TWI724777B - Power control circuit - Google Patents

Abstract

A power control circuit includes an alternating current (AC) power source, a rectifier and a valley-fill circuit. The AC power source is configured to receive an AC voltage. The rectifier is configured to convert the AC voltage into a rectified voltage. 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 ground.

Description

Power control circuit

The present invention relates to a passive valley-fill (valley-fill) power factor correction (PFC) architecture, which converts AC voltage to DC voltage, especially regarding switching-mode power supply (SMPS) Improvements in electromagnetic interference (EMI).

The power factor is very important for judging whether the electronic product works effectively. The power factor can be calculated by comparing the real power with the apparent power. Real power is used to express the effectiveness of work and only includes the real component of AC power, while apparent power is the average product of current and voltage, including the real and imaginary components of AC power.

In the case of generating usable power of the same size, a power system with a lower power factor will consume more circulating current than a power system with a higher power factor, because the power returned to the load is larger , Resulting in an increase in the overall power loss of the distribution system. In other words, a lower power factor means that the operating efficiency is also lower, which causes the device to require a larger capacity and more conductors. According to the ENERGY STAR Lamps V2.1 Final Specification, for lighting products with a total output power of less than 5 watts (watts), the power factor must be greater than 0.5, and for lighting products with a total output power greater than 5 watts The rule is power The factor must be greater than 0.7.

The valley-fill circuit plays an important role in adjusting the power factor of the product, and it is a passive power factor correction (PFC) circuit. Please refer to Figure 1A, which is a schematic diagram of a conventional power factor control circuit 100. As shown in Figure 1A, the power factor control circuit 100 includes an AC power supply 10 and a diode-bridge rectifier. 15. EMI module 20, valley filling circuit 30, switching-mode power supply (SMPS) 40, and LED array 50. The EMI module 20 is coupled to the AC power supply 10 and is used to reduce EMI emissions. The valley filling circuit 30 is coupled to the EMI module 20 and used to improve the power factor of the power factor control circuit 100. However, there are many passive components 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 EMI emissions, respectively.

In addition, when AC voltage is applied to the power factor control circuit 100, the rectified voltage will charge multiple capacitors (such as capacitors C _V1 , C _V2 ) through D2 and Rv until it is charged to half of the peak value of the near-line voltage (see section The charging direction shown by the dotted arrow in Figure 1A). If it is operating in the valley phase, it means that the line voltage drops below the voltage peak value. At this time, C _V1 and C _V2 will be discharged to the load (refer to the discharge direction shown by the dashed arrow in Figure 1B). Furthermore, the power factor control circuit 100 is charged in series and discharged in parallel, which causes current asymmetry, which may lead to more serious total harmonic distortions (THD). In summary, there is a need for a novel method and architecture to improve the overall power factor of SMPS drivers applied to electronic devices (such as lighting devices).

An embodiment of the present invention provides a power control circuit, which includes an AC power supply (alternating current, AC), rectifier and valley-fill circuit. The AC power supply is used for receiving an AC voltage; the rectifier is used for converting the AC voltage into a rectified voltage; and the valley-filling circuit includes: an inductor having a first terminal coupled to the Rectifier, and has a second terminal; a first resistor, has a first terminal, which is coupled to the second terminal of the inductor, and has a second terminal; a diode, Having a cathode coupled to the second end of the inductor and having an anode; and a first capacitor having a first end coupled to the second end of the first resistor Point and the anode of the diode, and have a second terminal, which is coupled to the ground terminal.

100, 200, 300, 500: power factor control circuit

10: AC power

15: Diode-bridge rectifier

20: EMI module

30: Valley-filling circuit

40: switch mode power supply

50: LED array

D, D1, D2, D3: Diode

Rv, R _F : resistor

C _V , C _V1 , C _V2 , C _F1 , C _F2 : Capacitor

V _OUT : output voltage

V _rec : voltage node

L: Inductor

D: Diode

210: AC current source

220: fuse

230: Metal Oxygen Varistor Unit

240: rectifier circuit

250: switch mode power supply

260: LED array

270,370,570: Valley-filling circuit

Vm: peak voltage

V1, V2, V _{LED_max} : voltage value

t1, t2: time point

Figure 1A is a schematic diagram of a conventional power factor control circuit.

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

FIG. 2 is a schematic diagram of a power factor control circuit according to an embodiment of the invention.

FIG. 3 is a schematic diagram of a power factor control circuit according to another embodiment of the invention.

Figure 4 is a schematic diagram of the output of the valley filling circuit shown in Figure 3.

Fig. 5 is a schematic diagram of a power factor control circuit according to another embodiment of the present invention.

In the specification and subsequent patent applications, certain words are used to refer to specific elements. Those with general knowledge in the field should understand that hardware manufacturers may use different terms to refer to the same components. The scope of this specification and subsequent patent applications does not use differences in names as a way of distinguishing elements, but uses differences in functions of elements as a criterion for distinguishing. The "include" mentioned in the entire manual and subsequent requests is an open term, so it should be interpreted as "includes Including but not limited to". In addition, the term "coupling" here includes any direct and indirect electrical connection means. Therefore, if it is described that a first device is 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.

The above-mentioned conventional technology solution (or conventional technology solution) is to achieve the required under the condition of increasing cost, increasing design complexity, increasing the number of passive components (which will correspondingly require larger circuit area), etc. Power control capability, and the novel circuit design provided by the embodiments of the present invention has reduced cost and simplified complexity.

Please refer to FIG. 2, which is a schematic diagram of a power factor control circuit 200 according to an embodiment of the present invention. As shown in Figure 2, the inductor L, the diode D, the resistor R _V, and the capacitor C _V can be collectively regarded as an integrated EMI valley-filling circuit (that is, valley-filling circuit 270). In the case of shortcomings, the ideal technical effect can still be provided. In addition to the valley filling circuit 270, the power factor control circuit 200 also includes an AC current source 210, a fuse 220, a metal-oxide varistor (MOV) unit 230, a rectifier circuit 240, and a switching-mode power supply (switching-mode power supply). supply, SMPS) 250 and LED array 260. As long as the same/similar technical effects can be achieved, some elements depicted in Figure 2 may be omitted based on actual design requirements.

The gold-oxygen varistor 230 is an electronic component with a resistance value, and its resistance value will vary with the applied voltage. The gold-oxygen varistor 230 is also called a voltage-dependent resistor (VDR), which has non-linear and non-ohmic current-voltage characteristics, so it is similar to a diode . In contrast to diodes, varistors have the same characteristics in both lateral current directions. The gold-oxygen varistor 230 can be used as a control or in the power factor control circuit 200 Compensation components to provide optimized operating conditions or provide protection against excessive transient voltages.

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

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

Furthermore, the configuration of the inductor L and the capacitor C _V can provide the power factor control circuit 200 with EMI suppression (EMI-suppressing ability), and the configuration of the diode D, the resistor R _V and the capacitor C _V can be power The factor control circuit 200 provides a valley filling function, wherein the combination of the diode D, the resistor R _V and the capacitor C _V can provide a function similar to that of the R _V , the capacitor C _V and the diode D3 shown in FIG. 1. Compared with the charging/discharging method shown in FIG. 1A/FIG. 1B, the charging/discharging method shown in FIG. 2 can further improve the symmetry performance, thereby solving the technical problems faced by the conventional art.

Please refer to FIG. 3, which 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 a capacitor C _F1 . The combination of capacitor C _F1 , inductor L and capacitor C _V constitutes a π-type EMI circuit, which can provide better EMI suppression characteristics.

In order to ensure that the switched-mode power supply 250 receives the optimized input voltage, such as the rectified sine wave output by the valley-fill circuit 370 shown in Figure 4, _{the capacitance value of the capacitor C V} should be further designed to meet specific conditions Taking Figure 4 as an example, the horizontal dashed line represents the voltage supplied to the LED array 260, and its magnitude is V _{LED_max} . The rising part of the zigzag dashed line represents a charging period, and the falling part of the zigzag dashed line represents the holding period. The _{nearly constant V LED_max} can provide a carefully designed C _V value (where C _{V in} italics represents the capacitance value of the capacitor C _V ), where the C _V value can be derived from the following equation:

Please refer to Equation 1. C _V must be greater than or equal to a given value to enable the LED array 260 to obtain the required power supply voltage, where △V _C represents the voltage change of V _{C , and I load,max} represents the maximum current of the output load. V _m,min represents the minimum value of the peak value of the voltage amplitude V _{m , and t Hold} represents the capacitor discharge time, which can be calculated by Equation 2. In Equation 3, the capacitor charging time t _chg can be obtained by subtracting t _Hold from the period 1/2f. I _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 resistance value of the resistor _{R V.} Finally, the result in Equation 7 can be obtained by substituting Equation 6 into Equation 1.

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 also A capacitor C _{F2 is} included, which helps to further provide an optimized output. Some components in this embodiment are the same or similar to those in the above embodiments, and for the sake of brevity, detailed descriptions are omitted here.

As described above, the embodiments of the present invention can improve the overall power factor of the power supply control circuit and provide EMI suppression capabilities with reduced cost and simplified complexity. For example, the embodiment of the present invention adopts the design of an integrated EMI valley-filling circuit, which only requires fewer components and does not affect the desired technical effect (compared to the solution of the prior art in Figures 1A and 1B) Program).

The foregoing descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made in accordance with the scope of the patent application of the present invention should fall within the scope of the present invention.

200: Power factor control circuit

D: Diode

Rv: resistor

C _V : Capacitor

V _OUT : output voltage

V _rec : voltage node

L: Inductor

D: Diode

210: AC current source

220: fuse

230: Metal Oxygen Varistor Unit

240: rectifier circuit

250: switch mode power supply

260: LED array

270: Valley Filling Circuit

Claims (10)

A power supply control circuit includes: an alternating current (AC) power supply configured to receive an AC voltage; a rectifier configured to convert the AC voltage into a rectified voltage; and a valley-fill circuit (valley-fill) circuit), including: an inductor with a first terminal coupled to the rectifier and a second terminal; a first resistor with a first terminal coupled to the rectifier The second terminal of the inductor has a second terminal; a diode has a cathode coupled to the second terminal of the inductor and has 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 terminal. The power control circuit according to claim 1, wherein the rectifier is a diode-bridge rectifier. The power control circuit according to claim 1, wherein the valley-filling circuit is additionally coupled to a DC-to-DC converter to provide a constant current output or a constant current output to an LED driving circuit Current output. The power control circuit according to claim 3, wherein a switching-mode power supply (SMPS) is coupled to the valley-fill circuit and the LED Between the drive circuits. The power control circuit according to claim 1, further comprising: a metal-oxide varistor (MOV) unit, coupled between the AC power source and the rectifier; and a fuse, coupled to Between the AC power supply and the MOV unit. The power control circuit according to claim 1, wherein the valley-filling circuit further comprises: a second resistor having a first terminal, which is coupled to the first terminal of the inductor, and having a A second terminal coupled to the first terminal of the first resistor; and a second capacitor having a first terminal coupled to the first terminal of the second resistor , And has a second terminal, which is coupled to the ground terminal. The power control circuit according to claim 6, wherein the valley-filling circuit further comprises: a third capacitor having a first terminal, which is coupled to the first terminal of the first resistor, and having A second terminal, which is coupled to the ground terminal. The power control circuit according to claim 1, wherein the output of the valley-filling circuit is in the form of a rectified sine wave. The power supply control circuit according to claim 8, wherein the capacitance value of the first capacitor satisfies the following equation:

Where C _V represents the capacitance value of the first capacitor, △V _C represents the voltage change of the capacitance value V _{C , I load,max} represents the maximum current value on the output load terminal, and V _m,min represents the peak value of the voltage amplitude V _m At the minimum 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. The power control circuit according to claim 1, wherein the first capacitor is charged through the inductor and the first resistor, and the first capacitor is discharged through the diode.

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