A circuit and method for improving power factor of power supply

Abstract

The present invention discloses a circuit and method for improving the power factor of a power supply. The circuit includes an AC input terminal ACIN, a rectifier and filter circuit, a PFC circuit, and a boost switching power supply main circuit. The boost switching power supply main circuit includes a switching power supply chip and its peripheral circuits. The input end of the AC input terminal ACIN is connected to an external AC power supply; the input end of the rectifier and filter circuit is connected to the output end of the AC input terminal ACIN; the input end of the PFC circuit is connected to the output end of the rectifier and filter circuit, and the other end is grounded; the output end of the PFC circuit is connected to the voltage feedback input pin of the switching power supply chip, and the switching power supply chip U1 is connected to its peripheral circuits. The present invention superimposes a waveform in phase with the rectified AC input voltage on the output DC voltage VDD, so that the AC input current changes with the AC input voltage, thereby improving the power factor of the power supply.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply, and in particular to a circuit and method for improving the power factor of a power supply. Background Art

[0002] Among AC circuit parameters, the cosine of the phase difference between voltage and current is called power factor. Numerically, power factor is the ratio of active power P to apparent power S, i.e., cos φ = P / S. The magnitude of the power factor depends on the nature of the circuit's load. For example, if the circuit contains only resistive loads such as incandescent bulbs and resistance furnaces, the power factor is 1. If the circuit also contains inductive or capacitive loads, the power factor is less than 1. If the circuit contains only inductive or capacitive loads, the power factor is 0. Power factor is an important technical metric for measuring the efficiency of electrical equipment. A low power factor indicates that the circuit uses a large amount of reactive power to convert the alternating magnetic field, which reduces equipment utilization and increases line power losses.

[0003] Existing switching power supplies typically include a PFC (Power Factor Correction) circuit. Common active PFC circuits typically include a main PFC circuit and related control circuitry, enabling the input current to effectively track changes in the input voltage, thereby ensuring that the switching power supply's power factor and total harmonics meet requirements. However, in switching power supplies, the PFC circuit also includes a filter capacitor in the upstream stage. When the AC voltage input from the power grid is within a zero-crossing period, the presence of the filter capacitor causes the downstream voltage of the rectifier bridge to be higher than the input voltage of the rectifier bridge, resulting in no current flowing through the rectifier bridge during this period. As a result, the input current of the rectifier bridge cannot track changes in the input voltage, which in turn leads to a low power factor of the switching power supply. Summary of the Invention

[0004] The object of the present invention is to overcome the deficiencies in the prior art and provide a circuit and method for improving the power factor of a power supply, so as to improve the power factor of the power supply.

[0005] The purpose of the present invention is achieved through the following two technical solutions:

[0006] In a first aspect, the present invention provides a circuit for improving the power factor of a power supply, comprising:

[0007] AC input terminal ACIN: the AC input terminal ACIN is connected to an external AC power source;

[0008] Rectifier and filter circuit: The input end of the rectifier and filter circuit is connected to the AC input terminal ACIN, and the rectifier and filter circuit is used to convert the input AC voltage into a pulsating low-frequency DC voltage;

[0009] a PFC circuit, wherein an input end of the PFC circuit is connected to an output end of the rectifier and filter circuit, and the PFC circuit constitutes an inverting amplifier circuit for inverting and amplifying an AC component in the pulsating low-frequency DC voltage output by the rectifier and filter circuit;

[0010] Boost switching power supply main circuit: The Boost switching power supply main circuit includes a switching power supply chip U1 and a peripheral circuit. The voltage feedback input pin of the switching power supply chip U1 is connected to the output end of the PFC circuit. The switching power supply chip U1 is connected to the peripheral circuit. The input end of the peripheral circuit is connected to the output end of the rectifier and filter circuit. The Boost switching power supply main circuit outputs the VDD power supply.

[0011] Furthermore, the rectifier and filter circuit includes a diode D1, a diode D2, a diode D3, a diode D4, and a capacitor C1. The diode D1, the diode D2, the diode D3, and the diode D4 constitute a rectifier bridge. The input end of the rectifier bridge is connected to the AC input terminal ACIN, the first output end of the rectifier bridge is connected to one end of the capacitor C1, and the common end is connected to the PFC circuit and the Boost boost switching power supply main circuit. The second output end of the rectifier bridge is grounded, and the other end of the capacitor C1 is grounded.

[0012] Furthermore, the PFC circuit includes a capacitor C2, a capacitor C4, a capacitor C12, a resistor R1, a resistor R2, a resistor R4, a resistor R9, a controllable precision voltage regulator U3, and a power supply VDD, one end of the capacitor C2 is connected to the output end of the rectifier and filter circuit, the other end of the capacitor C2 is connected to one end of the resistor R4, the other end of the resistor R4 is connected to one end of the resistor R2, and the common end is connected to one end of the resistor R5, one end of the capacitor C12, and the control end of the controllable precision voltage regulator U3, one end of the resistor R5 is connected to the input end of the controllable precision voltage regulator U3, and the common end is grounded, the other end of the resistor R2 is connected to one end of the resistor R1, and the common end is connected to the other end of the capacitor C12, the output end of the controllable precision voltage regulator U3, and one end of the capacitor C4, the other end of the resistor R1 is connected to the power supply VDD, the other end of the capacitor C4 is connected to one end of the resistor R9, and the other end of R9 is connected to the main circuit end of the Boost switching power supply.

[0013] Furthermore, the gain of the PFC circuit is A=R2 / R4.

[0014] Furthermore, the controllable precision voltage regulator U3 is specifically TL431.

[0015] Furthermore, a voltage at a connection terminal between the capacitor C2 and the resistor R4 is the same as the AC input voltage.

[0016] Furthermore, the main circuit end of the Boost boost switching power supply includes a switching power supply chip U1, a MOS tube Q2, a diode D7, an inductor L3, a resistor R3, a resistor R6, a resistor R7, a resistor R8, a capacitor C3, a capacitor C5, a capacitor C7, a capacitor C10 and a VDD power output terminal. The first pin of the switching power supply chip U1 is grounded, the third pin of the switching power supply chip U1 is connected to one end of the capacitor C10, the fourth pin of the switching power supply chip U1 is connected to the output end of the PFC circuit and the common end is connected to one end of the resistor R7 and one end of the resistor R8, the fifth pin of the switching power supply chip U1 is connected to the gate of the MOS tube Q2, the sixth pin of the switching power supply chip U1 is connected to the source of the MOS tube and the common end is connected to one end of the resistor R6, and the switching power supply chip The seventh pin of U1 is connected to one end of the capacitor C5, the eighth pin of the switching power supply chip U1 is connected to one end of the resistor R3 and the common end is connected to one end of the capacitor C3, the other end of the capacitor C10 is connected to the other end of the capacitor C5, the other end of the capacitor C3, the other end of the resistor R6, and the other end of the resistor R8, and their common end is grounded, the other end of the resistor R3 is connected to the power supply VDD, the drain of the MOS tube is connected to the positive electrode of the diode D7 and the common end is connected to one end of the inductor L3, the other end of the inductor L3 is connected to the output end of the rectifier and filter circuit, and the common end is connected to the input end of the PFC circuit, the negative electrode of the diode D7 is connected to one end of the capacitor C7, and the common end is connected to the other end of the resistor R7 and the VDD power output terminal, and the other end of the capacitor C7 is grounded.

[0017] In a second aspect, the present invention provides a method for improving the power factor of a power supply, wherein the method for improving the power factor of a power supply is implemented by the circuit for improving the power factor of a power supply described in the first aspect.

[0018] Furthermore, the method for improving the power factor of a power supply comprises the following steps:

[0019] S1: The input AC power is shaped into pulsating DC power through the rectifier and filter circuit;

[0020] S2: PFC converts the pulsating direct current into alternating current, inverts and amplifies the alternating current, and then inputs it into the voltage feedback input pin of the switching power supply chip U1.

[0021] S3: The switching power supply chip U1 adjusts the output voltage value of the VDD power supply according to the input voltage of the voltage feedback input pin.

[0022] Furthermore, the step S3 specifically includes the following steps:

[0023] S301: When the AC input voltage is high, the voltage feedback input pin input voltage is low, and the switching power supply chip U1 increases the output voltage value of the VDD power supply;

[0024] S302: When the AC input voltage is low, the voltage feedback input pin input voltage is high, and the switching power supply chip U1 reduces the output voltage value of the VDD power supply.

[0025] The beneficial effects of the present invention are as follows: the present invention outputs a voltage with a phase opposite to that of the AC input voltage through the PFC circuit, so that the voltage feedback input pin of the switching power supply chip obtains a voltage with a phase opposite to that of the AC input voltage. The switching power supply chip increases or decreases the output voltage value of the VDD power supply according to the voltage of the voltage feedback input pin, and superimposes a waveform with the same phase as the rectified AC input voltage on VDD, so that the AC input current changes with the change of the voltage, thereby achieving the purpose of improving the power factor of the power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The invention is further described with reference to the accompanying drawings, but the embodiments in the accompanying drawings do not constitute any limitation to the invention. A person skilled in the art can obtain other drawings based on the following drawings without making any creative effort.

[0027] Figure 1 The present invention is a schematic diagram of a circuit structure of an embodiment of a circuit for improving the power factor of a power supply.

[0028] The reference numerals are as follows: 10. AC input module, 20. Rectification and filtering circuit, 30. PFC circuit, 40. Boost switching power supply main circuit. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0030] A circuit for improving the power factor of a power supply according to this embodiment includes:

[0031] AC input terminal ACIN: AC input module 10 AC input terminal ACIN, the input end of the AC input terminal ACIN is connected to the external AC power;

[0032] Rectifier and filter circuit 20: The input end of the rectifier and filter circuit 20 is connected to the output end of the AC input terminal ACIN. The rectifier and filter circuit 20 is used to convert the input AC power into DC power.

[0033] A PFC circuit 30, wherein the input end of the PFC circuit 30 is connected to the output end of the rectifier and filter circuit 20. The PFC circuit 30 constitutes an inverting amplifier circuit for inverting and amplifying the AC component of the pulsating low-frequency DC voltage output by the rectifier and filter circuit, and then outputting the AC component;

[0034] Boost switching power supply main circuit terminal 40: Boost switching power supply main circuit terminal 40 includes switching power supply chip U1 and peripheral circuit. The voltage feedback input pin of switching power supply chip U1 is connected to the output end of PFC circuit 30. Switching power supply chip U1 is connected to the peripheral circuit. The input end of the peripheral circuit is connected to the output end of rectifier filter circuit 20. Boost switching power supply main circuit terminal 40 outputs VDD power supply.

[0035] Among them, the rectifier and filter circuit 20 includes a diode D1, a diode D2, a diode D3, a diode D4, and a capacitor C1. The diode D1, the diode D2, the diode D3, and the diode D4 constitute a rectifier bridge. The input end of the rectifier bridge is connected to the AC input terminal ACIN, the first output end of the rectifier bridge is connected to one end of the capacitor C1 and the common end is connected to the PFC circuit 30, the second output end of the rectifier bridge is grounded, and the other end of the capacitor C1 is grounded.

[0036] The PFC circuit 30 includes a capacitor C2, a capacitor C4, a capacitor C12, a resistor R1, a resistor R2, a resistor R4, a resistor R9, a controllable precision voltage regulator U3, and a power supply VDD. One end of the capacitor C2 is connected to one end of the capacitor C1, the other end of the capacitor C2 is connected to one end of the resistor R4, the other end of the resistor R4 is connected to one end of the resistor R2, and the common end is connected to one end of the resistor R5, one end of the capacitor C12, and the control end of the controllable precision voltage regulator U3. One end of the resistor R5 is connected to the input end of the controllable precision voltage regulator U3, and the common end is grounded. The other end of the resistor R2 is connected to one end of the resistor R1, and the common end is connected to the other end of the capacitor C12, the output end of the controllable precision voltage regulator U3, and one end of the capacitor C4. The other end of the resistor R1 is connected to the power supply VDD, the other end of the capacitor C4 is connected to one end of the resistor R9, and the other end of R9 is connected to the Boost switching power supply main circuit terminal 40.

[0037] In this embodiment, the controllable precision voltage regulator U3 is specifically a TL431. The reference voltage of the TL431 is 2.5V. The control terminal of the TL431 is the G pin, the input terminal of the TL431 is the A pin, and the output terminal of the TL431 is the K pin. The voltage is divided by R2 and R5 and input to the G pin of the TL431. The DC operating potential of the K pin of the TL431 can be easily set to make the amplifier circuit operate in an optimal state. R2 also serves as the negative feedback resistor of the amplifier circuit. C12 is a negative feedback capacitor that filters out high-frequency interference. R1 is the load resistor of the amplifier circuit and provides power for the amplifier circuit and the output. It should be noted that the TL431 in the present invention is to form an inverting amplifier circuit. The same function can also be achieved using components such as transistors and operational amplifiers. In this embodiment, the TL431 is selected because it is easier to debug and has more stable operation. The voltage at the connection terminal of capacitor C2 and resistor R4 is the same as the AC input voltage. The gain A of the PFC circuit 30 is A=R2 / R4.

[0038] The boost switching power supply main circuit end 40 includes a switching power supply chip U1, a MOS tube Q2, a diode D7, an inductor L3, a resistor R3, a resistor R6, a resistor R7, a resistor R8, a capacitor C3, a capacitor C5, a capacitor C7, a capacitor C10 and a VDD power supply output terminal. The first pin of the switching power supply chip U1 is grounded, the third pin of the switching power supply chip U1 is connected to one end of the capacitor C10, the fourth pin of the switching power supply chip U1 is connected to the other end of the resistor R9 and the common end is connected to one end of the resistor R7 and one end of the resistor R8. The fifth pin of the first pin of the switching power supply chip U1 is connected to the gate of the MOS tube Q2, the sixth pin of the first pin of the switching power supply chip U1 is connected to the source of the MOS tube and the common end is connected to one end of the resistor R6. The seventh pin of the first pin of the power supply chip U1 is connected to one end of the capacitor C5, the eighth pin of the first pin of the switching power supply chip U1 is connected to one end of the resistor R3 and the common end is connected to one end of the capacitor C3, the other end of the capacitor C10 is connected to the other end of the capacitor C5, the other end of the capacitor C3, the other end of the resistor R6, the other end of the resistor R8 and their common end is grounded, the other end of the resistor R3 is connected to the power supply VDD, the drain of the MOS tube is connected to the positive electrode of the diode D7 and the common end is connected to one end of the inductor L3, the other end of the inductor L3 is connected to one end of the capacitor C1 and the common end is connected to one end of the capacitor C2, the negative electrode of the diode D7 is connected to one end of the capacitor C7 and the common end is connected to the other end of the resistor R7 and the VDD power output terminal, and the other end of the capacitor C7 is grounded.

[0039] The present invention operates as follows: After receiving the rectified current from the rectifier and filter circuit 10, capacitor C2 utilizes the capacitor's characteristic of blocking DC and passing AC to obtain an AC input voltage signal. This voltage signal is then limited by resistor R4 and fed to the G pin, the inverting input pin of the TL431. The amplification factor of the amplifier circuit is set appropriately by the ratio of R2 to R4. The reverse AC input voltage signal is obtained at the K pin of the TL431, blocked by C4 and limited by R9, and then connected to the fourth pin (i.e., the OVP voltage feedback input pin) of the switching power supply chip U1. When the AC input is high voltage, it is reduced to a low voltage after passing through the PFC circuit and connected to the fourth pin of the switching power supply chip U1, causing the fifth pin of the switching power supply chip U1 to increase the output voltage of the VDD power supply. The opposite occurs when the AC input is high voltage. This ensures that when the AC input is high, the VDD power supply's output voltage increases, and when the AC input is low, the VDD power supply's output voltage decreases. This means that a waveform with the same phase as the AC input voltage (strictly speaking, the waveform of the rectified input voltage) is superimposed on VDD, causing the AC input current to change with the voltage, thereby improving the power factor. The power factor can be adjusted by adjusting the value of resistor R9, reaching a maximum power factor of 0.9 or above.

[0040] Example 2: A method for improving the power factor of a power supply.

[0041] This embodiment provides a method for improving the power factor of a power supply. The method for improving the power factor of a power supply implemented by the circuit for improving the power factor of a power supply of this embodiment includes the following steps:

[0042] S1: The input AC power is shaped into pulsating DC power through the rectifier and filter circuit;

[0043] S2: PFC converts the pulsating DC power into AC power, inverts and amplifies the AC power, and then inputs it into the voltage feedback input pin of the switching power supply chip U1;

[0044] S3: The switching power supply chip U1 adjusts the output voltage value of the VDD power supply according to the input voltage of the voltage feedback input pin.

[0045] The specific steps of step S3 are:

[0046] S301: When the AC input voltage is high, the voltage feedback input pin input voltage is low, and the switching power supply chip U1 increases the output voltage value of the VDD power supply;

[0047] S302: When the AC input voltage is low, the voltage feedback input pin input voltage is high, and the switching power supply chip U1 reduces the output voltage value of the VDD power supply.

[0048] The above method realizes that when the AC input is high, the output voltage value of the VDD power supply is higher, and when the AC input is low, the output voltage value of the VDD power supply is reduced. That is, a waveform with the same phase as the AC input voltage (strictly speaking, the waveform after the input voltage is rectified) is superimposed on VDD, so that the AC input current changes with the voltage, thereby achieving the purpose of improving the power factor.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A circuit for improving the power factor of a power supply, characterized in that: include AC input terminal ACIN: the AC input terminal ACIN is connected to an external AC power source; Rectifier and filter circuit: The input end of the rectifier and filter circuit is connected to the AC input terminal ACIN, and the rectifier and filter circuit is used to convert the input AC voltage into a pulsating low-frequency DC voltage; a PFC circuit, wherein an input end of the PFC circuit is connected to an output end of the rectifier and filter circuit, and the PFC circuit constitutes an inverting amplifier circuit for inverting and amplifying an AC component in the pulsating low-frequency DC voltage output by the rectifier and filter circuit; Boost switching power supply main circuit: The Boost switching power supply main circuit includes a switching power supply chip U1 and its peripheral circuits. The fourth pin of the switching power supply chip U1 is connected to the output end of the PFC circuit. The switching power supply chip U1 is connected to the peripheral circuit. The input end of the peripheral circuit is connected to the output end of the rectifier and filter circuit. The Boost switching power supply main circuit outputs the VDD power supply. The PFC circuit includes a capacitor C2, a capacitor C4, a capacitor C12, a resistor R1, a resistor R2, a resistor R4, a resistor R9, a controllable precision voltage regulator U3, and a power supply VDD. One end of the capacitor C2 is connected to the output end of the rectifier and filter circuit, the other end of the capacitor C2 is connected to one end of the resistor R4, the other end of the resistor R4 is connected to one end of the resistor R2, and the common end is connected to one end of the resistor R5, one end of the capacitor C12, and the control end of the controllable precision voltage regulator U3. One end of the resistor R5 is connected to the input end of the controllable precision voltage regulator U3, and the common end is grounded. The other end of the resistor R2 is connected to one end of the resistor R1, and the common end is connected to the other end of the capacitor C12, the output end of the controllable precision voltage regulator U3, and one end of the capacitor C4. The other end of the resistor R1 is connected to the power supply VDD, the other end of the capacitor C4 is connected to one end of the resistor R9, and the other end of R9 is connected to the Boost switching power supply main circuit.

2. A circuit for improving the power factor of a power supply as claimed in claim 1, characterized in that: The rectifier and filter circuit includes a diode D1, a diode D2, a diode D3, a diode D4, and a capacitor C1. The diode D1, the diode D2, the diode D3, and the diode D4 constitute a rectifier bridge. The input end of the rectifier bridge is connected to the AC input terminal ACIN, the first output end of the rectifier bridge is connected to one end of the capacitor C1, and the common end is connected to the PFC circuit and the Boost boost switching power supply main circuit. The second output end of the rectifier bridge is grounded, and the other end of the capacitor C1 is grounded.

3. A circuit for improving the power factor of a power supply as claimed in claim 1, characterized in that: The gain of the PFC circuit is A=R2 / R4.

4. A circuit for improving the power factor of a power supply as claimed in claim 1, characterized in that: The controllable precision voltage regulator U3 is specifically TL431.

5. A circuit for improving the power factor of a power supply as claimed in claim 1, characterized in that: The voltage at the connection terminal between the capacitor C2 and the resistor R4 is the same as the AC input voltage.

6. A circuit for improving the power factor of a power supply as claimed in claim 1, characterized in that: The Boost switching power supply main circuit includes a switching power supply chip U1, a MOS tube Q2, a diode D7, an inductor L3, a resistor R3, a resistor R6, a resistor R7, a resistor R8, a capacitor C3, a capacitor C5, a capacitor C7, a capacitor C10 and a VDD power supply output terminal. The first pin of the switching power supply chip U1 is grounded, the third pin of the switching power supply chip U1 is connected to one end of the capacitor C10, the fourth pin of the switching power supply chip U1 is connected to the output end of the PFC circuit and the common end is connected to one end of the resistor R7 and one end of the resistor R8, the fifth pin of the switching power supply chip U1 is connected to the gate of the MOS tube Q2, the sixth pin of the switching power supply chip U1 is connected to the source of the MOS tube and the common end is connected to one end of the resistor R6, and the switching power supply chip U1 is connected to the gate of the MOS tube Q2. The seventh pin is connected to one end of the capacitor C5, the eighth pin of the switching power supply chip U1 is connected to one end of the resistor R3 and the common end is connected to one end of the capacitor C3, the other end of the capacitor C10 is connected to the other end of the capacitor C5, the other end of the capacitor C3, the other end of the resistor R6, the other end of the resistor R8, and their common end is grounded, the other end of the resistor R3 is connected to the power supply VDD, the drain of the MOS tube is connected to the positive electrode of the diode D7 and the common end is connected to one end of the inductor L3, the other end of the inductor L3 is connected to the output end of the rectifier and filter circuit, and the common end is connected to the input end of the PFC circuit, the negative electrode of the diode D7 is connected to one end of the capacitor C7, and the common end is connected to the other end of the resistor R7 and the VDD power output terminal, and the other end of the capacitor C7 is grounded.

7. A method for improving the power factor of a power supply, characterized in that: The method for improving the power factor of a power supply is implemented by the circuit for improving the power factor of a power supply according to any one of claims 1 to 6.

8. A method for improving the power factor of a power supply according to claim 7, characterized in that: The method for improving the power factor of a power supply comprises the following steps: S1: The input AC power is shaped into pulsating DC power through the rectifier and filter circuit; S2: PFC converts the pulsating DC power into AC power, inverts and amplifies the AC power, and then inputs it into the voltage feedback input pin of the switching power supply chip U1; S3: The switching power supply chip U1 adjusts the output voltage value of the VDD power supply according to the input voltage of the voltage feedback input pin.

9. A method for improving the power factor of a power supply according to claim 8, characterized in that: The step S3 specifically includes the following steps: S301: When the AC input voltage is high, the voltage feedback input pin input voltage is low, and the switching power supply chip U1 increases the output voltage value of the VDD power supply; S302: When the AC input voltage is low, the voltage feedback input pin input voltage is high, and the switching power supply chip U1 reduces the output voltage value of the VDD power supply.

Images