JPS61199468A - Switching power source system - Google Patents

Abstract

PURPOSE:To prevent the sharing voltage of a capacitor from unbalancing by connecting a plurality of capacitors connected in series with a DC high voltage, and connecting another switching power source with every capacitor. CONSTITUTION:An AC power source 10 is converted by a rectifier 11 to a DC, a ripple is removed by a capacitor 21 and 22 connected in series, converted by an inverter 15 to AC power of variable voltage and variable frequency to variably drive a motor 16. Since the capacitors 21, 22 are divided at the DC voltage, switching regulators 30, 40 as switching power source are connected in parallel, their transistors 31, 41 are turned ON and OFF, and a desired DC power is produced through transformers 32, 42 and output diodes 33, 43. Since the both transistors 31, 41 are turned ON and OFF by the time difference of T/2, the sharing voltages of both are not unbalanced.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to a switching power supply system for controlling a switching power supply connected in parallel to each of a plurality of capacitors connected in series.

[Prior art and its problems]

A switching power supply that inputs DC power and converts it into DC power of a desired voltage, such as a switching regulator, has a large capacitor connected to its input side. Therefore, it is common to use an aluminum electrolytic capacitor, but when the input DC voltage is high, due to restrictions on the rated voltage of the aluminum electrolytic capacitor, a plurality of capacitors are often connected in series. FIG. 6 is a circuit diagram showing a conventional example of a switching power supply device, and shows a case where two DC input capacitors are connected in series. That is, in this Fig. 6, AC power supply 1o
The AC power from is converted into DC power by the rectifier 11 and then applied to the switching power supply 25 via the two series-connected capacitors 21 and 22, so that the DC power of the desired voltage is supplied from the output terminal 1. Output. However, if the voltage of the AC power supply 10 in FIG. 6 is 440 volts AC, the peak value of the DC voltage output from the rectifier 11 is twice this, ie, 622 volts. This DC voltage peak value is applied as a power supply voltage to a semiconductor switch element (not shown) used in the switching power supply 25, and a reset voltage of the load transformer that is approximately equal to this power supply voltage is superimposed. In addition, the jump voltage when the semiconductor switch element turns off is also applied, so if power supply voltage fluctuations are taken into consideration, when the voltage of the AC power supply 10 is 440 volts,
The semiconductor switch element in the switching power supply 25 needs to have a voltage rating of about 1400 volts, but devices with such a high voltage rating have the disadvantage of being expensive. FIG. 7 is a circuit diagram showing a conventional example of a capacitor voltage division type switching power supply device, in which the DC voltage obtained by the AC type a10 and the rectifier 11 is divided by capacitors 21 and 22, and the capacitor 21 is connected to the switching power supply. 26 are connected in parallel, and a switching power supply 27 is connected in parallel to the capacitor 22, thereby reducing the voltage applied to each switching power supply to a value divided by the capacitor, thereby covering the above-mentioned drawbacks. That's what I do. Note that the output sides of both switching power supplies 26 and 27 are connected in parallel and taken out from an output terminal 18. FIG. 8 is a circuit diagram showing a different conventional example of a capacitor voltage division type switching power supply device. 8, a resistor 28 is connected in parallel to one capacitor 21, and a switching power supply 27 is connected in parallel only to the other capacitor 22.
The DC power converted is taken out from the output terminal 18. In the conventional circuits shown in FIGS. 7 and 8 described above, the voltage applied to the semiconductor switch elements built into the switching power supply is halved, so the cost of these semiconductor switch elements can be reduced. However, in the conventional circuit shown in FIG. 7, an unbalance occurs between the input currents of the switching power supplies 26 and 27, and in another conventional circuit shown in FIG.
There are drawbacks to inputting.

[Purpose of the invention]

The present invention provides a switching power supply system in which a DC high voltage is divided by a plurality of capacitors connected in series, and when a switching power supply is connected in parallel to each of the capacitors, no imbalance occurs in the shared voltage of each capacitor. The purpose is to

[Key points of the invention]

This invention divides a DC high voltage using multiple capacitors connected in series, connects a switching power supply to each capacitor to reduce the magnitude of the input DC voltage, and connects the output side of each switching power supply in parallel. By determining the conduction time of the built-in semiconductor switching elements so that each switching power supply shares the load equally, the shared voltage of each capacitor is balanced so that the equivalent resistance seen from the capacitor side is the same for each capacitor. It is an attempt to do so.

[Embodiments of the invention]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In FIG. 1, AC power from an AC power source 10 is converted to DC power by a rectifier 11, ripples are removed by capacitors 21 and 22 connected in series, and then an inverter 15 is used to convert the AC power into DC power with variable voltage and variable frequency. It is converted into electric power and drives the electric motor 16 at variable speed. Capacitors 21 and 22, which have the function of smoothing the DC power output from the rectifier 11, divide this DC voltage on the one hand, so a switching regulator 30 as a switching power supply is connected in parallel to the capacitor 21, and the capacitor 22 When the switching regulator 40, which also serves as a switching power supply, is connected in parallel, the voltage applied to each switch regulator is generally equal to the capacitor 21.
Since and 22 have the same capacity, the value is half of the DC voltage output by the rectifier 11. In the switching regulator 30, a transistor 31 as a semiconductor switch and a primary winding of a transformer 32 are connected in series.
0, the transistor 41 as a semiconductor switching element and the primary winding of the transformer 42 are connected in series, so
By turning on and off the transistors 31 and 41, the output diode 3 is connected to the secondary winding of the transformer 32.
The desired DC power can be extracted through 3.
Similarly, since DC power can be taken out via the secondary winding of the transformer 42 and the output diode 43, desired DC power can be obtained at once from the output terminal 18 by connecting these two in parallel. Note that numerals 34 and 44 are diodes, and numerals 35 and 45 are constant voltage diodes. With such a configuration, even if the voltage of the AC power supply 10 is 440 volts, for example, the voltage of the transformer that is superimposed on the power supply voltage, the voltage jump when the transistor turns off, and fluctuations in the power supply voltage can be taken into account. Also, since the rated voltage of the transistors 31 and 41 is only about 700 volts, low-cost transistors can be used as the semiconductor switching elements. These two transistors 31 and 41 are collectively controlled on/off by a control circuit 70. That is, the oscillator 71
is applied to the base of the transistor 31 via the photocoupler 72, and an on/off signal with a period of T is applied from the oscillator 71 to the base of the transistor 31 via the photocoupler 73.
It is designed to be given on the basis of 2 is an operation time chart of each transistor in the embodiment circuit shown in FIG. 1, in which FIG. 2(a) shows the operation of transistor 31, and FIG.
It is raining the action of 1. That is, both transistors 3
The on/off periods of both switching regulators 30 and 41 are T, but since they perform on/off operations with different time differences, the average one cycle of the input currents of the switching regulators 30 and 40 are approximately equal, and as seen from the capacitor 21. Since the equivalent resistance seen from the capacitor 22 and the equivalent resistance seen from the capacitor 22 have approximately the same value, the voltages shared between the capacitors 21 and 22 will not become unbalanced. FIG. 3 is a circuit diagram showing a second embodiment of the present invention,
If the power supply voltage is higher, it is likely to occur. In this Figure 3, the DC high voltage from the DC power supply 12 is divided by three capacitors 21, 22, and 23 of equal capacity, so three sets of switching power supplies are connected in parallel to each capacitor. The switching regulators 30, 40, 50 each share a voltage of A. In FIG. 3, numerals 31, 41, and 51 are transistors as semiconductor switch elements, and numerals 32, 42, and
．． 52 is a transformer, 33°43.53 is an output diode, 34, 44.54 is a diode, 35.4
Reference numeral 5.55 represents a constant voltage diode, and reference numeral 18 represents an output terminal, but since their functions and operations are the same as in the case of FIG. 1, their explanation will be omitted. FIG. 4 is an operation time chart of each transistor in the second embodiment circuit shown in FIG.
4(B) shows the operation of the transistor 41, and FIG. 4(C) shows the operation of the transistor 31, and FIG.
．． ．． The capacitors 21. , 22.23 are balanced. FIG. 5 is a circuit diagram showing a third embodiment of the present invention, and shows a case where a center-tapped transformer is used as a transformer built into a switching power supply. In FIG. 5, the output voltage of the DC power supply 12 is divided into two by two equal capacitance capacitors 21 and 22. A switching regulator 60 as a switching power supply includes a center-tapped transformer 63 and transistors 61 and 62 as semiconductor switching elements at both ends of the primary winding of the transformer 63.
The center tap of the primary winding of this transformer 63 is coupled to the midpoint between capacitors 21 and 22. Further, the secondary winding of the transformer 63 has an output rectifier 1i64 composed of bridge-connected diodes, and the DC output from the rectifier 64 is taken out from the output terminal 18. In FIG. 5, by turning on and off two transistors 61 and 62, which operate at a cycle T, with different time differences, capacitors 21 and 22 can achieve the desired voltage while sharing the current and voltage A. DC power can be obtained.

【Effect of the invention】

According to this invention, a plurality of, for example, N capacitors connected in series are connected to a DC high voltage, and
By connecting a separate switching power supply to each capacitor, the voltage applied to the semiconductor switch element built into the switching power supply is divided by the capacitor and can be made to a low value. can be used at low cost. Furthermore, by turning on and off these semiconductor switching elements, which operate on and off at a period of T, with a time difference of %, it is possible to equalize the value of the equivalent resistance seen from each capacitor. It is possible to exhibit the effect of preventing the shared voltages from becoming unbalanced.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is an operation time chart of each transistor in the embodiment circuit shown in Fig. 1, and Fig. 3 shows a second embodiment of the invention. 4 is an operation time chart of each transistor in the second embodiment circuit shown in FIG. 3, and FIG. 5 is a circuit diagram showing a third embodiment of the present invention. Fig. 6 is a circuit diagram showing a conventional example of a switching power supply device, Fig. 7 is a circuit diagram showing a conventional example of a capacitor voltage division type switching power supply device, and Fig. 8 is a circuit diagram showing a conventional example of a capacitor square type switching power supply device. FIG.

Claims (1)

[Claims] 1) N capacitors are connected in series to a DC power source, and a series circuit of a separate semiconductor switch element and a transformer primary winding is connected in parallel to each of the capacitors. In addition, in a switching power supply circuit in which the DC sides of the secondary windings of the transformer are connected in parallel to each other via a rectifier, the on-off period of each semiconductor switching element is divided by N. A switching power supply system characterized by sequentially turning on and off each semiconductor switch element using a time difference based on the value of the current value. 2) In the switching power supply system according to claim 1, when the primary winding of the transformer is a center-tapped winding, each semiconductor switching element is turned on and off with a time difference of N=2. Features a switching power supply system.