitation energy generated by the excitation current in the direction of the arrow is stored in the excitation inductance 25 of the transformer 20 by the DC power supply 10. Figure 4(b) on one side
When the transistor 31 is off, a back electromotive force is generated in the secondary winding 22 of the transformer 20, the second diode 61 forming the second voltage source 60 becomes conductive, and the second capacitor 62 is The excitation energy stored in the excitation inductance 25 when turned on is 1! It is charged with the current in the direction of the arrow as a current source, and the magnetron 71 has a capacitor 5 of 741.
A voltage equal to the sum of the charging voltages of the second capacitor 62 is applied to supply power. In this case, the transistor 31 is driven by the control circuit 40 via the drive circuit 32 with an on/off duty determined from the voltage of the DC power supply 10 and the reference output power supplied to the magnetron 71.

Furthermore, when the voltage of the DC power source 10 fluctuates, the on/off duty of the transistor 31 is controlled in the same manner as in the embodiments shown in FIGS. By changing the charging voltage of the capacitor 62, fluctuations in the voltage applied to the magnetron 71 are suppressed to supply a predetermined output power.

FIG. 5 is an example diagram of operation waveforms of each part in FIG. 3. The circuit operation of the magnetron 71 shown in FIG. 3, including when the cutoff voltage varies, will be explained with reference to FIG. As shown by the waveform shown by the solid line in FIG. 5, the DC power supply 10 performs various operations during the on/off period of the transistor 31. When the cut-off voltage of the magnetron 71 fluctuates, as shown in the waveform shown by the broken line in FIG. Charging of the capacitor 62 during the OFF period of the transistor 31 in the first operation cycle 4r! The L pressure increases as shown. Also, if the cutoff pressure decreases, Ifi (dashed line ■)
, the anode' current, that is, the amount of discharge '4 of the capacitor 62 increases, so that the transistor 31 in the first operation cycle increases.
The charging voltage of the capacitor 62 during the off-period decreases as shown in the figure. In this way, the charging voltage of the capacitor 62 changes according to the fluctuation of the cutoff voltage of the magnetron 71,
Since the voltage applied to the magnetron 71, which is the sum of the voltage of the capacitor 52 and the charging voltage of the capacitor 62, changes, fluctuations in the anode current can be suppressed without control.

In this case, the relationship among the output power P, the DC power supply voltage E, the cutoff voltage Ec of the magnetron, and the on/off duty ρ of the h transistor is the switching frequency f of the transistor, the turns ratio n of the lance, and the excitation inductance L of the transformer. In contrast, the following equation is obtained.

6(a) and 6(b) are the characteristic sections of FIG. 3 obtained from the above formula, respectively, and the solid line in FIG. 6(a) is the DC power supply 10
FIG. 46(b) is a constant output power control characteristic diagram of the on/off duty of the transistor 31 with respect to fluctuations in the voltage of the magnetron 71. FIG. The broken line in FIG. 6(a) shows the characteristics of the conventional on-off chopper system. IX 619 (
The constant output power control characteristics of the on-off duty when the voltage of the conventional on-off chopper type DC power supply shown by the broken line in a) fluctuates is non-linear, whereas the voltage of the DC power supply 10 in Fig. 3 shown by the solid line The control characteristic of the constant output power P of the on/off duty ρ of the transistor 310 when E varies is almost linear.The cutoff voltage Ec of the magnetron 71 in FIG. 3 shown in FIG. 6(b) is The characteristic of the output cardiac force P when it fluctuates is almost flat, and the influence of the fluctuation of the cutoff voltage is small.

Thus, in the embodiment of FIG. 3, the secondary winding 22 and the first diode 51 are connected in series with a polarity that is conductive during the ON period of the transistor 31 and forms a current path to the first capacitor 52. A circuit is connected in parallel to the first capacitor 52 to form the first voltage source 50, while the circuit is connected in parallel to the first capacitor 52 to form the second capacitor 62.
The series circuit of the secondary winding 22 and the second diode 61 connected to the polarity forming a current path to the above! By connecting the second capacitor 62 in parallel to form the second voltage source 60, and connecting the series circuit of the first capacitor 52 and the second capacitor 62 in parallel to the magnetron 71, a simple circuit can be realized. With this configuration, it is possible to supply power at a stable voltage even when the power supply voltage and magnetron cutoff voltage fluctuate, and obtain a predetermined microwave output.

FIG. 7 is a circuit diagram of a magnetron power supply showing a third embodiment of the switching power supply according to the present invention.

In FIG. 7, 23 is the tertiary winding of the transformer 20.

The polarity is indicated by a dot. The embodiment of FIG. 7 is the embodiment of FIG.
A winding for extracting the excitation energy of the transformer 20 as a direct current source for a second voltage source 60 constituted by 2 is provided as a tertiary winding 23 separately from the secondary winding 22. The circuit operation and characteristics of this embodiment are similar to those shown in FIG.

FIG. 8 is a circuit diagram of a magnetron power supply showing a fourth embodiment of the switching power supply according to the present invention.

In FIG. 8, 11 is a commercial AC power supply, 12 is a rectifier circuit (rectifier bridge), and 13 is a power supply capacitor, which constitutes the DC power supply 1. In the embodiment shown in FIG. 8, the voltage of the DC power supply 1 shown in FIG. Control circuit 40 according to the instantaneous value
By controlling the on/off duty of the transistor 31 via the drive circuit 32t, a predetermined microwave output of the magnetron 71 can be achieved. Its circuit operation and characteristics are similar to those shown in FIG.

FIG. 9 is a circuit diagram of a microwave oven device showing a fifth embodiment of the switching power supply according to the present invention.

In Fig. 9, 1 is an AC outlet, 2 is a fuse, 3-piece power switch, 4 is a power switch, 5 is a door switch, and 6 is a control power transformer.

7 is a rectifier circuit, 8 is a constant voltage circuit, and 9 is a cooling fan. The circuit operation and characteristics of FIG. 9 are similar to those of FIG. 3 and the like.

〔Effect of the invention〕

As described above, according to the switching power supply of the present invention, 1!
Not only can the transformer be made smaller and lighter by using it at high frequencies by applying it to the magnetron power supply of a child microwave oven, etc., but it also has a duty control characteristic that is almost linear with respect to the tIL source voltage movement, and is suitable for magnetrons etc. Since the effect of nonlinear load characteristic fluctuations on the output power is small, a simple circuit configuration allows the magnetron to supply stable voltage power even when the power supply voltage and magnetron cutoff voltage fluctuate, resulting in stable microwaves. It has the effect of changing the output.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the first embodiment of the switching power supply according to the present invention, Figure 2 shows the operating waveforms of each part in Figure 1, and Figure 3 shows the second embodiment of the switching power supply according to the present invention. 4(a) is a circuit diagram showing the transistor shown in FIG. 3.(b) is an equivalent circuit diagram of the transistor shown in FIG.
Figures 6(a) and 6(b) show an example of the f-needle constant output power control characteristics when the power supply voltage fluctuates in Figure 3, and the cutoff [
How many sections are the focus control output power characteristics during pressure fluctuations? Fig. 7 is a circuit diagram showing a third embodiment of the switching power supply according to the present invention, Fig. 8 is a circuit diagram also showing a fourth embodiment, and Fig. 9 is a circuit diagram also showing a fifth embodiment. It is a diagram. 10...DC 1'' 20...Transformer, 21...
Primary winding, 22... Secondary winding 1" gland, 30... Controllable switch. : 31... Transistor, 40... Control circuit, 50
...first voltage source, 51...1 diode,
52...First capacitor, 60...Second 1 Shobara, 61...Second diode, 62...Second capacitor, 70...Load, 71...Magnetron.

Claims (1)

[Claims] 1. A series circuit of the primary winding of the transformer and the controllable switch is connected to a DC power supply, and the secondary winding of the transformer is connected to the secondary winding during the ON period of the controllable switch. A first voltage source that outputs the generated voltage and a second voltage source that stores excitation energy of the transformer using the excitation inductance of the transformer as a current source during an off period of the controllable switch, and A switching power supply comprising a series circuit of a voltage source and a second voltage source connected to a load. 2. The first voltage source comprises a first capacitor connected to the secondary winding and charged through a first diode conducting during the on-period of the controllable switch; 2. A switching power supply as claimed in claim 1, comprising a second capacitor connected to said secondary winding and charged through a second diode which is conductive during the off-period of said controllable switch. 3. The switching power supply according to claim 1 or 2, wherein the output power to the load is made variable by changing the on/off duty of the controllable switch. 4. The switching power supply according to claim 1 or 2, wherein fluctuations in output power to the load are suppressed by controlling the on/off duty of the controllable switch in accordance with voltage fluctuations of the DC power supply. 5. Claim 1 in which the load is a magnetron
The switching power supply according to item 1 or 2 or 3 or 4.