JP2011223819A - Power factor improving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power factor improving circuit which is capable of easily and automatically adjusting a target value of a boost voltage with high accuracy in accordance with an input voltage level.SOLUTION: The power factor improving circuit includes: a switching control circuit 28 for a boost chopper circuit 16; an input voltage detection circuit 44 for outputting an input voltage signal Vi; a reference pulse generator 46 for outputting a periodic reference pulse V46 of which the duty ratio is determined in accordance with the input voltage signal Vi; an averaging circuit 48 for outputting an averaged voltage V48 of the reference pulse V46; and a correction signal injection resistance 50 for injecting a target value correction signal Ib corresponding to the averaged voltage V48 into a boost voltage signal Vo1 or a reference voltage V34. A target value Va of a boost voltage Vo is corrected by the target value correction signal Ib so that the boost voltage Vo is higher than a peak value Vsp of a rectified voltage Vs. The target value Va is corrected so that the higher the input voltage Vi becomes, the higher the boost voltage Vo becomes.

Description

  The present invention relates to a power factor correction circuit that includes a step-up chopper circuit, shapes a waveform of an input current supplied from a commercial power supply, and outputs a predetermined DC voltage.

  Conventionally, for example, a power factor correction circuit having a wide input voltage range that can handle commercial voltages (AC100V system, 240V system, etc.) that are compatible with all over the world is a boost chopper circuit even when used in a region where the input voltage is high. In general, the target value of the boosted voltage is fixed to a value higher than the peak value of the maximum input voltage so that the main switching element is turned on / off to perform the power factor correction operation. For this reason, when used in a region where the input voltage is low, the boosted voltage becomes very high compared to the input voltage, and the load on the load connected to the subsequent stage increases. For example, when the subsequent load is a DC-DC converter, the outer shape becomes large in order to improve internal insulation, or high voltage components with high conduction resistance must be selected as the main switching element, resulting in a reduction in efficiency. The problem of doing was occurring.

  In recent years, in order to solve this problem, there have been proposed a plurality of circuit technologies for automatically adjusting the boosted voltage to be lower when the input voltage is low and to increase the boosted voltage when the input voltage is high. For example, as disclosed in Patent Document 1, the boost voltage matches the target value by driving the main switching element on and off so that the error between the boost voltage output from the boost chopper circuit and the reference voltage is reduced. And the second control means for controlling so that when the input voltage becomes higher and its peak value approaches the target value of the boost voltage, the reference voltage is varied, and the target value of the boost voltage is higher than the peak value of the input voltage. There is a power supply device including a reference voltage variable circuit that automatically corrects a high value. As an embodiment of the reference voltage variable circuit, the pulsating voltage output from the rectifier circuit is peak-held by a diode and a capacitor to detect the peak value, the peak hold voltage is resistance-divided, and the divided voltage is supplied to a constant voltage source. A circuit that outputs a higher voltage as a reference voltage is described. According to this power supply device, the power factor correction operation can be performed in the entire range of the input voltage, and when used in a region where the input voltage is low, the boost voltage is set to a correspondingly low voltage. Therefore, the load of the load connected to the subsequent stage is reduced.

JP-A-3-78469

  However, the power supply device of Patent Document 1 needs to change the constants of the voltage dividing resistor and many other components of the reference voltage variable circuit when changing the specification of the input voltage range. Changes and re-evaluations are required, and production is complicated in terms of mass production member management. Even in the case of the same power supply device, the target voltage of the boost voltage relative to the input voltage may vary depending on the characteristics of each component constituting the reference voltage variable circuit, the boost voltage detection circuit, the input voltage detection circuit, etc. There was a problem that the setting varied greatly and the performance of the assembled product was not stable.

  The present invention has been made in view of the above-described background art, and an object thereof is to provide a power factor correction circuit capable of automatically and accurately adjusting a target value of a boosted voltage according to the level of an input voltage. And

The present invention includes a rectifying circuit that rectifies an AC input voltage and outputs a pulsating rectified voltage, a choke coil, a main switching element, a rectifying element, and a smoothing capacitor, and the boosted voltage obtained by boosting the rectified voltage A boost chopper circuit that is generated at both ends of the smoothing capacitor and supplies power to the load; a boost voltage signal corresponding to the boost voltage; and a target value of the boost voltage by amplifying a difference between the reference voltage and the boost voltage signal Power factor improvement provided with an error amplifier that determines the error, and a switching control unit that receives an error amplification signal output from the error amplifier and controls on / off of the main switching element so that the boosted voltage becomes the target value A circuit,
An input voltage detection circuit that detects the input voltage and outputs an input voltage signal, and outputs a reference pulse that is a rectangular wave with a fixed period and has a high-level and low-level time ratio determined according to the input voltage signal A reference pulse generator, an averaging circuit that outputs an averaged voltage of the reference pulse, a correction signal injection circuit that injects a target value correction signal corresponding to the averaged voltage into the boosted voltage signal or the reference voltage, The target value correction unit configured with
The target value correction signal output from the target value correction unit corrects the target value of the boosted voltage so that the boosted voltage becomes higher than the peak value of the rectified voltage regardless of the level of the input voltage. In addition, the target value of the boosted voltage is corrected so that the boosted voltage is relatively low when the input voltage is low and the boosted voltage is relatively high when the input voltage is high. It is an improvement circuit.

  Further, the target value correction unit outputs the target value correction signal that makes the target value of the boost voltage constant within a range where the input voltage is equal to or lower than a predetermined voltage.

  The reference pulse generator may be provided in a microcomputer, and the relationship between the reference pulse duty ratio and the input voltage signal may be changed by rewriting a program.

  In addition, an overvoltage protection circuit that stops the on / off operation of the main switching element when the boosted voltage exceeds an overvoltage reference value, the error amplifier includes the boosted voltage regardless of the presence or absence of the target value correction signal. The target value is determined to be equal to or less than the overvoltage reference value.

  In addition, a series circuit of a diode and an inrush current limiting resistor for supplying a current from the output of the rectifier circuit to the smoothing capacitor when an input voltage is applied is provided.

  Since the power factor correction circuit according to the present invention includes a target value correction unit including the input voltage detection circuit, the reference pulse generation circuit, the averaging circuit, and the correction signal injection circuit as described above, the specification of the input voltage range is provided. Even when designing products with different values, the relationship between the input voltage and the boost voltage target value can be adjusted simply by changing the circuit constants of the input voltage detection circuit. The number can be kept to a minimum. Furthermore, if the reference pulse generation circuit is provided in the microcomputer so that the relationship between the reference pulse duty ratio and the input voltage signal can be changed by rewriting the program, it is necessary to change the constant of the input voltage detection circuit. Absent.

  In addition, if the reference pulse generation circuit is configured in the microcomputer as described above, for example, when mass-producing a product equipped with this power factor correction circuit, an energization test is performed in the shipping inspection process, and the time ratio of the reference pulse is determined. The program part that defines the relationship between the input voltage and the input voltage signal is rewritten to match the characteristics of each product, and finely adjusted so that the relationship between the input voltage and the boost voltage is within the standard range. Variations can be easily corrected, product accuracy can be improved, and productivity is greatly improved. Further, the number of points of the reference pulse generation circuit itself can be greatly reduced.

It is a block diagram which shows the power factor improvement circuit of 1st embodiment of this invention. It is a circuit diagram which shows the specific structure of the power factor improvement circuit of 1st embodiment. It is a graph explaining operation | movement of the power factor improvement circuit of 1st embodiment. It is a circuit diagram which shows the specific structure of the power factor improvement circuit of 2nd embodiment of this invention. It is a graph explaining operation | movement of the power factor improvement circuit of 2nd embodiment.

  Hereinafter, a first embodiment of a power factor correction circuit according to the present invention will be described with reference to FIGS. As shown in the block diagram of FIG. 1, the power factor correction circuit 10 of this embodiment is connected to a commercial power supply 12 at an input terminal 14a and outputs a rectified voltage Vs obtained by full-wave rectification of an AC input voltage Vi. 14 is provided. A boost chopper circuit 16 that outputs a boosted voltage Vo by intermittently rectifying and smoothing the rectified voltage Vs is connected to the output stage of the rectifier circuit 14. A load 18, which is a general electronic device, a DC-DC converter, or the like, is connected to the output terminal 16 a of the boost chopper circuit 16 to supply the boost voltage Vo.

  The step-up chopper circuit 16 includes a choke coil 20 having one end connected to the output of the rectifier circuit 14, a main switching element 22 connected between the other end of the choke coil 20 and the ground, and both ends of the main switching element 22. Are composed of a rectifier diode 24 that rectifies the intermittent voltage generated at, and a smoothing capacitor 26 that smoothes the output of the rectifier diode 24 and generates a DC boosted voltage Vo.

  On / off of the main switching element 22 is controlled by a switching control circuit 28. The switching control circuit 28 shapes the waveform of the input current supplied from the commercial power source to improve the power factor, and also turns on and off the main switching element 16 so that the boosted voltage Vo becomes a predetermined target value Va. To decide.

  A control system that stabilizes the boosted voltage Vo includes a boosted voltage detection circuit 30, an error amplifier 32, a reference voltage source 34, a target value correction unit 36, and a switching control circuit 28. The boosted voltage detection circuit 30 detects the boosted voltage Vo and outputs a boosted voltage signal Vo1. The error amplifier 32 receives the boosted voltage signal Vo1 and determines the target value Va of the boosted voltage Vo by amplifying the difference between the reference voltage V34 of the reference voltage source 34 and the boosted voltage signal Vo1. The target value correction unit 36 detects the peak value Vsp of the rectified voltage Vs and outputs a target value correction signal Ib corresponding to the detected peak value Vsp. The target value correction signal Ib is injected into the boosted voltage detection circuit 30, thereby changing the boosted voltage signal Vo1 and correcting the target value Va. The switching control circuit 28 receives the output of the error-up 34 and controls the main switching element 16 on and off so that the boosted voltage Vo matches the corrected target value Va.

  Further, the power factor correction circuit 10 sends a signal to the switching control circuit 28 to turn on the main switching element 16 when the boosted voltage Vo exceeds the overvoltage reference value V38 that is a voltage value higher than the target value Va for some reason. An overvoltage protection circuit 38 that stops off and prevents the application of an excessive voltage to the load 18 is provided. Furthermore, a series circuit of a diode 40 and an inrush current limiting resistor 42 that flow current from the output of the rectifier circuit 14 toward the smoothing capacitor 26 when the input voltage Vi is input is provided.

  Next, specific configurations of the boost voltage detection circuit 30, the target value correction unit 36, the error amplifier 32, and the reference voltage source 34 will be described based on the circuit diagram of FIG. The boosted voltage detection circuit 30 is a series circuit of resistors 30a, 30b, and 30c connected in parallel to both ends of the smoothing capacitor 26 that generates the boosted voltage Vo, and the total value of the voltages generated in the ground-side resistors 30b and 30c is calculated. The boosted voltage signal Vo1 is output.

  The target value correction unit 36 includes an input voltage detection circuit 44, a reference pulse generator 46, an averaging circuit 48, and a correction signal injection resistor 50 that is a correction signal injection circuit. The input voltage detection circuit 44 detects the rectified voltage Vs in which the levels of the input voltage Vi appear equally, and outputs an input voltage signal Vi1 corresponding to the level of the peak value Vsp.

  The reference pulse generator 46 outputs a reference pulse V46, which is a rectangular wave with a fixed period and has a high-level and low-level time ratio determined according to the input voltage signal Vi1. Here, the reference pulse generator 46 is provided in the microcomputer, and the relationship between the duty ratio of the reference pulse V46 and the input voltage signal Vi1 is defined by the program, and when the definition is changed, the program is rewritten. This can be done freely. The relationship between the duty ratio D of the reference pulse V46 and the input voltage signal Vi1 will be described in detail later in the description of the operation.

  The averaging circuit 48 includes resistors 48a and 48b that divide the reference pulse V46, and a capacitor 48c connected in parallel to the ground-side resistor 48b. An averaged voltage V48 is output.

The correction signal injection resistor 50 is connected between the output of the averaging circuit 48 and the midpoints of the resistors 30b and 30c of the boosted voltage detection circuit 30. Here, the resistance value of the correction signal injection resistor 50 is set to a resistance value sufficiently larger than the resistance value of the resistor 30c, and the resistance value of the resistance value 30c is such that the voltage generated at both ends thereof is higher than the average voltage V48. It is set to be low. Therefore, the target value correction signal Ib, which is a current signal injected into the boosted voltage detection circuit 30 via the correction signal injection resistor 50, can be expressed as in equation (1).

ここで、Ｒ３０ｃは、抵抗３０ｃの抵抗値である。 Here, R50 is the resistance value of the correction signal injection resistor 50. When the target value correction signal Ib flows through the resistor 30c, the boosted voltage signal Vo1 changes, and the amount of change ΔVo1 can be expressed as in equation (2).

Here, R30c is the resistance value of the resistor 30c.

  The error amplifier 32 is an inverting amplifier circuit that receives the reference voltage signal Vo1 at the inverting input terminal and the reference voltage V34 at the non-inverting input terminal, and amplifies and outputs the difference. When the reference voltage signal Vo1 and the reference voltage V34 are equal, the error amplifier 32 outputs a constant voltage, and the switching control circuit 28 receiving the voltage determines that the boosted voltage Vo is equal to the target value Va, The on-time ratio of the main switching element 22 is continued as it is. When the reference voltage signal Vo1 becomes higher than the reference voltage V34, the output of the error amplifier 32 decreases, and the switching control circuit 28 receiving it determines that the boosted voltage Vo is higher than the target value Va. Control is performed such that the boosted voltage Vo is lowered by decreasing the ON-time ratio of the switching element 22. On the contrary, when the reference voltage signal Vo1 becomes lower than the reference voltage V34, the output of the error amplifier 32 rises, and the switching control circuit 28 receiving it determines that the boosted voltage Vo is lower than the target value Va. Then, the boosting voltage Vo is controlled to be increased by increasing the on-time ratio of the main switching element 22.

  When the target value correction signal Ib changes, the target value Va is corrected to a new target value Va. For example, when the target value correction signal Ib decreases while the boosted voltage Vo is equal to the target value Va, the boosted voltage signal Vo1 decreases based on the equation (2), and the reference voltage signal Vo1 is higher than the reference voltage V34. Therefore, the output of the error amplifier 32 rises, and the switching control circuit 28 receiving it determines that the boosted voltage Vo is lower than the target value Va, and increases the on-time ratio of the main switching element 22. Control is performed so that the boosted voltage Vo increases. That is, if the target value correction signal Ib decreases, the target value Va is corrected in the direction of increasing the boosted voltage Vo. Conversely, if the target value correction signal Ib increases, the target value Va becomes the boosted voltage. The correction is made in the direction of lowering Vo.

  The error amplifier 32 and the reference voltage 34 are set so that the upper limit value of the target value Va is equal to or lower than the overvoltage reference value Vovp regardless of the presence or absence of the target value correction signal Ib that is the output of the target value correction unit 36. Yes.

  Next, the operation of the power factor correction circuit 10 will be described with reference to FIG. In the reference pulse generator 46, as described above, the relationship between the duty ratio D of the reference pulse V46 and the input voltage signal Vi1 is defined by a program. Specifically, as shown in FIG. 3, when the input voltage Vi is less than or equal to Vk, the time ratio D does not change and is a constant value, and when the input voltage Vi exceeds Vk, the time ratio D gradually decreases. Is defined as Therefore, the average voltage V48 does not change in the range where the input voltage Vi is equal to or lower than the voltage Vk, the target value Va of the boosted voltage Vo shows a constant value, and when the input voltage Vi exceeds Vk, the average voltage V48 gradually increases. The target value Va gradually increases. At this time, the target value Va is set so as to be always higher than the peak value Vsp of the rectified voltage Vs. Therefore, the boost chopper circuit 16 has the main switching element 22 turned on / off in the entire range of the input voltage Vi. It can be turned off to improve the power factor.

  As described above, the power factor correction circuit 10 rewrites the program of the reference pulse generation circuit 36 provided in the microcomputer to design the input voltage Vi and the target value, for example, when designing one having different input voltage range specifications. Since it is only necessary to appropriately change the relationship with Va (boost voltage Vo), design and evaluation are easy, and the number of parts to be changed can be minimized.

  In addition, when mass-producing a product having the power factor correction circuit 10 mounted thereon, a program part that performs an energization test in the shipping inspection process and defines the relationship between the time ratio D of the reference pulse V46 and the input voltage signal Vi1 can be assembled. If the product is rewritten according to the characteristics of each product and finely adjusted so that the relationship between the boosted voltage Vo and the input voltage Vi falls within the standard range, variations in individual products can be easily corrected, and product accuracy can be improved. It can be increased and mass productivity is also improved. Also, the number of parts of the reference pulse generation circuit can be greatly reduced.

  Further, when the input voltage Vi is used in the range of Vk or less, the target value Va is fixed to a predetermined value and a boost voltage Vo of a certain level or more is ensured. Therefore, after the input voltage Vi is cut off, the boost voltage Vo It is possible to secure a certain holding time until the value decreases.

  Further, an overvoltage protection circuit 38 for stopping the operation of the boost chopper circuit 16 when the boosted voltage Vo reaches the overvoltage reference value Vovp is provided, and the error amplifier 32 and the reference voltage 34 are output from the target value correction unit 36. Regardless of the presence or absence of the target value correction signal Ib, the upper limit value of the target value Va is configured to be equal to or less than the overvoltage reference value Vovp. Accordingly, when the boosted voltage Vo increases in a specific failure mode, double protection against overvoltage is provided, so that the reliability and safety of the product are further improved. Further, as described above, when the relationship between the boost voltage Vo and the input voltage Vi is finely adjusted in the energization test, even if the characteristics of the parts constituting the control system of the boost voltage vary most, the overvoltage at the stage before the fine adjustment Since the protection circuit 38 does not work, fine adjustment work can be performed without any trouble.

  In addition, when an inrush current prevention circuit composed of a series circuit of a diode 40 and an inrush current limiting resistor 42 that flows current from the output of the rectifier circuit 14 toward the smoothing capacitor 26 when the input voltage Vi is applied, the boosted voltage is added. Since the target value Va of Vo is always higher than the peak value Vsp of the rectified voltage Vs, no current flows through the diode 40 and the inrush current limiting resistor 42 during steady operation, and no loss occurs in this series circuit. Therefore, measures such as the use of the high-power diode 40 and the inrush current limiting resistor 42 and the provision of a short-circuit switch for short-circuiting both ends of the inrush current limiting resistor 42 become unnecessary. Can be made compact and inexpensive.

  As described above, in the power factor correction circuit 10, the correction signal injection resistor 50 is set to a resistance value sufficiently larger than the resistance 30c, and the resistance value of the resistance value 30c is equal to the voltage generated at both ends thereof. It is set to be lower than the activation voltage V48. Therefore, the target value correction signal Ib defined by the expression (1) can be generated only in the direction of flowing into the resistor 30c. However, the target value correction signal Ib can be generated in both directions by changing the magnitude relation between the resistance values of the correction signal injection resistor 50 and the resistor 30c. Then, by changing the time ratio of the reference pulse V46 and raising or lowering the average voltage V48, not only the operation of raising the boost voltage Vo1, but also the operation of lowering it can be performed freely.

  Next, a second embodiment of the power factor correction circuit according to the present invention will be described with reference to FIGS. Here, the same components as those of the power factor correction circuit 10 of the first embodiment are denoted by the same reference numerals and description thereof is omitted. In the power factor improvement circuit 60 of the second embodiment, compared to the configuration of the power factor improvement circuit 10, the overvoltage protection circuit 38 is deleted, the series circuit of the diode 40 and the inrush current limiting resistor 42 is deleted, and further, the target A difference is that a target value control unit 62 is provided instead of the value correction unit 36.

  Here, the load 18a to which the power factor correction circuit 60 supplies the boosted voltage Vo includes a safety device for preventing its own damage when an excessive voltage is input. There is no need to provide an overvoltage circuit 38 for load protection. Further, the power factor correction circuit 60 has a relatively small capacitance of the smoothing capacitor 26, and the energy of the rush current when the input is turned on is small. Therefore, if the resistance component existing in the winding of the choke coil 20 is used, the rush current is increased. Can be easily suppressed. Therefore, in the power factor correction circuit 60, the series circuit of the inrush current limiting resistor 42 and the diode 40 is omitted.

  Hereinafter, the configuration of the control system for the boosted voltage Vo will be described in detail with a focus on a target value correction unit 62 provided instead of the target value correction unit 36. The control system that stabilizes the boosted voltage Vo includes a boosted voltage detection circuit 30, a target value correction unit 62, an error amplifier 32, and a reference voltage source 34.

  The boosted voltage detection circuit 30 is configured by a series circuit of resistors 30a, 30b, and 30c connected in parallel to both ends of the smoothing capacitor 26 that generates the boosted voltage Vo, and the total value of the voltages generated in the ground-side resistors 30b and 30c. Is output as the boosted voltage signal Vo1. Either one of the resistors 30b and 30c may be omitted, but here two resistors are provided in series for the purpose of finely adjusting the voltage division ratio with the resistor 30a.

  The target value correction unit 62 includes an input voltage detection circuit 44, a reference pulse generator 54, an averaging circuit 48, and a correction signal injection buffer 66 that is a correction signal injection circuit. That is, as compared with the configuration of the target value correction unit 36 described above, a reference pulse generator 64 and a correction signal injection buffer 66 are provided instead of the reference pulse generator 46 and the correction signal injection resistor 50.

  The input voltage detection circuit 44 detects the rectified voltage Vs in which the levels of the input voltage Vi appear equally, and outputs an input voltage signal Vi1 corresponding to the level of the peak value Vsp.

  The reference pulse generator 64 outputs a reference pulse V64 which is a rectangular wave having a fixed period and whose time ratio D between high level and low level is determined according to the input voltage signal Vi1. Similar to the reference pulse generator 46, the reference pulse generator 64 is provided in the microcomputer, and the relationship between the time ratio D of the reference pulse V64 and the input voltage signal Vi1 is defined by a program, and the relationship is changed. When doing this, it can be done freely by rewriting the program. The relationship between the duty ratio D of the reference pulse V64 and the input voltage signal Vi1 will be described later in the description of the operation.

  The averaging circuit 48 includes resistors 48a and 48b that divide the reference pulse V46, and a capacitor 48c connected in parallel to the ground-side resistor 48b. A DC pulse obtained by averaging the reference pulse V64 at both ends of the capacitor 48c. An averaged voltage V48 is output.

The correction signal injection buffer 66 receives the averaged voltage V48 output from the averaging circuit 48 at a high impedance, and outputs it at a low impedance between the negative output terminal of the reference voltage source 34 and the ground. Here, since the amplification factor of the correction signal injection buffer 66 is 1, the target value correction signal Vb injected into the reference voltage source 34 is equal to the average voltage V48. When this target value correction signal Vb is generated, a reference voltage V34, which is one terminal voltage of an error amplifier 32 to be described later, changes, and the amount of change ΔV34 can be expressed as in equation (3).

  The error amplifier 32 is an inverting amplifier circuit that receives the reference voltage signal Vo1 at the inverting input terminal and the reference voltage V34 at the non-inverting input terminal, and amplifies and outputs the difference. When the reference voltage signal Vo1 and the reference voltage V34 are equal, the error amplifier 32 outputs a constant voltage, and the switching control circuit 28 receiving the voltage determines that the boosted voltage Vo is equal to the target value Va, The on-time ratio of the main switching element 22 is continued. When the reference voltage V34 becomes lower than the reference voltage signal Vo1, the output of the error amplifier 32 decreases, and the switching control circuit 28 receiving it determines that the boosted voltage Vo is higher than the target value Va. Control is performed such that the boosted voltage Vo is lowered by decreasing the ON-time ratio of the switching element 22. On the other hand, when the reference voltage V34 becomes higher than the reference voltage signal Vo1, the output of the error amplifier 32 increases, and the switching control circuit 28 receiving it determines that the boosted voltage Vo is lower than the target value Va. Then, the boosting voltage Vo is controlled to be increased by increasing the on-time ratio of the main switching element 22.

  When the target value correction signal Vb changes, the target value Va is corrected to a new target value Va. For example, when the target value correction signal Vb increases while the boosted voltage Vo is equal to the target value Va, the reference voltage V34 increases based on the equation (3), and the reference voltage V34 is higher than the reference voltage signal Vo1. Therefore, the output of the error amplifier 32 rises, and the switching control circuit 28 receiving it determines that the boosted voltage Vo is lower than the target value Va, and increases the on-time ratio of the main switching element 22 to boost the voltage. The voltage Vo is controlled to be high. That is, if the target value correction signal Vb increases, the target value Va is corrected in the direction of increasing the boosted voltage Vo. Conversely, if the target value correction signal Vb decreases, the target value Va becomes the boosted voltage. The correction is made in the direction of lowering Vo.

  Next, the operation of the power factor correction circuit 60 will be described with reference to FIG. In the reference pulse generator 64, as described above, the relationship between the duty ratio D of the reference pulse V64 and the input voltage signal Vi1 is defined by a program. Specifically, as shown in FIG. 5, when the input voltage Vi is less than or equal to Vk, the time ratio D does not change and is a constant value, and when the input voltage Vi exceeds the voltage Vk, the time ratio D gradually increases. It is defined to be Therefore, the average voltage V48 does not change when the input voltage Vi is less than or equal to Vk, the target value Va of the boost voltage Vo shows a constant value, and when the input voltage Vi exceeds Vk, the average voltage V48 gradually increases. The target value Va gradually increases. At this time, the target value Va is set so as to be always higher than the peak value Vsp of the rectified voltage Vs. Therefore, the boost chopper circuit 16 has the main switching element 22 turned on / off in the entire range of the input voltage Vi. It can be turned off to improve the power factor.

  As described above, the power factor correction circuit 60 has the target value correction unit 62 different from that of the power factor correction circuit 10, but can obtain substantially the same operational effects.

  Note that the power factor correction circuit of the present invention is not limited to the above embodiment. For example, the input voltage detection circuit can also be used as the input voltage detection circuit that the switching control circuit has for power factor improvement. Further, if the level of the input voltage Vi can be detected with high accuracy, instead of the method of observing the rectified voltage output from the rectifier circuit, the AC voltage at the previous stage of the rectifier circuit, the voltage across the choke coil of the boost chopper circuit, etc. The method of observing

  In addition, the reference pulse generator may be configured by combining a plurality of discrete components instead of the microcomputer as long as the operation of converting the input voltage signal into the time ratio of the reference pulse can be performed with high accuracy. Also good. In addition, the relationship between the input voltage signal and the time ratio of the reference pulse does not need to be strictly a linear relationship, and in consideration of the area where the power factor correction circuit is installed and the usage conditions, a curved relationship or staircase It may be defined in a state relationship.

  Further, the correction signal injection circuit can freely select a circuit means that can easily inject the target value correction signal in accordance with the configuration of the boost voltage detection circuit and the reference voltage source.

DESCRIPTION OF SYMBOLS 10,60 Power factor improvement circuit 14 Rectifier circuit 16 Boost chopper circuit 22 Main switching element 28 Switching control circuit 30 Boost voltage detection circuit 32 Error amplifier 34 Reference voltage source 36, 62 Target value correction | amendment part 38 Overvoltage protection circuit 40 Diode 42 Inrush current Limiting resistor 44 Input voltage detection circuit 46, 64 Reference pulse generator 48 Averaging circuit 50 Correction signal injection resistor 66 Correction signal injection buffer D Time ratio Ib, Vb Target value correction signal Va Target value of boosted voltage Vi Input voltage Vi1 Input voltage Signal Vo Boost Voltage Vo1 Boost Voltage Signal Vs Rectified Voltage V34 Reference Voltage V48 Averaged Voltage V46, V64 Reference Pulse

Claims (5)

A rectifier circuit that rectifies an AC input voltage and outputs a pulsating rectified voltage;
A boosting chopper circuit having a choke coil, a main switching element, a rectifying element and a smoothing capacitor, generating a boosted voltage obtained by boosting the rectified voltage at both ends of the smoothing capacitor, and supplying power to a load;
An error amplifier which receives a boosted voltage signal corresponding to the boosted voltage and determines a target value of the boosted voltage by amplifying a difference between a reference voltage and the boosted voltage signal;
In a power factor correction circuit comprising a switching control unit which receives an error amplification signal output from the error amplifier and controls on / off of the main switching element so that the boosted voltage becomes the target value.
An input voltage detection circuit for detecting the input voltage and outputting an input voltage signal;
A reference pulse generator that outputs a reference pulse that is a rectangular wave having a constant period and has a high-level and low-level time ratio determined according to the input voltage signal;
An averaging circuit that outputs an averaged voltage of the reference pulse;
A target value correction unit configured with a correction signal injection circuit that injects a target value correction signal corresponding to the averaged voltage into the boosted voltage signal or the reference voltage;
By the target value correction signal output by the target value correction unit,
Regardless of the level of the input voltage, the target value of the boosted voltage is corrected so that the boosted voltage is higher than the peak value of the rectified voltage, and
The target value of the boosted voltage is corrected so that the boosted voltage is relatively low when the input voltage is low, and the boosted voltage is relatively high when the input voltage is high. Power factor correction circuit to do.   2. The power factor correction circuit according to claim 1, wherein the target value correction unit outputs the target value correction signal that makes a target value of the boost voltage constant in a range where the input voltage is equal to or lower than a predetermined voltage.   3. The power factor correction circuit according to claim 1, wherein the reference pulse generator is provided in a microcomputer, and the relationship between the duty ratio of the reference pulse and the input voltage signal can be changed by rewriting a program. An overvoltage protection circuit that stops the on / off operation of the main switching element when the boosted voltage exceeds an overvoltage reference value;
4. The power factor correction circuit according to claim 1, wherein the error amplifier determines the target value so that the boosted voltage is equal to or lower than the overvoltage reference value regardless of the presence or absence of the target value correction signal. 5. 4. The power factor correction circuit according to claim 1, further comprising: a series circuit of a diode and an inrush current limiting resistor that allow current to flow from the output of the rectifier circuit toward the smoothing capacitor when an input voltage is applied. 5.

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