Valley-filling power factor correction circuit with EMI protection function

Abstract

The power control circuit includes an AC power source, a rectifier, and a valley-filling circuit. The AC power source receives an AC voltage, and the rectifier converts the AC voltage into a rectified voltage. The valley-filling circuit includes: an inductor having a first terminal coupled to the rectifier and a second terminal; a first resistor having a first terminal coupled to the second terminal of the inductor and a second terminal; a diode having a cathode coupled to the second terminal of the inductor and an anode; and a first capacitor having a first terminal coupled to the second terminal of the first resistor and the anode of the diode, and a second terminal coupled to the ground.

Description

Technical Field

[0001] The present invention relates to a passive valley-fill power factor correction (PFC) architecture that converts an AC voltage into a DC voltage, and more particularly to improvements in electromagnetic interference (EMI) of a switching-mode power supply (SMPS). Background Art

[0002] Power factor is important for determining whether electronic products are working efficiently. Power factor can be calculated by comparing real power with apparent power. Real power is used to indicate the effectiveness of work and only includes the real component of the AC power, while apparent power is the average product of current and voltage, including the real and imaginary components of the AC power.

[0003] When generating the same amount of available power, a power system with a lower power factor consumes more circulating current than a power system with a higher power factor because the power returned to the load is larger, resulting in increased power losses in the distribution system as a whole. In other words, a lower power factor means lower operating efficiency, which results in the need for a larger capacity and more conductors for the device. According to the ENERGY STAR Lamps V2.1 Final Specification, the requirement for lighting products with a total output power of less than 5 watts is that the power factor must be greater than 0.5, and the requirement for lighting products with a total output power of more than 5 watts is that the power factor must be greater than 0.7.

[0004] The valley-fill circuit plays an important role in adjusting the power factor of the product. It is a passive power factor correction (PFC) circuit. Figure 1A , which is a schematic diagram of an existing power factor control circuit 100, such as Figure 1AAs shown, the power factor control circuit 100 includes an AC power source 10, a diode-bridge rectifier 15, an EMI module 20, a valley-filling circuit 30, a switching-mode power supply (SMPS) 40, and an LED array 50. The EMI module 20 is coupled to the AC power source 10 and is used to reduce EMI emissions. The valley-filling circuit 30 is coupled to the EMI module 20 and is used to improve the power factor of the power factor control circuit 100. However, many passive components are provided in the power factor control circuit 100, so the valley-filling circuit 30 and the EMI module 20 are required to improve the power factor and reduce the EMI emissions respectively.

[0005] In addition, when an AC voltage is applied to the power factor control circuit 100, the rectified voltage is applied to a plurality of capacitors (eg, capacitor C V1 , C V2 ) until it reaches nearly half of the line voltage peak (reference Figure 1A If the operation is in the valley phase, it means that the line voltage drops below the peak voltage. At this time, C V1 and C V2 will discharge to the load (reference Figure 1B Furthermore, the power factor control circuit 100 is charged in series and discharged in parallel, which results in current asymmetry and may lead to more severe total harmonic distortions (THD). In summary, there is a need for a novel method and architecture to improve the overall power factor of an SMPS driver for an electronic device (such as a lighting device). Summary of the invention

[0006] An embodiment of the present invention provides a power control circuit, which includes an alternating current (AC), a rectifier, and a valley-fill circuit. The AC power is used to receive an AC voltage; the rectifier is used to convert the AC voltage into a rectified voltage; and the valley-fill circuit includes: an inductor having a first terminal coupled to the rectifier and a second terminal; a first resistor having a first terminal coupled to the second terminal of the inductor and a second terminal; a diode having a cathode coupled to the second terminal of the inductor and an anode; and a first capacitor having a first terminal coupled to the second terminal of the first resistor and the anode of the diode, and a second terminal coupled to the ground. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1A It is a schematic diagram of an existing power factor control circuit.

[0008] Figure 1B for Figure 1A A schematic diagram of the discharge operation of a conventional power factor control circuit is shown in FIG.

[0009] Figure 2 FIG. 4 is a schematic diagram of a power factor control circuit according to an embodiment of the present invention.

[0010] Figure 3 FIG. 4 is a schematic diagram of a power factor control circuit according to another embodiment of the present invention.

[0011] Figure 4 for Figure 3 Schematic diagram of the output of the valley-filling circuit shown in FIG.

[0012] Figure 5 FIG. 4 is a schematic diagram of a power factor control circuit according to another embodiment of the present invention.

[0013] Reference numerals list

[0014] 100, 200, 300, 500 power factor control circuit

[0015] 10 AC power supply

[0016] 15 Diode-Bridge Rectifier

[0017] 20 EMI Module

[0018] 30 Valley Fill Circuit

[0019] 40 Switch Mode Power Supply

[0020] 50 LED Array

[0021] D, D1, D2, D3 diodes

[0022] R v , R F Resistors

[0023] C V , C V1 , C V2 , C F1 , C F2 Capacitors

[0024] V OUT Output voltage

[0025] V rec Voltage Node

[0026] L Inductor

[0027] D Diode

[0028] 210 AC current source

[0029] 220 Fuse

[0030] 230 Metal Oxygen Varistor Unit

[0031] 240 Rectifier Circuit

[0032] 250 Switch Mode Power Supply

[0033] 260 LED Array

[0034] 270, 370, 570 valley-fill circuits

[0035] Vm Voltage peak

[0036] V1, V2, V LED_max Voltage value

[0037] t1, t2 time points DETAILED DESCRIPTION

[0038] Certain words are used in the specification and subsequent patent applications to refer to specific components. It should be understood by those with ordinary knowledge in the field that hardware manufacturers may use different terms to refer to the same component. This specification and subsequent patent applications do not use differences in names as a way to distinguish components, but rather use differences in the functions of components as the criteria for distinction. The term "including" mentioned throughout the specification and subsequent claims is an open term and should be interpreted as "including but not limited to". In addition, the term "coupled" herein includes any direct and indirect electrical connection means. Therefore, if the text describes a first device coupled to a second device, it means that the first device can be directly electrically connected to the second device, or indirectly electrically connected to the second device through other devices or connection means.

[0039] The above-mentioned prior art solutions (or prior art solutions) achieve the required power control capability at the cost of increasing the design complexity, increasing the number of passive components (which will correspondingly require a larger circuit area), etc., while the novel circuit design provided by the embodiments of the present invention has reduced cost and simplified complexity.

[0040] Please refer to Figure 2 , Figure 2 FIG. 2 is a schematic diagram of a power factor control circuit 200 according to an embodiment of the present invention. Figure 2 As shown, inductor L, diode D, resistor R V and capacitor C V They can be collectively regarded as an integrated EMI valley-filling circuit (i.e., valley-filling circuit 270) to provide ideal technical effects without the aforementioned disadvantages. In addition to valley-filling circuit 270, power factor control circuit 200 also includes AC current source 210, fuse 220, metal-oxide varistor (MOV) unit 230, rectifier circuit 240, switching-mode power supply (SMPS) 250, and LED array 260. As long as the same / similar technical effects can be achieved, Figure 2 Some components depicted in the figure may be omitted according to actual design requirements.

[0041] The metal oxide varistor 230 is an electronic component with a resistance value, and its resistance value varies with the applied voltage. The metal oxide varistor 230 is also called a voltage-dependent resistor (VDR), which has a nonlinear, non-ohmic current-voltage characteristic, so it is similar to a diode. In contrast to a diode, a varistor has the same characteristics in both lateral current directions. The metal oxide varistor 230 can be used as a control or compensation component in the power factor control circuit 200 to provide optimized operating conditions or to provide prevention and control for excessive transient voltages.

[0042] The rectifier circuit 240 may be a diode-bridge rectifier (or bridge rectifier). For example (but not limited to), a diode bridge rectifier is a bridge circuit configuration composed of four diodes, which provides the same polarity to the output as the input. Bridge rectifiers are widely used to convert AC current input to DC current output.

[0043] The switch mode power supply 250 converts power by frequently turning on / off the switch device, and uses a storage element (such as an inductor or a capacitor) to supply power when the switch device is in a non-conductive state. SMPS can be used to power many devices, such as computer equipment, sensitive electronic equipment, devices that rely on battery power, and other devices that require high-efficiency power supply.

[0044] Furthermore, the inductor L and the capacitor C V The configuration can provide EMI suppression capability (EMI-suppressing ability) for the power factor control circuit 200, and the diode D and the resistor R V and capacitor C V The configuration can provide a valley filling function for the power factor control circuit 200, wherein the diode D and the resistor R V and capacitor C V The combination of R V 、Capacitor C V And the function of diode D3. Compared with Figure 1A / Figure 1B The charge / discharge method shown, Figure 2 The charging / discharging method shown can further improve the symmetry performance, thereby solving the technical problems faced by the prior art.

[0045] Please refer to Figure 3 , Figure 3FIG. 2 is a schematic diagram of a power factor control circuit 300 according to another embodiment of the present invention. The difference between the power factor control circuit 300 and the power factor control circuit 200 is that the valley-filling circuit 370 in the power factor control circuit 300 further includes a resistor R F and capacitor C F1 . Capacitor C F1 , inductor L and capacitor C V The combination of forms a π-type EMI circuit, which can provide better EMI suppression characteristics.

[0046] To ensure that the switch mode power supply 250 receives an optimized input voltage, such as Figure 4 The rectified sine wave output by the valley-fill circuit 370 is shown in FIG. V The capacitance value should be further designed to meet specific conditions to Figure 4 For example, the horizontal dotted line represents the voltage provided to the LED array 260, which is V LED_max The rising portion of the jagged dashed line represents a charging period, and the falling portion of the jagged dashed line represents a holding period. LED_max Nearly constant can provide a carefully designed C V Value (the italic C V Represents capacitor C V Capacitance value), where C V The value can be derived from the following formula:

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[0054] Please refer to Equation 1, C V must be greater than or equal to a given value so that the LED array 260 can obtain the required power supply voltage, where ΔV C V C The voltage change, I load,max Represents the maximum current of the output load, V m,min Represents the voltage amplitude V mThe minimum value of the peak value, and t Hold represents the capacitor discharge time, which can be calculated by Equation 2. In Equation 3, the capacitor charging time t chg This can be obtained by subtracting t from the period 1 / 2f Hold Come get it. chg is defined in Equation 4, and the result in Equation 6 can be simply derived from Equation 4 and Equation 5. In addition, I chg represents the charging current, and R V Represents the resistor R V Finally, the result in Equation 7 can be obtained by substituting Equation 6 into Equation 1.

[0055] Figure 5 is a schematic diagram of a power factor control circuit 500 according to another embodiment of the present invention. The difference between the power factor control circuit 300 and the power factor control circuit 500 is that in the power factor control circuit 500, the valley filling circuit 570 further includes a capacitor C F2 , which helps to further provide optimized output. Some components in this embodiment are the same or similar to those in the above embodiments, and detailed descriptions are omitted here for the sake of brevity.

[0056] As described above, the embodiments of the present invention can improve the overall power factor of the power control circuit and provide EMI suppression capability with reduced cost and simplified complexity. For example, the embodiments of the present invention adopt the design of an integrated EMI valley filling circuit, which requires only fewer components and does not affect the desired technical effect (compared to Figure 1A , 1B solutions in the prior art).

[0057] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A power control circuit, comprising: an AC power source configured to receive an AC voltage; a rectifier configured to convert the AC voltage into a rectified voltage; Valley-fill circuit, including: an inductor having a first terminal coupled to the rectifier and having a second terminal; A first resistor having a first terminal coupled to the second terminal of the inductor and having a second terminal; a diode having a cathode coupled to the second terminal of the inductor and an anode; as well as a first capacitor having a first terminal coupled to the second terminal of the first resistor and the anode of the diode, and having a second terminal coupled to the ground terminal, The first capacitor is charged through the inductor and the first resistor, and the first capacitor is discharged through the diode.

2. The power control circuit as claimed in claim 1, wherein the rectifier is a diode-bridge rectifier.

3. The power control circuit as claimed in claim 1, wherein the valley-fill circuit is further coupled to a DC-DC converter to provide a constant current output or a constant current output to the LED driving circuit. 4 . The power control circuit as claimed in claim 3 , wherein a switch mode power supply is coupled between the valley filling circuit and the LED driving circuit.

5. The power control circuit as claimed in claim 1, further comprising: A metal-oxygen varistor unit is coupled between the AC power source and the rectifier; and A fuse is coupled between the AC power source and the metal-oxygen varistor unit.

6. The power control circuit as claimed in claim 1, wherein the valley filling circuit further comprises: a second resistor having a first terminal coupled to the first terminal of the inductor and a second terminal coupled to the first terminal of the first resistor; and The second capacitor has a first terminal coupled to the first terminal of the second resistor and a second terminal coupled to the ground.

7. The power control circuit as claimed in claim 6, wherein the valley filling circuit further comprises: The third capacitor has a first terminal coupled to the first terminal of the first resistor and a second terminal coupled to the ground.

8. The power control circuit as claimed in claim 1, wherein the output of the valley-fill circuit is in the form of a rectified sine wave.

9. The power control circuit as claimed in claim 8, wherein the capacitance of the first capacitor satisfies the following equation: Among them C V represents the capacitance value of the first capacitor, ΔV C Represents the capacitance value V C The voltage change, I load,max Represents the maximum current value on the output load end, V m,min Represents the voltage amplitude V m The minimum value of the peak value, t Hold Represents the discharge time of the capacitor, t chg Represents the charging time of the capacitor, I chg represents the charging current, and R V represents the resistance value of the first resistor.

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