JP2005295649A - Switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable stabilized switching power supply in which a relay contact is not deteriorated substantially and an inrush current can be suppressed by a small relay. <P>SOLUTION: Immediately after the throw-in of an AC input voltage VAC, a relay contact 17 constituting an inrush current control circuit 10 is in an off-state, and an inrush current flowing into a step-up converter 5 is suppressed. Since the inrush current control circuit 10 is connected with the ground line between the step-up converter 5 and a smoothing capacitor 7, a voltage applied across the relay contact 17 becomes 0 volt. When the inrush current is converged and the relay contact 17 is turned on, the power consumption of the relay contact 17 is decreased because the output current from the step-up converter 5 is low, and thereby sufficient reliability and stability can be secured even if an inexpensive small relay is used. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a switching power supply device, and more particularly to a switching power supply device including a circuit that suppresses an inrush current when power is turned on.

  As a DC power supply for various electronic devices, a switching power supply is often used that supplies a DC voltage obtained by rectifying and smoothing an AC input voltage from a commercial power supply to a desired DC voltage by a DC / DC converter. Has been. For voltage adjustment, a transformer in which the DC voltage is intermittently applied to the primary winding is often used.

  There is also known a switching power supply device in which a commercial power supply is rectified by a rectifier circuit such as a diode bridge and a boost converter for power factor improvement is provided on the output side of the rectifier circuit.

  FIG. 2 shows an example of a conventional switching power supply device. As shown in the figure, the AC input voltage VAC from the commercial power source 2 is full-wave rectified by a bridge type rectifier 4 and this rectified output is applied to the boost converter 5. The step-up converter 5 includes a choke coil 11, a switching element 12, and a rectifier diode 13. In principle, the output voltage from the step-up converter 5 is smoothed by the smoothing capacitor 7 and connected between both ends of the smoothing capacitor 7. The boosted DC voltage Vo is output from the output terminals 21 and 22 to a subsequent DC / DC converter (not shown). Actually, the switching element 12 is a transistor, FET or the like, and the control device 8 variably controls the conduction width of the pulse drive signal supplied to the switching element 12 in accordance with the fluctuation of the DC voltage Vo.

  In the power supply device having the above configuration, since the switching element 12 is in the OFF state when the power is turned on, the voltage that has been full-wave rectified by the bridge type rectifier 4 is applied to the smoothing capacitor 7 through the choke coil 11 and the rectifier diode 13. A large inrush current flows. This rush current may cause deterioration of the rectifier diode 13 and the smoothing capacitor 7.

  In order to solve such a problem, as shown in FIG. 3, a circuit that suppresses inrush current by inserting a power thermistor 6 between a boost converter 5 and a smoothing capacitor 7 has been proposed (for example, Patent Document 1). 1). Here, the operation of the power thermistor 6 will be described below. When the power is first turned on, the temperature of the power thermistor 6 is low and its resistance value is high. Therefore, since the resistance of the power thermistor 6 enters the smoothing capacitor 7 in series, an inrush current can be suppressed. Eventually, when an input current flows through the voltage supply line of the boost converter 5 and the smoothing capacitor 7 is charged, the control device 8 for driving the switching element 12 is activated and the switching element 12 starts operating normally. Then, power is supplied to the subsequent DC / DC converter, and the temperature of the power thermistor 6 rises. When the temperature of the power thermistor 6 rises, its resistance value decreases, and when it reaches a certain resistance value, its power consumption and temperature are balanced and stabilized.

  However, such a circuit has the following drawbacks. For example, in the case of a so-called instantaneous power failure in which the commercial power supply is restored immediately after a power failure, the smoothing capacitor 7 discharges instantaneously, but the temperature of the power thermistor 6 does not decrease instantaneously, so the resistance value remains low. There is a problem that the power is turned on again in a state and a large inrush current flows.

  FIG. 4 shows another conventional example for avoiding such a problem. In the example shown in FIG. 4, a parallel circuit composed of a resistor 16 and a switching element 17 is inserted as the inrush current suppression circuit 10 between the commercial power source 2 and the bridge type rectifier 4. Here, as the switching element 17, each element such as a thyristor, an FET, a transistor, a triac, and a relay contact can be used. Here, a power-on monitoring circuit 9 is provided to monitor the output voltage Vo generated on the output side of the smoothing capacitor 7 or the voltage from the secondary winding (not shown) inductively coupled to the choke coil 11, When a certain time elapses after the power is turned on, a driving signal for turning on the switching element 17 is supplied to the switching element 17. The capacitor 18 is not a smoothing capacitor, but a small-capacitance capacitor for removing noise.

  The operation of the inrush current suppression circuit 10 will be described below. When the power source is turned on from the commercial power source 2, the switching element 17 is turned off, so that the inrush current flows into the boost converter 5 through the resistor 16, and the current to the boost converter 5 is the resistance of the inrush current suppression circuit 10. Limited by 16. When the smoothing capacitor 7 is charged and the output voltage Vo rises, the switching element 17 is turned on by the drive signal from the power-on monitoring circuit 9, and the input current flows through the switching element 17 side and flows through the boost converter 5. After that, it is supplied to the output side.

Here, when a semiconductor element such as a thyristor, FET, transistor, or triac is used as the switching element 17, a voltage drop occurs during conduction. Therefore, the switching element 17 is equivalent to the product of the voltage and current of the voltage drop. The power becomes a loss in the steady state, which reduces the efficiency of the power source. In this regard, when a relay contact is used as the switching element 17, there is almost no such voltage drop, and there is no loss in the inrush current suppression circuit 10 in a steady state.
Japanese Patent Laid-Open No. 2001-309652

  In the configuration shown in FIG. 4, an AC input voltage VAC is applied to one end of the relay contact. Until this relay contact is turned on, an AC current is at most between one end and the other end of the relay contact. A voltage twice the peak value of input voltage VAC (1.4 times VAC) is applied. In addition, even after the relay contact is turned on, when the AC input voltage VAC is low, the input current flowing through the relay contact increases accordingly, so that loss (power consumption) increases and it is likely to cause a power failure. Therefore, in order to avoid such a problem, there has been a concern that the relay becomes large and expensive.

  An object of the present invention is to provide a stable and reliable switching power supply that can suppress inrush current with a small-sized relay by using an inrush current suppression circuit configured by parallel connection of a resistor and a relay contact, with almost no deterioration of the relay contact. To provide an apparatus.

  The present invention provides a rectifier circuit for rectifying an AC input voltage, a boost converter on the output side of the rectifier circuit for improving the power factor by bringing the waveforms of the AC input voltage and the input current close to each other, and the boost converter In a switching power supply device comprising a smoothing capacitor for smoothing the output voltage, an inrush current suppression circuit comprising a resistor and a relay contact connected in parallel to a ground line between the boost converter and the smoothing capacitor is provided. Composed.

  In this case, immediately after the AC input voltage is applied, the relay contact that constitutes the inrush current suppression circuit is in the off state, so that the inrush current that flows into the boost converter via the rectifier circuit is suppressed, and the rectifier circuit or There is no deterioration of the smoothing capacitor. Further, since the inrush current suppression circuit is inserted and connected to the ground line between the boost converter and the smoothing capacitor, the voltage applied across the relay contact is 0 volts. After that, in a steady state where the inrush current converges and the relay contact is switched on, the voltage output from the boost converter is high, but the current output from the boost converter is small, so the power consumption of the relay contact is reduced. Even when a small and inexpensive relay is used, sufficient reliability and stability can be ensured.

  According to the present invention, by using an inrush current suppression circuit configured by parallel connection of a resistor and a relay contact, there is almost no deterioration of the relay contact, and a stable and reliable switching power supply that can suppress the inrush current with a small relay. Equipment can be provided.

  Hereinafter, a preferred embodiment of the switching power supply device of the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the location which has the substantially same function as a prior art example.

  According to the example shown in FIG. 1, the AC input voltage VAC from the commercial power source 2 is full-wave rectified by the bridge-type rectifier 4, and the rectified output is input to the boost converter 5. Is smoothed by the smoothing capacitor 7 and the DC voltage Vo is output from the output terminals 21 and 22. More specifically, boost converter 5 has a series circuit including choke coil 11 and switching element 12 connected to the output terminal of rectifier 4, and an anode connected to a connection point between choke coil 11 and switching element 12. The smoothing capacitor 7 which is constituted by the rectifier diode 13 and which is on the output side of the boost converter 5 is between the cathode of the rectifier diode 13 and the negative output end of the rectifier 4 to which the other end of the switching element 12 is connected. Connected. Further, the control device 8 variably controls the conduction width of the pulse drive signal supplied to the switching element 12 in accordance with the fluctuation of the DC voltage Vo. The capacitor 18 connected between the output terminals of the rectifier 4 has a noise removal function. This is a small-capacitance capacitor. The above configuration is the same as that shown in the conventional example.

  On the other hand, the inrush current suppression circuit 10 according to the present invention is not connected to the AC input voltage VAC line extending from the commercial power source 2 to the rectifier 4 but to the ground between the other end of the switching element 12 constituting the boost converter 5 and the smoothing capacitor 7. Note that it is inserted and connected to the line. This inrush current suppression circuit 10 is composed of a parallel circuit of a resistor 16 and a relay contact 17, and the relay contact 17 is normally open, so that an inrush current flows through the resistor 16 when the power is turned on, and the rectifier diode 13 and the smoothing capacitor 7 are not deteriorated. Similarly to the conventional example, the power-on monitoring circuit 9 monitors the output voltage Vo generated on the output side of the smoothing capacitor 7 or the voltage from the secondary winding (not shown) inductively coupled to the choke coil 11 to A relay drive signal for turning on the relay contact 17 is supplied to the relay contact 17 when a certain time has elapsed after being turned on.

  Next, the operation of the above configuration will be described.

  When power is turned on from the commercial power source 2, the AC input voltage VAC is full-wave rectified by the bridge-type rectifier 4, and the rectified output from the rectifier 4 is applied to the boost converter 5. Immediately after the power is turned on, the step-up converter 5 is charged to the smoothing capacitor 7 from the choke coil 11 of the step-up converter 5 through the rectifier diode 13 because the switching element 12 is in the OFF state. Further, the relay contact 16 immediately after power-on is not supplied with a relay drive signal from the power-on monitoring circuit 9 and is in an off state. At this time, if the inrush current suppression circuit 10 is not provided, a large inrush current flows through the boost converter 5 and the rectifier diode 13 and the smoothing capacitor 7 are deteriorated. In this embodiment, the boost converter 5 and the smoothing capacitor 7 Since the current passes through the resistor 16 of the inrush current suppression circuit 10 inserted and connected to the ground line between them, a large inrush current is suppressed by the resistor 16 and the rectifier diode 13 and the smoothing capacitor 7 are not deteriorated. . The voltage applied across the relay contact 17 is 0 volts because the relay contact 17 is connected to the ground line, and a high voltage is applied across the relay contact 17 when the relay contact 17 is off. There is no fear.

  When time passes and charging of the smoothing capacitor 7 proceeds, the output voltage Vo across the smoothing capacitor 7 increases. Along with this, the control device 8 for driving the switching element 12 is activated to start the on / off operation of the switching element 12 and to prevent power loss due to the current continuously passing through the resistor 16. The relay contact 17 is switched to the ON state by the drive signal from the power-on monitoring circuit 9, and the current output from the boost converter 5 passes through the relay contact 17 having a resistance value smaller than that of the resistor 16.

  When the switching element 12 of the step-up converter 5 is turned on by the drive pulse from the control device 8, the rectified output generated from the rectifier 4 is applied across the choke coil 11, and a current flows through the choke coil 11 to generate energy. Accumulated. Thereafter, when the switching element 12 is turned off, an induced electromotive force is generated by the energy accumulated in the choke coil 11, and a boosted voltage obtained by superimposing the induced electromotive force and the voltage generated from the rectifier 4 is supplied from the boost converter 5. Given to the smoothing capacitor 7, the smoothing capacitor 7 is charged. By repeating this operation, the current flowing from the commercial power source 2 through the rectifier 4 and flowing through the choke coil 11 becomes a triangular wave, and the current peak becomes a value proportional to the AC input voltage VAC. The peak envelope follows the waveform of the AC input voltage VAC, and the power factor is improved.

  In a series of operations in the steady state, a current flows through the relay contact 17 between the boost converter 5 and the smoothing capacitor 7. The current output from the boost converter 5 is supplied from the commercial power source 2 to the rectifier 4. Even when the AC input voltage VAC is lower than the input current flowing into the step-up converter 5 via, the power loss of the relay contact 17 is small. Therefore, it is possible to cope with a smaller relay than that of the conventional example, and it is possible to reduce the size of components and to provide the inrush current suppressing circuit 10 with low power consumption.

  As described above, in this embodiment, the rectifier 4 as a rectifier circuit for rectifying the AC input voltage VAC and the output side of the rectifier 4 are arranged so that the waveforms of the AC input voltage VAC and the input current are brought close to each other. In a switching power supply device including a boosting converter 5 to be improved and a smoothing capacitor 7 that smoothes a boosted voltage output from the boosting converter 5, a resistor is connected to a ground line between the boosting converter 5 and the smoothing capacitor 7. An inrush current suppression circuit 10 in which 16 and a relay contact 17 are connected in parallel is provided, and the relay contact 17 is switched from OFF to ON when a certain time has elapsed after the AC input voltage VAC is applied.

  In this case, immediately after the AC input voltage VAC is turned on, the relay contact 17 constituting the inrush current suppression circuit 10 is in an OFF state, so that the inrush current that flows into the boost converter 5 via the rectifier 4 is suppressed. The rectifier 4 and the smoothing capacitor 7 are not deteriorated. Further, since the inrush current suppression circuit 10 is inserted and connected to the ground line between the boost converter 5 and the smoothing capacitor 7, the voltage applied across the relay contact 17 becomes 0 volts. Thereafter, in a steady state in which the inrush current converges and the relay contact 17 is switched on, the voltage output from the boost converter 5 is high, but the current output from the boost converter 5 is small. Electricity is reduced, and even when a small and inexpensive relay is used, sufficient reliability and stability can be ensured.

  In addition, this invention is not limited to said Example, A various deformation | transformation implementation is possible in the range of the summary of this invention. For example, the circuit configuration of the boost converter 5 in the embodiment is merely an example, and may be replaced with one that exhibits a similar function.

1 is a circuit diagram showing a preferred embodiment of a switching power supply device according to the present invention. It is a circuit diagram explaining the principle of the switching power supply device in a prior art example. It is a circuit diagram of the switching power supply device provided with the inrush current suppression circuit in a prior art example. It is another circuit diagram of the switching power supply device provided with the inrush current suppression circuit in a prior art example.

Explanation of symbols

4 Rectifier (rectifier circuit)
5 Boost Converter 7 Smoothing Capacitor 8 Control Device
10 Inrush current suppression circuit
16 resistance
17 Relay contact

Claims (1)

A rectifier circuit for rectifying an AC input voltage, a boost converter on the output side of the rectifier circuit for improving the power factor by bringing the waveforms of the AC input voltage and the input current closer, and smoothing the output voltage of the boost converter A switching power supply including a smoothing capacitor that includes a rush current suppression circuit in which a resistor and a relay contact are connected in parallel to a ground line between the boost converter and the smoothing capacitor. Switching power supply.

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