JP2008182870A - Power system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply system capable of improving the power factor as compared with the prior art and reducing the size of a transformer.
A power supply system 100 includes a power transformer 110 that converts AC 100V into AC 24V, and a plurality of power units 200-1 to 200-n connected to the power transformer 110. The power supply unit 200-1 includes a rectifier circuit 210 that rectifies AC 24V, a power factor improvement circuit 220 that improves the power factor of the rectified voltage, and an output circuit 230 that outputs a DC voltage. The power factor correction circuit 220 includes an inductor L, FET1, FET2, and a control circuit 222 that controls switching of the FET1 and FET2. The control circuit 222 adjusts the duty ratio of the FET1 and FET2 to obtain a desired direct current. The voltage is output from the output circuit 230.
[Selection] Figure 4

Description

  The present invention relates to a power supply system that supplies AC power from a single AC power supply to a plurality of power supply units, and more particularly to improvement of power factor in the power supply unit.

  As semiconductor devices and electronic devices are miniaturized and combined, driving voltages of internal power supplies used in those devices and devices are diversified. For example, in a semiconductor device such as a CPU or a memory, the circuit line width is reduced in order to achieve high density integration, and accordingly, the drive voltage is decreased from 5V to 3.3V and 1.8V. In addition, driving voltages for driving liquid crystal displays, audio devices, recording media, semiconductor devices, and the like may be different in electronic devices such as mobile phones, computers, OA equipment, in-vehicle electronic devices, and gaming machines. For example, drive voltages of 24V, 12V, 5V, 3.3V, and 1.8V are required.

  Against this background, the power supply device is required to supply various drive voltages. When a desired DC voltage is generated from a commercial AC voltage or a DC voltage, a switching power supply is widely used. The switching power supply generates a DC voltage obtained by converting the input DC voltage by adjusting the duty ratio of the on / off switching of the transistor.

  FIG. 1 is a circuit diagram showing an example of a conventional step-down switching power supply device. The transistor Tr is connected to the primary side of the transformer T, and the drive signal S from the PWM drive circuit is connected to the gate of the transistor Tr. On the secondary side of the transformer T, rectifying and circulating diodes D1 and D2, an inductor L, and a capacitor C are connected. The input DC voltage Vin is converted into a desired DC voltage Vout by adjusting the ON / OFF duty ratio of the transistor Tr.

  In the switching power supply device shown in FIG. 1, a synchronous rectification type power supply in which the diodes D1 and D2 are replaced with switching elements is proposed in Patent Document 1 in order to suppress power loss due to a forward voltage drop of the diodes D1 and D2. ing. According to this, as shown in FIG. 2, the auxiliary winding 4 provided on the secondary side of the conversion transformer T1 and the output of the auxiliary winding 4 are received and arranged between the conversion transformer secondary windings. A forward type DC / DC converter including an FET gate voltage holding circuit 3 for generating a signal for turning on / off the gates of the rectifying FET 2 and the commutating FET 3 is disclosed. Further, Patent Document 2 discloses a technique for obtaining different voltages, for example, 3.3 V and 1.8 V outputs from one input in a synchronous rectification DC-DC converter power supply device.

JP 2004-180386 A JP 2004-208490 A

  As described above, the conventional switching power supply device, as shown in Patent Document 1 and Patent Document 2, reduces power loss by a synchronous rectifier circuit, but improves power factor correction (PFC). It wasn't enough. The reason why synchronous rectification was not used for power factor improvement is that when AC100V (domestic) or AC220V (Europe) is input, the input voltage is boosted to a peak value (approximately 1.4 times the input voltage). This is because the current was not a problem.

  However, the power supply unit connected to the power supply obtained by stepping down the AC power supply becomes a power supply device or power supply system with a large input current (secondary side of the transformer T), and apparent power due to a decrease in power factor cannot be ignored. . For example, as shown in FIG. 3, a power supply system including a transformer 10 that converts an AC power supply of AC 100 V into an AC power supply of AC 24 volts, and a plurality of power supply units 20 to 26 that input the AC 24 V AC power supply generated by the transformer 10. Then, the current Ib supplied to each of the power supply units 20 to 26 is approximately four times (Ib = 4 × Ia) as compared to the current Ia flowing when the AC power supply is 100 V, and if the power factor is low, it is not used effectively. The ratio of apparent power increases.

  The power factor in the rectifier circuit is expressed by the ratio of the active power W and the apparent power VA, that is, W / VA. If the power factor is low, the apparent power VA includes a lot of reactive power that is not effectively used. In normal capacitor input type rectification, the power factor is about 0.6. For this reason, for example, in the power supply system as shown in FIG. 3, assuming that the efficiency is 0.85, the power factor is 0.6, and the power consumption of the load on the output side is 12 V × 5 A, the apparent power VA of the transformer 10 is As shown in Formula (1), it is about 117 VA.

  As a result, the input current of the transformer 10 is 4.875 A as shown in Equation (2). As is clear from the equation (2), the higher the power factor, the smaller the input current from the transformer 10 (current on the secondary side of the transformer 10).

  In the power supply system as shown in FIG. 3, since a plurality of power supply units are connected to the transformer 10, the input current of the transformer 10 is increased by the number of power supply units. As a result, the transformer 10 can be reduced in size. Becomes difficult and the cost becomes high.

  On the other hand, the diode D used for rectification of the power supply units 20 to 26 causes a voltage drop in the forward direction. If the voltage drop is about 0.9V, 0.9V × 4Ia of power is lost. As described above, if the power factor is not improved, the power of 4.875A × 0.9V≈4.4W will be lost in one power supply unit, and the power loss of the entire power supply unit is also considerably large. turn into.

  The present invention has been made to solve the above-described conventional problems, and provides a power supply system capable of improving the power factor as compared with the conventional technique and reducing the size and cost of the power transformer. Objective.

  A power supply system according to the present invention is connected to a transformer for converting a first AC power supply having a first voltage into a second AC power supply having a second voltage lower than the first voltage, And a plurality of power supply units for inputting a second AC power supply of the transformer. Each power supply unit rectifies the second AC voltage of the second AC power source supplied from the transformer and outputs the rectified voltage, and the power factor of the rectified power connected to the rectifier circuit A power factor correction circuit for improving and an output circuit connected to the power factor correction circuit and outputting a DC voltage, the power factor correction circuit being an inductor connected in series to the first voltage line of the rectifier circuit A first transistor connected in series with the inductor, a second transistor connected between a node connecting the inductor and the first transistor, and a second voltage line of the rectifier circuit; And a control circuit that controls switching of the second transistor, and when the second transistor is turned on, the control circuit turns off the first transistor and turns off the second transistor. When, to turn on the first transistor.

  Preferably, the first and second transistors are MOSFETs, the drain of the first transistor is connected to the inductor, the source of the first transistor is connected to the output circuit, and the drain of the second transistor is the first The drain of the transistor is connected, the source of the second transistor is connected to the second voltage line, the gates of the first and second transistors are connected to the control circuit, and a second voltage is applied from the output circuit. A further boosted DC voltage is output.

  Preferably, the first transistor, the second transistor, and the control circuit are housed in one package. In this case, the package includes at least three external terminals, the first external terminal is electrically connected to the drain of the first transistor, and the second external terminal is electrically connected to the source of the first transistor. And the third external terminal is electrically connected to the source of the second transistor.

  More preferably, the first voltage of the first AC power supply is 100 volts, the second AC voltage of the second AC power supply is 24 volts, and the output circuit outputs the DC voltage stepped down by the switching circuit. A DC-DC converter can be included.

  According to the present invention, in the power factor correction circuit, the first and second transistors capable of switching control are used to convert the second AC power source to the DC power source, so that the power factor can be improved. it can. For this reason, the input current of the transformer can be reduced as compared with the conventional one. As a result, the transformer can be reduced in size and cost. Furthermore, the overall power loss of the power system can be reduced by reducing the power consumption of the transistor in the power supply unit compared to that of the diode. Furthermore, by using a device in which the first and second transistors of the power factor correction circuit and the control circuit are packaged, the device can be easily adapted to various power supply units.

  The best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 4 is a diagram showing the configuration of the power supply system according to the embodiment of the present invention. The power supply system 100 includes an insulating power transformer 110 and a plurality of power supply units 200-1 to 200-n (n is a natural number) connected to the power transformer 110. The insulated power transformer 110 preferably inputs commercial AC 100V AC power to the primary side and outputs AC 24V AC power to the secondary side. On the secondary side of the power transformer 110, n power units 200-1 to 200-n are connected, and AC power of 24V AC is supplied to each of the power units 200-1 to 200-n. Such a power supply system is used, for example, in a pachinko game hall, and each play stand has one power supply unit.

  Since the internal configurations of the plurality of power supply units 200-1 to 200-n are substantially the same, the power supply unit 200-1 will be described here. The power supply unit 200-1 includes a rectifier circuit 210 that rectifies the AC 24 V power supply, a power factor correction circuit 220 connected to the rectifier circuit 210, and an output circuit 230 connected to the power factor improvement circuit 220. The

  The rectifier circuit 210 includes, for example, a diode bridge 212 and rectifies an AC 24V AC voltage. The power factor correction circuit 220 includes an inductor L, FET1, FET2, and a control circuit 222. The inductor L is connected in series to the positive power line of the rectifier circuit 212. The drain of FET1 is connected to inductor L at node N1, and the source of FET1 is connected to output circuit 230 at node N3. The drain of the FET2 is connected to the node N1, and the source of the FET2 is connected to the node N2 of the ground line. Control signals S1 and S2 output from the control circuit 222 are connected to the gates of the FET1 and FET2. The control circuit 222 preferably controls the switching of FET1 and FET2 at an appropriate frequency and duty ratio to bring the power factor close to 1.0.

  The output circuit 230 includes an electric field capacitor C connected between the node N3 and the ground line, and an output terminal Vout that outputs a DC voltage. By the switching control of the control circuit 222, a DC voltage boosted to about 34V is output from the output terminal Vout. If necessary, the output circuit 230 can include DC / DC converters 232 and 234 that step down the DC voltage of Vout. The converters 232 and 234 convert the output voltage into, for example, a DC voltage of 12V and 5V. The

  Next, the operation of the power supply system will be described. The 24V AC power converted by the power transformer 110 is supplied to each of the power supply units 200-1 to 200-n. The 24V AC voltage is rectified by the rectifier circuit 210, and the rectified power is input to the power factor correction circuit 220.

  The control circuit 222 adjusts the duty ratio of the FET1 and FET2 by the control signals S1 and S2, accumulates electric energy in the inductor L, and supplies the accumulated energy to the capacitor C. That is, when the control circuit 222 turns on the FET 2, the control circuit 222 turns off the FET 1 and accumulates energy in the inductor L. Next, when the FET 2 is turned off, the FET 1 is turned on, and the energy accumulated in the inductor L is output to the capacitor C. As a result, a DC voltage of about 32 V is output from the output terminal Vout.

  In this embodiment, the power factor improvement circuit 220 is provided in the power supply unit, and the power factor is brought close to 1.0, so that the apparent power of this embodiment is compared with the apparent power VA shown in the conventional formula (1). VA is 70.5 VA as shown in Equation (3). The input current (secondary side current) from the transformer 110 is 2.937 A, as shown in Expression (4).

  As described above, although the efficiency is somewhat reduced by inserting the power factor correction circuit 220, on the other hand, the input current of the transformer 110 can be reduced to about half, and the transformer 110 can be reduced in size and cost. be able to.

  Further, by using a rectifying transistor instead of a conventional rectifying diode, power loss due to the diode (power loss = 0.9V × 5A = 4.5 W when the voltage drop is 0.9 V and the current is 5 A) On the other hand, the power loss due to the transistor (power loss = 0.005Ω × 5A × 5A = 1.25 W when the on-resistance is 0.005Ω and the current is 5 A) can be reduced. Since the on-resistance tends to be smaller as the source-drain breakdown voltage of the FET is smaller, if the breakdown voltage is about 34 volts as in this embodiment, an FET with a lower on-resistance should be used. Can do.

  The control circuit 222 included in the power factor correction circuit 220 can use a known PWM control circuit. For example, by monitoring the switching current, output voltage, output current, etc. of the FET, the frequency of the FET1, FET2 is monitored. And the duty ratio can be adjusted.

  Next, a second embodiment of the present invention will be described. In the power factor correction circuit 200 shown in FIG. 4, since the source-drain voltage of FET1 and FET2 is as small as about 34 V, an FET with a lower withstand voltage can be used, and the FET can be downsized. . As a result, the FET1, FET2, and control circuit 222 used in the power factor correction circuit can be packaged in one semiconductor device.

  FIG. 5 is a diagram illustrating a configuration example of a semiconductor device in which a part of the power factor correction circuit (excluding the inductor L) is packaged. A semiconductor device 300 shown in FIG. 5 includes a package main body 310, three external terminals 320, 322, and 324 that protrude from the lower portion of the package main body 310, and a heat sink 330. In the package main body 310, the control circuit 222, FET1, and FET2 shown in FIG. 4 are placed on a die pad, and these are sealed with resin. The external terminals 320, 322, and 324 are connected to electrode pads on the die pad by bonding wires or the like. Thereby, the external terminal 320 is electrically connected to the node N1 shown in FIG. 4, the external terminal 322 is electrically connected to the node N2, and the external terminal 324 is electrically connected to the node N3. Thus, by packaging the power factor correction circuit in the semiconductor device 300, the power factor correction circuit can be easily connected to the power supply system, and the power factor of various power supply systems can be easily improved. .

  5 shows the semiconductor device 300 having a three-terminal structure, but the semiconductor device 302 may have four terminals including an external terminal 326 as shown in FIG. For example, the external terminal 326 can supply an external control signal for switching on / off of the control circuit 222 to the control circuit 222.

  Further, the semiconductor device 304 may have five terminals including an external terminal 328 as shown in FIG. In this case, the external terminal 328 can be used for voltage adjustment of the output voltage Vout, and functions as an external terminal for supplying the output voltage Vout to the control circuit 222. Of course, this voltage adjustment function is not necessarily executed in the five-terminal semiconductor device 304, but may be executed in the four-terminal semiconductor device 302 as shown in FIG.

  Furthermore, the semiconductor devices 300, 302, and 304 shown in FIG. 5 and FIGS. 6A and 6B are attached in such a manner that the external terminals stand upright on the substrate. In this manner, the external terminals 320, 322, and 324 (326 and 328) may be bent so that the package body can be surface-mounted so that the package body contacts the circuit board or the like.

  The power supply system according to the present invention can be used in a synchronous rectification type power supply device with improved power factor.

It is a figure which shows the structure of the conventional switching power supply device. It is a figure which shows the structure of the conventional synchronous rectification type switching power supply device. It is a figure explaining the subject of the conventional switching power supply device. It is a figure which shows schematic structure of the synchronous rectification type | mold power supply system which concerns on the Example of this invention. It is a figure which shows the structural example of the semiconductor device which packaged the power factor improvement circuit of the power supply system which concerns on 2nd Example of this invention. 6A illustrates an example of a four-terminal semiconductor device, and FIG. 6B illustrates an example of a five-terminal semiconductor device. It is a figure which shows the example which surface-mounts a semiconductor device.

Explanation of symbols

100: power system 110: power transformer 200-1 to 200-n: power unit 210: rectifier circuit 220: power factor correction circuit 222: control circuit 230: output circuits 300, 302, 304: semiconductor device 310: package body 320, 322, 324, 326, 328: External terminals

Claims (6)

A transformer for converting a first AC power source having a first voltage into a second AC power source having a second voltage lower than the first voltage, and a second AC power source connected to the transformer, Including a plurality of power supply units to input,
Each power supply unit rectifies the second AC voltage of the second AC power supplied from the transformer, and outputs a rectified voltage;
A power factor correction circuit connected to the rectifier circuit to improve the power factor of the rectified power;
An output circuit connected to the power factor correction circuit and outputting a DC voltage;
The power factor correction circuit includes an inductor connected in series to the first voltage line of the rectifier circuit, a first transistor connected in series to the inductor, a node connecting the inductor and the first transistor, and rectification A second transistor connected between the second voltage line of the circuit and a control circuit for controlling switching of the first and second transistors, the control circuit turning on the second transistor; When turning off the first transistor and turning off the second transistor, turn on the first transistor,
Power system. The first and second transistors are MOSFETs, the drain of the first transistor is connected to the inductor, the source of the first transistor is connected to the output circuit, and the drain of the second transistor is the drain of the first transistor. , The source of the second transistor is connected to the second voltage line, the gates of the first and second transistors are connected to the control circuit, and the output circuit boosts the voltage from the second voltage. The power supply system according to claim 1, wherein a direct current voltage is output. The power supply system according to claim 1, wherein the first transistor, the second transistor, and the control circuit are housed in one package. The package includes at least three external terminals, the first external terminal is electrically connected to the drain of the first transistor, and the second external terminal is electrically connected to the source of the first transistor. The power supply system according to claim 3, wherein the third external terminal is electrically connected to the source of the second transistor. The power supply system according to claim 1, wherein the first voltage of the first AC power supply is 100 volts, and the second AC voltage of the second AC power supply is 24 volts. The power supply system according to claim 1, wherein the output circuit includes a DC-DC converter that generates a direct-current voltage stepped down by a switching circuit.

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