JP2008079380A - Power supply unit and power supply system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To supply a power supply unit and a power supply system which stabilize the ground potential of electronic equipment relative to grounding to enhance the stability of the electronic equipment and to suppress the generation of noises. <P>SOLUTION: Capacitor input type rectifying/smoothing circuits are constituted of a rectifying circuits 2 for inputting a commercial AC power supply AC for rectification and a smoothing circuit 3 to supply DC voltage to a DC-DC converter 4 and capacitors C1 to C4 are connected in parallel to four diodes D1 to D4 in the rectifying circuit 2 as a full-wave rectification diode bridge circuit. The diodes D1 to D4 are energized only near the peak voltage of the commercial AC power supply and the ground potential is grounded via the capacitors C1 to C4, allowing the ground potential of the electronic equipment to be stabilized for prevention of the generation of noises and improvement in the stability in circuit operation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power supply apparatus that inputs a commercial AC power supply and supplies a DC power supply voltage to an electronic device, and a power supply system including the power supply apparatus.

  In general, a power supply device for a small electronic device that operates at a low voltage of about 5 to 25 V, for example, directly rectifies and smoothes a commercial AC power supply with a diode and a capacitor, and converts the voltage to a predetermined voltage with a DC-DC converter. It is configured to descend. Such a power supply device is configured as an AC adapter or incorporated in an electronic device.

  Here, a configuration example of a conventional power supply apparatus is shown in FIG. The power supply device 110 includes an EMI filter 1, a rectifier circuit 2, a smoothing circuit 3, and a DC-DC converter 4. Commercial AC power is input to the input terminal IN. The rectifier circuit 2 rectifies the commercial AC power input through the EMI filter 1, and the smoothing circuit 3 smoothes it. The DC-DC converter 4 drops the voltage of the smoothing circuit 3 to a predetermined voltage and outputs it to the output terminal OUT.

  On the other hand, in general homes in Japan, there are almost only two AC outlets, and it is difficult to ground the frame ground of the electronic device to the ground. In addition, since an AC adapter of a portable electronic device such as a notebook personal computer is important for portability and is not provided with a ground terminal, the frame ground is not grounded even in an office building compatible with OA (see, for example, Patent Document 1).

Therefore, there are many scenes where the frame ground of the electronic device is used in a state where it is floating with respect to the ground potential. Patent document 1 aims at reduction of the leakage current when a human touches an electronic device under such a situation. In Patent Document 1, a capacitor (Y capacitor) is provided between a voltage dividing point by two capacitors inserted in series with a commercial AC power supply line and a secondary side of a transformer of a DC-DC converter. It is intended to reduce the potential difference between the frame and the ground.
JP 2001-238439 A

  However, in the power supply apparatus in which the frame ground of the power supply apparatus is not grounded and commercial AC power is directly rectified and smoothed and supplied to the DC-DC converter, the following problems occur.

  First, as already mentioned, the commercial AC power supply in Japan is generally a two-wire system with one side grounded, and since the ground wire is not drawn, the ground wire is specially drawn and the outlet is 3 poles. Frame grounding is not done unless it is a formula. Therefore, as shown in Patent Document 1, the human body touches the frame (metal part) of the electronic device to be grounded through the human body, thereby determining the ground potential, so that the human body touches the frame part. / Depending on the usage environment such as not touching, the potential of the frame ground relative to the ground varies depending on the equivalent impedance (high resistance + capacitance component) between the electronic device and the human body. Moreover, the equivalent impedance varies depending on the situation. This adversely affects the operational stability of the electronic device.

  Also, in a so-called capacitor input type power supply device that rectifies and smoothes commercial AC power, the conduction period of the diode during one cycle of the commercial AC power is short, and 1 of the DC-DC converter is in a period in which the diode is in a reverse bias state. Even when the secondary side (also the secondary side) is floating from the ground and the human body is touching the frame portion, the ground potential becomes unstable (fluctuates) every period of the commercial AC power supply frequency. For this reason, for example, there is a problem that noise occurs when an electronic device as a load is a device that handles an audio signal such as a telephone.

  An object of the present invention is to solve the above-described problems, and to provide a power supply device and a power supply system that stabilize the ground potential of an electronic device with respect to grounding, increase the stability of the electronic device, and suppress the generation of noise. It is in.

  The present invention provides a rectifier circuit that rectifies a commercial AC power supply, a smoothing circuit that smoothes the output voltage of the rectifier circuit, generates a DC voltage of a predetermined voltage by inputting the output voltage of the smoothing circuit, and a load. In the power supply apparatus including the DC-DC converter to be supplied to the rectifier, the rectifier circuit is configured by a rectifier diode and a capacitor connected in parallel to the rectifier diode, and the capacitance of the capacitor is reversed from that of the rectifier diode. It is characterized in that the current flows for a sufficiently long period compared to the conduction period of the rectifier diode at the time of bias.

  The rectifier circuit is, for example, a full-wave rectifier diode bridge circuit including four diodes, and the capacitors are connected in parallel to at least two of the four diodes on the positive voltage output side or the negative voltage output side.

  The power supply system of the present invention includes the power supply device and its load, and neither the power supply device nor the frame of the load is grounded, and the load is an electronic device that handles an audio signal.

  According to the present invention, the capacitor is connected in parallel to the rectifier diode, and when the rectifier diode is reverse-biased, the current flows for a period sufficiently longer than the conduction period of the rectifier diode. In addition, a small amount of current flows through the capacitor, and grounding through the line on the ground side stabilizes the high-frequency ground potential of the electronic device. Therefore, the ground potential does not fluctuate between the state in which the human body is in contact with the frame (metal part) of the electronic device and the state in which the human body is not in contact, generation of noise can be suppressed, and the stability of the circuit operation is increased.

  Note that if the capacitance of the capacitor connected in parallel with the diode is too large, the rectification / smoothing effect will be significantly reduced when the diode is reverse-biased. The problem does not arise by determining the capacitance of the capacitor so that the charging current flows for a period sufficiently shorter than a half cycle. Further, since a small capacitor can be used, the apparatus size does not increase.

  FIG. 2 is a diagram showing a configuration of a power supply device and a power supply system including the same according to an embodiment of the present invention. The power supply device 100 includes an EMI filter 1, a rectifier circuit 2, a smoothing circuit 3, and a DC-DC converter 4. A commercial AC power supply AC is input to the power supply apparatus 100, and an IP telephone router 200 and a telephone 210 are connected to the output as electronic devices in this example. A communication line 201 such as a telephone line and a LAN cable is connected to the IP telephone router 200.

  In the example shown in FIG. 2, the power supply device 100 has a so-called AC adapter shape, but this power supply device may be incorporated in an electronic device such as an IP telephone router.

  The EMI filter 1 includes a common mode choke, a normal mode choke, a line bypass capacitor, an across-the-line capacitor, and the like. Controls the outflow of noise to commercial AC power.

  In the rectifier circuit 2, four diodes D1 to D4 are bridge-connected, and capacitors C1 to C4 are connected in parallel to the respective diodes. The commercial AC power supply voltage is full-wave rectified by this full-wave rectifier diode bridge circuit.

  The capacitances of the capacitors C1 to C4 are determined so that a current flows for a period sufficiently longer than the conduction periods of the rectifier diodes D1 to D4 when the rectifier diodes D1 to D4 are reversely biased. For example, it may be as small as several tens of pF to several μF.

  The smoothing circuit 3 is composed of a smoothing capacitor, and is set to a value such that the time constant determined by the resistance component of the line and the capacitance of the smoothing capacitor is sufficiently larger than the half wavelength of the commercial AC power supply frequency. In addition, the smoothed output voltage is set to be equal to or higher than a predetermined voltage in the event of an instantaneous power failure. Therefore, a capacitor input type rectifying and smoothing circuit is formed together with the rectifying circuit 2.

  In the DC-DC converter 4, a switching element Q1 is connected in series to the primary winding N1 of the converter transformer T1, and a rectifying and smoothing circuit including a diode D12 and a capacitor C12 is connected to the secondary winding N2. Further, the secondary side ground and the primary side ground of the converter transformer T1 are connected by a capacitor C13. This capacitor C13 is provided as a line bypass capacitor. That is, the negative output terminal of the power supply apparatus 100 is connected to the ground (frame ground) in the IP telephone router 200. The control circuit SC switches the switching element Q1 to intermittently pass the current flowing through the primary winding N1 of the converter transformer T1, and the voltage induced in the secondary winding N2 is rectified by the diode D12 and thereby the capacitor C12. Smoothed. Thus, a so-called flyback type DC-DC converter is configured.

  3E is an operation waveform diagram of the rectifier circuit 2 of the power supply device 100 shown in FIG. 2, and FIGS. 3A to 3D are operation waveform diagrams of the rectifier circuit in the power supply device having other circuit configurations. It is. Specifically, in FIGS. 3A to 3E, the upper waveform is a voltage waveform between terminals of one diode, and the lower waveform is a current waveform flowing on the input side of the rectifier circuit.

  FIG. 3A is a waveform diagram in a state where none of the capacitors C1 to C4 is provided in the rectifier circuit 2, and FIG. 3B is a case where only C1 and C2 are provided among the four capacitors C1 to C4. FIG. 3C is a waveform diagram when only C1 and C3 are provided among the four capacitors C1 to C4, and FIG. 3D is a diagram showing only C2 and C4 of the four capacitors C1 to C4. A waveform diagram when provided, (E) is a waveform diagram when all four capacitors C1 to C4 are provided.

Here, the reason why the voltage waveform shown in FIG. 3A is obtained when none of the capacitors C1 to C4 is provided in the rectifier circuit 2 will be described with reference to FIG.
FIG. 4A is a diagram showing the relationship among the commercial AC power supply voltage Vin, the voltage Vd applied to the diode of the input rectifier circuit, and the charging voltage Vc3 of the smoothing capacitor.

  Due to the relationship Vd = Vc3-Vin, the voltage Vd between terminals of any rectifier diode is Vd = 0 (more precisely,-(forward voltage drop)) only during the period when the current Id flows through the diode. It is. In FIG. 4B, Vd indicates the state.

  However, actually, as shown in FIG. 4C, the period in which Vd is 0 extends beyond the period in which Id flows. This is due to the following.

  First, the voltages Vin and Vc3 are not affected by the presence or absence of a capacitor connected in parallel to the rectifier diode. Therefore, when considering the relationship of Vd = Vc3-Vin, the waveform does not change.

  However, if the ground potential and the ground potential of the power supply fluctuate with time, the Vd waveform changes. That is, as shown in FIG. 4C, it is considered that the cause is that the ground and the ground of the power supply are shifted.

  Now, since the rectifying / smoothing circuit of the power supply apparatus shown in FIG. 2 is a capacitor input type, as shown in FIG. 3, current flows through the rectifying circuit 2 only near the peak voltage of the commercial AC power supply voltage, and the capacitors C1 to C4. Is not present, the input side of the DC-DC converter 4 is in a state of floating from the ground during the period in which all of the diodes D1 to D4 are off, and as shown in FIG. Has a certain potential with respect to the ground, and the ground potential fluctuates with the period of the commercial AC power supply frequency. The voltage waveform is distorted from the sine wave due to the fluctuation of the ground potential. It can be inferred that the distortion of the voltage waveform in FIG.

  On the other hand, when four capacitors C1 to C4 are provided, the voltage between the input power supply lines of the rectifier circuit 2 is substantially a sine wave as shown in FIG. This current waveform is close to the current waveform shown in FIG. By connecting the capacitor in parallel with the rectifier diode in this way, a very small current always flows, and as a result, it can be inferred that the ground potential of the power supply is stable. In addition, since the generation of high-frequency noise due to distortion of the voltage between the terminals of the diode is suppressed, it is considered that a further noise reduction effect can be obtained.

  Further, as shown in FIGS. 3C and 3D, even when a capacitor is connected in parallel only to two diodes on the + output or −output side from the input line of the rectifier circuit, the distortion of the sine wave is reduced and the ground is reduced. It can be seen that there is a potential stabilizing effect.

  As shown in FIG. 3B, when a capacitor is connected in parallel to two diodes of + output and −output from one side of the input line of the rectifier circuit, the voltage waveform is affected by the unbalance of the rectifier circuit. Appears to be more distorted than in the case of (A). Therefore, it can be indirectly estimated that the stability of the ground potential of the electronic device (IP telephone router) is improved and the noise reduction effect is low.

  In this way, the highest noise reduction effect can be obtained when capacitors are connected in parallel to all four diodes D1 to D4, but a certain amount of noise reduction effect can be obtained even if capacitors are connected in parallel to at least two diodes. .

  In this embodiment, an example of a flyback system is given as the DC-DC converter 4, but the same effects can be obtained even with a forward converter system, push-pull system, half-bridge system, full-bridge system, or the like.

It is a figure which shows the structure of the conventional power supply device. It is a figure which shows the structure of the power supply device and power supply system which concern on embodiment of this invention. FIG. 3 is a waveform diagram of an input side voltage and an input side current of the rectifier circuit 2 shown in FIG. 2 and a diagram showing a change in waveform depending on whether or not capacitors C1 to C4 are connected. It is a wave form diagram which shows the effect | action of the capacitor | condenser connected to a rectifier circuit.

Explanation of symbols

1-EMI filter 2-rectifier circuit 3-smoothing circuit 4-DC-DC converter 100, 110-power supply device 200-electronic device (load)
201-communication line 210-telephone AC-commercial AC power supply C1-C4-capacitor D1-D4-diode

Claims (3)

A rectifying circuit that rectifies by inputting a commercial AC power supply, a smoothing circuit that smoothes the output voltage of the rectifying circuit, and a DC that generates the DC voltage of a predetermined voltage by inputting the output voltage of the smoothing circuit and supplies the DC voltage to the load A power supply device comprising a DC converter,
The rectifier circuit includes a rectifier diode and a capacitor connected in parallel to the rectifier diode, and the capacitance of the capacitor is a period sufficiently longer than the conduction period of the rectifier diode when the rectifier diode is reverse-biased. A power supply device characterized in that a current flows over the entire area.   The rectifier circuit is a full-wave rectifier diode bridge circuit including four diodes, and the capacitor is connected in parallel to at least two diodes on the positive voltage output side or the negative voltage output side among the four diodes. The power supply described. A power supply system comprising the power supply device according to claim 1 and the load,
The power supply system for an electronic device, wherein neither the power supply device nor the frame of the load is grounded, and the load is an electronic device that handles an audio signal.

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