JP2012120258A - Power-factor improvement circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance safety by restricting generation of an excessive short-circuit current during a short circuit between terminals of an auxiliary winding forming an inductor and preventing a temperature rise in the auxiliary winding.SOLUTION: Between a zero current detection circuit 101 for detecting that energy stored in an inductor 5 is emitted based on an induced voltage from a main winding 50 forming the inductor 5 to an auxiliary winding 51 and the auxiliary winding 51, there is serially connected a protective resistance R3 which restricts an excessive short-circuit current generated during a short circuit caused by substrate corrosion or the like between terminals P1 and P2 of the auxiliary winding 51 to prevent a temperature rise in the auxiliary winding.

Description

  The present invention relates to a power factor conversion circuit used for a switching power supply, and more particularly to a power factor improvement circuit with improved safety.

  Conventionally, as this type of switching power supply device, an AC power source is generally rectified and smoothed by an input rectifying and smoothing circuit to convert it to a DC voltage, and this DC voltage is intermittently switched by a switching element, and the switching output obtained by intermittently is obtained. It is known that an arbitrary DC output voltage is obtained by supplying to an output rectifying / smoothing circuit and rectifying / smoothing.

  In such a switching power supply device, if the smoothing circuit on the input side is a capacitor input type, the input current flows only during a period when the rectified voltage is higher than the charging voltage of the input smoothing capacitor, and there is a difficulty in reducing the power factor. there were. In order to solve this difficulty, a step-up switching power supply device having a power factor improving function or a method of obtaining a desired output by connecting a step-down switching power supply device in the subsequent stage is adopted.

  Therefore, as a critical operation type switching power supply device, an impedance circuit composed of a resistor, a capacitor, and a diode is incorporated in the current detection circuit, and the switching element is kept on even when the effective value of the AC input voltage is low. In addition, a switching power supply device that can increase the degree of design freedom and improve the derating of the switching element has been disclosed (see, for example, Patent Document 1).

JP 2004-350361 A

  However, according to the switching power supply device disclosed in Patent Document 1 described in the background art, when the auxiliary winding constituting the inductor is short-circuited due to substrate corrosion between the terminals of the auxiliary winding, the switching is performed depending on the resistance value of the short-circuited portion. Since the operation is continued, an excessive short-circuit current flows through the auxiliary winding, which raises the temperature of the auxiliary winding, and there is a risk of smoke or ignition.

  The present invention has been made to solve this problem, and restricts the generation of an excessive short circuit current when a short circuit between the terminals of the auxiliary winding constituting the inductor prevents the temperature of the auxiliary winding from rising. The purpose is to provide a power factor correction circuit with improved safety.

  To achieve the above object, a power factor correction circuit according to a first aspect of the present invention includes a full-wave rectifier circuit for rectifying and smoothing an AC power supply to generate a pulsating power supply, and a full-wave rectifier circuit. The primary side voltage dividing circuit for dividing the voltage level of the pulsating current power generated in this manner, the inductor having the main winding and the auxiliary winding connected to the full wave rectifier circuit, and switching driving the inductor, the full wave A transistor for storing the switching current in the main winding based on the pulsating current generated by the rectifier circuit, and voltage conversion using a voltage conversion resistor when the transistor is on when power is applied from the external power supply A first control circuit for switching the transistor to an off state and generating an electromotive force in the inductor so that the peak waveform of the switching current to be generated and the output waveform of the primary voltage dividing circuit are the same waveform; Main winding The induced voltage to al auxiliary winding is detected that the energy stored in the inductor based on emitted, and a second control circuit for switching the transistor from the off state to the on state. Between the auxiliary winding and the zero current detection circuit of the second control circuit, an excessive short-circuit current generated at the time of a short circuit due to substrate corrosion between the terminals of the auxiliary winding is limited, and the temperature of the auxiliary winding rises A protective resistor for preventing this is connected in series.

  The power factor correction circuit according to the second aspect of the present invention includes a diode bridge for rectifying an AC input voltage, an input capacitor for supplying a ripple current due to switching, and a main winding connected to the input capacitor. An inductor having a wire and an auxiliary winding, a transistor that performs switching to generate a counter electromotive voltage in the inductor, a diode that rectifies the voltage generated in the inductor by the switching operation of the transistor, and a voltage rectified by the diode. An output capacitor for smoothing and a protective resistor that is wound in series with the inductor to limit the short-circuit current and prevent a temperature rise of the auxiliary winding when the auxiliary winding is short-circuited and damaged Is.

  According to the power factor correction circuit of the present invention, since the protective resistor is wound in series in the auxiliary winding constituting the inductor, excessive power that occurs at the time of a short circuit due to substrate corrosion or the like between the terminals of the auxiliary winding. Short circuit current is limited, temperature rise of the auxiliary winding can be prevented, and safety can be enhanced by suppressing the risk of smoke and ignition.

FIG. 1 is a circuit block diagram showing a specific configuration of a power factor correction circuit according to an embodiment of the present invention.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments to which a power factor correction circuit of the invention is applied will be described with reference to the drawings.

  FIG. 1 is a circuit block diagram showing a specific configuration of a power factor correction circuit according to an embodiment of the present invention. The power factor correction circuit includes a load 1 such as an electric device, an AC power source 2, a full-wave rectifier circuit 3, a primary side voltage divider circuit 4, a boost type inductor 5, a transistor 6, a rectifying and smoothing circuit 7, and a secondary side. A voltage dividing circuit 8, an external power source 9, a control unit 10, a current limiting resistor R1, and a current / voltage converting resistor R2 are provided.

  Here, the full-wave rectifier circuit 3 is for rectifying and smoothing the AC power supply 1 to generate a pulsating power supply. The ripple current is generated by switching the diode bridge DB that rectifies the AC input voltage Vin and the inductor 5. And an input capacitor C1. In the diode bridge DB, the (+) side is connected to one end side of the main winding 50 constituting the inductor 5 and the (−) side is connected to a reference potential point. Further, in the input capacitor C1, the (+) side is connected between the (+) side of the diode bridge DB and one end side of the main winding 50, and the (−) side is connected to the reference potential point. .

  The primary side voltage dividing circuit 4 includes first and second voltage dividing resistors R10 and R11 connected in series in order to divide the voltage level of the pulsating power supply generated by the full-wave rectifier circuit 3. Yes. The first and second voltage dividing resistors R10 and R11 (connected in series) are connected in parallel between the (+) side and the (−) side of the diode bridge DB constituting the full-wave rectifier circuit 3. The input voltage detection circuit 100 constituting the control unit 10 is connected to the connection point.

  The inductor 5 has one end connected to the (+) side of the diode bridge DB constituting the full-wave rectifier circuit 3, an auxiliary winding 51 that receives the induced voltage of the main winding 50, And a protective resistor R3 wound in series with the inductor. The other end of the main winding 50 is connected to the anode of the diode D 1 that constitutes the rectifying and smoothing circuit 7. Further, one end side of the auxiliary winding 51 is connected to a reference potential point, and the other end side of the auxiliary winding 51 is a zero current detection circuit 101 constituting the control unit 10 via a protective resistor R3 and a current limiting resistor R1 sequentially. It is connected to the. Furthermore, the protective resistor R3 generates excessive short-circuit current when the auxiliary winding 51 is damaged due to corrosion of the substrate between the auxiliary winding 51 and the terminals P1 and P2 of the protective resistor. For example, the resistance having a resistance value of about 1 kΩ is suitable.

  The transistor 6 generates a back electromotive voltage in the inductor 5 to drive the inductor to switch the switching current (energy generated by the main winding 50 based on the pulsating current power generated in the full-wave rectifier circuit 3. It is for storage. According to the present embodiment, the transistor 6 is composed of a MOS type FET, and the gate of the FET is connected to a transistor driving circuit 102 constituting the control unit 10. The source of the FET is connected between the other end of the main winding 50 and the anode of the diode D1 constituting the rectifying / smoothing circuit 7. Further, the drain of the FET is connected to the reference potential point and the current detection circuit 103 constituting the control unit 10 via the current / voltage conversion resistor R2. Here, the voltage conversion resistor R2 is for converting a switching current flowing through the switching operation of the transistor 6 into a voltage.

  The rectifying / smoothing circuit 7 includes a diode D1 for rectifying the voltage generated in the inductor 5 by the switching operation of the transistor 6, and an output capacitor C2 for smoothing the voltage rectified by the diode D1. The cathode of the diode D1 is connected to one end of the load 1 whose other end is connected to the reference potential point. Further, in the output capacitor C2, the (+) side is connected between the cathode of the diode D1 and one end side of the load 1, and the (−) side is connected to a reference potential point.

  The secondary side voltage dividing circuit 8 divides the voltage smoothed by the output capacitor C1 constituting the rectifying and smoothing circuit 7 and generates the output voltage Vout to the load 1 in the third and fourth divisions connected in series. The resistors R12 and R13 are included. An output voltage detection circuit 104 constituting the control unit 10 is connected to a connection point of the third and fourth voltage dividing resistors R12 and R13 (connected in series).

  The external power source 9 is for supplying operating power to the control unit 10. As the external power supply 9, a power supply from an auxiliary winding included in a DC / DC converter (not shown) provided on the rear stage side of the power factor correction circuit or a dedicated small-capacity power supply is suitable.

  The control unit 10 includes the input voltage detection circuit 100, the zero current detection circuit 101, the transistor drive circuit 102, the current detection circuit 103, the output voltage detection circuit 104, and the control CPU 105 described above.

  In this control unit 10, the input voltage detection circuit 100 is for detecting the output waveform of the primary side voltage dividing circuit 4.

  The zero current detection circuit 101 indicates that the energy stored in the inductor 5 (due to the switching current) has been released, and outputs the output voltage of the auxiliary winding 51 connected through the current limiting resistor R1 and the protective resistor R3. It is intended to detect. Here, the current limiting resistor R1 is for limiting the input current to the zero current detection circuit 101, and may be provided in the circuit of the zero current detection circuit.

  The transistor drive circuit 102 is for controlling the switching operation to switch the transistor 6 between the on state and the off state and generating the back electromotive force in the inductor 5.

  The current detection circuit 103 detects the switching current based on the voltage converted via the voltage conversion resistor R2.

  The output voltage detection circuit 104 is for detecting the voltage level of the output voltage Vout from the secondary side voltage dividing circuit 8 to the load 1, and is controlled by the control CPU 105 so that the output voltage Vout becomes constant. .

  The control CPU 105 is for controlling each of the circuits 100 to 104 so that the input current from the AC power supply 2 becomes a sine wave similar to the input voltage and the output voltage Vout is constant.

  In the power factor correction circuit according to the embodiment of the present invention configured as described above, a specific operation in the current critical mode will be described below.

  When the AC input voltage Vin from the AC power source 2 shown in FIG. 1 is applied, the AC input voltage Vin is full-wave rectified by the diode bridge DB constituting the full-wave rectifier circuit 3. Here, since the capacitance of the input capacitor C1 is usually as small as 1 μF, a full-wave rectified voltage waveform is applied to both ends of the input capacitor C1.

  At this time, when operating power is supplied from the external power supply 9 to the control unit 10, the control CPU 105 controls the transistor drive circuit 102 to switch the transistor 6 from the off state to the on state. By this control, the main winding 50 constituting the inductor 5 is supplied with a voltage from the AC power supply 2 via the full-wave rectifier circuit 3, so that the current flowing through the inductor increases from “0” as time passes. Since the switching current flows through the path of the transistor 6 in the on state and the voltage conversion resistor R2, energy is stored in the inductor 5.

  Here, in order to improve the power factor in the current critical mode, it is necessary to make the input current from the AC power source 2 into a sine wave shape similar to the input voltage Vin, so the control CPU 105 of the control unit 10 has a current detection circuit 103. The waveform of the peak current of the switching current input to the inductor 5 and the full-wave rectified voltage waveform applied from the primary side voltage dividing circuit 4 to the input voltage detection circuit 100 flow through the inductor 5 so as to have the same waveform. When the current rises to a predetermined current value, the transistor drive circuit 102 is controlled to switch the transistor 6 from the on state to the off state.

  When the transistor 6 is switched to the OFF state as described above, a back electromotive force is generated in the inductor 5, and therefore, the input capacitor constituting the full-wave rectifier circuit 3 is connected to the terminal P 3 on the transistor 6 side in the main winding 50. A voltage higher than the voltage across C1 is generated, current flows from the inductor 5 through the path of the diode D1 and the output capacitor C2 constituting the rectifying and smoothing circuit 7, and the voltage is divided through the secondary side voltage dividing circuit 8. When the output voltage Vout is generated, the output voltage Vout is supplied to the load 1.

  Further, when the above-described power supply is performed, the switching current flowing through the inductor 5 decreases and becomes “0” as time elapses. Therefore, the zero current detection circuit 101 constituting the control unit 10 has the current limiting resistor R1. Based on the output voltage of the auxiliary winding 51 connected via the protective resistor R3, that is, the voltage level of the induced voltage from the main winding 50 to the auxiliary winding 51, the energy of the inductor 5 is released. Can be confirmed. Upon detecting this, the control CPU 105 continues the power supply to the load 1 by repeating the switching operation so far so as to control the transistor drive circuit 102 to switch the transistor 6 from the OFF state to the ON state. Can do.

  Next, when the auxiliary winding 51 constituting the inductor 5 is short-circuited between the terminals P1 and P2 due to substrate corrosion or the like and the auxiliary winding is damaged, the inductor 5 has a protective resistance R3. Since they are wound in series, an excessive short-circuit current does not flow, and the temperature increase of the auxiliary winding 51 can be prevented.

  The power factor correction circuit according to the present invention has been described with a specific embodiment. However, the present invention is not limited to this embodiment, and any system known so far can be used as long as the effect of the present invention is achieved. It goes without saying that even if there is, it can be adopted.

2 …… AC power supply 3 …… Full wave rectifier circuit DB …… Diode bridge C1 …… Input capacitor 4 …… Primary side voltage divider circuit 5 …… Inductor 50 …… Main winding 51 …… Auxiliary winding 6 …… Transistor 100... Input voltage detection circuit (first control circuit)
101 …… Zero current detection circuit (second control circuit)
102... Transistor drive circuit (first and second control circuits)
103 ... Current detection circuit (first control circuit)
105... Control CPU (first and second control circuits)
D1 …… Diode C2 …… Output capacitor R3 …… Protection resistance

Claims (2)

A full-wave rectifier circuit (3) for rectifying and smoothing the AC power supply (2) to generate a pulsating power supply;
A primary side voltage dividing circuit (4) for dividing a voltage level of the pulsating power supply generated by the full wave rectifier circuit;
An inductor (5) connected to the full-wave rectifier circuit and having a main winding (50) and an auxiliary winding (51);
A transistor (6) for switching driving the inductor and storing a switching current in the main winding based on the pulsating power source generated in the full-wave rectifier circuit;
When the transistor is in an ON state when power is supplied from an external power source (9), the peak waveform of the switching current converted through the voltage conversion resistor and the output waveform of the primary side voltage dividing circuit And a first control circuit (100, 102, 103, 105) for switching the transistor to an off state so as to have the same waveform and generating a back electromotive force in the inductor,
A second control circuit for detecting that energy stored in the inductor is released based on an induced voltage from the main winding to the auxiliary winding and switching the transistor from an off state to an on state ( 101, 102, 105)
Between the auxiliary winding and the zero current detection circuit (101) of the second control circuit, an excessive short-circuit current generated at the time of a short circuit due to substrate corrosion or the like between the terminals of the auxiliary winding is limited. A power factor correction circuit comprising a protective resistor (R3) connected in series for preventing temperature rise of the auxiliary winding.   A diode bridge (DB) for rectifying the AC input voltage (Vin), an input capacitor (C1) for supplying a ripple current by switching, a main winding (50) connected to the input capacitor, and an auxiliary winding An inductor (5) having a line (51), a transistor (6) that performs the switching to generate a back electromotive force in the inductor, and a voltage for rectifying a voltage generated in the inductor by the switching operation of the transistor. The diode (D1), the output capacitor (C2) for smoothing the voltage rectified by the diode, and the inductor wound in series, the short circuit current is limited when the auxiliary winding is short-circuited and damaged And a protective resistor (R3) for preventing a temperature rise of the auxiliary winding. Good circuit.

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