Patent Application
20210376714
This application claims priority to and the benefit of Taiwan Application Series Number 109118312 filed on Jun. 1, 2020, which is incorporated by reference in its entirety.
The present disclosure relates generally to active power-factor correction (PFC), and more particularly to active PFC circuits and relevant control methods that use a multifunctional signal at a multifunctional node for both over current protection and zero current detection.
PFC is a technique to increase the power factor of a load powered by an AC power source. PFC mainly modifies output current from the AC power source to the load, making the input current substantially in phase with the AC voltage of the AC power source. The maximum of power factor of a load is 1, meaning that the load to the AC power source is seemingly a pure resistor. A power supply with a low or bad power factor may harshly drain a huge amount of current from an AC power source in a very short time, and hardly utilizes the full power that the AC power source can supply. PFC may change the output current of the AC power source, to smooth its waveform and to increase its power factor.
Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following drawings. In the drawings, like reference numerals refer to like parts throughout the various figures unless otherwise specified. These drawings are not necessarily drawn to scale. Likewise, the relative sizes of elements illustrated by the drawings may differ from the relative sizes depicted.
The invention can be more fully understood by the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
According to embodiments of the invention, a PFC controller controls a power switch connected in series with an inductor to perform PFC. The PFC controller is a packaged monolithic integrated circuit chip, having a multifunctional pin electrically connected to a signal-integration circuit, which connects to both a drain and a source of the power switch. Based on a multifunctional signal at the multifunctional pin, the PFC controller detects an inductor current through the inductor when the power switch is turned ON, and detects a zero-current moment when the power switch is turned OFF, where the zero-current moment represents the moment when the inductor current drops to about zero. When the power switch is turned OFF, the PFC controller can also provide protections against disasters possibly caused by abnormal conditions.
Bridge rectifier BR provides full-wave rectification, to provide a direct-current (DC) input power source VIN and a ground line based on AC power source VAC-IN. Inductor L is electrically connected between input power source VIN and drain D. The combination of inductor L and decouple capacitor 201 results in a low-pass filter, making input current IIN smooth. According to embodiments, PFC controller 202 is a monolithic integrated circuit chip packaged with pins, and each pin is also a node for interconnecting electric devices. PFC controller 202 utilizes pulse-width-modulation technology to provide at drive pin DRV gate signal VG. Gate signal VG, as it controls gate G of power switch 204, turns ON and OFF power switch 204 to regulate output voltage VOUT and at the same time to make input current IIN substantially in phase with the voltage of AC power source VAC-IN, thereby achieving PFC. According to embodiments of the invention, PFC circuit 200 could operate in boundary mode, discontinuous conduction mode (DCM) or burst mode. Output voltage VOUT could supply power to loads or other power converters not shown in
Signal-integration circuit 206 is electrically connected to both drain D and source S, capable of integrating current-sense signal VCS and drain signal VD to generate multifunctional signal VCS/ZCD at multifunctional pin CS/ZCD of PFC controller 202. Signal-integration circuit 206 has a pair of resistors, R1 and R2, and a pair of capacitors Cl and C2. Resistors R1 and R2 are connected in series between drain D and source S, and so are capacitors C1 and C2. Joint 210 electrically connects resistors R1 and R2 and capacitors C1 and C2 to multifunctional pin CS/ZCD. Multifunctional signal VCS/ZCD represents current-sense signal VCS when power switch 204 is turned ON, because in the meantime drain signal VD is about the same with current-sense signal VCS. Therefore, based on the information that multifunctional signal VCS/ZCD carries when power switch 204 is ON, PFC controller 202 can acknowledge whether inductor current IL is too much and renders corresponding protection. On the occasion when power switch 204 is OFF, performing an open circuit between drain D and source S, multifunctional signal VCS/ZCD can represent drain signal VD because in the meantime current-sense signal VCS is about zero. Drain signal VD reflects output voltage VOUT when diode D1 forwards inductor current IL to output capacitor COUT, and drain signal VD starts oscillating after inductor current IL depletes or becomes zero. The moment when inductor current IL becomes zero is hereinafter referred to as zero-current moment tZCD. Accordingly, based on the information that multifunctional signal VCS/ZCD carries when power switch 204 is OFF, PFC controller 202 can detect output voltage VOUT and zero-current moment tZCD, to provide corresponding controls.
Please reference both
Pulse-width modulator 312 generates PWM signal SPWM, and driver 314, in response to PWM signal SPWM, provides gate signal VG with suitable voltage or current to drive power switch 204. In view of the logic values, gate signal VG and PWM signal SPWM in
During ON time TON, power switch 204 performs as a short circuit between drain D and source S. Therefore, inductor current IL and current-sense signal VCS both increase linearly over time. Because drain D electrically shorts to source S, drain signal VD is substantially equal to current-sense signal VCS, making multifunctional signal VCS/ZCD substantially equal to current-sense signal VCS if the input impedance into multifunctional pin CS/ZCD of PFC controller 202 is high. As shown in
Over-current detector 306 in
Similar with over-current detector 306, diode-short detector 308 compares multifunctional signal VCS/ZCD with diode-short-circuit protection (DSCP) reference signal VDSCP, another predetermined signal, during ON time TON. When multifunctional signal VCS/ZCD exceeds DSCP reference signal VDSCP, diode-short detector 308 provides protection signal SDSCP to disable pulse-width modulator 312, which in response quickly turns OFF power switch 204 and keeps it constantly OFF ever since. Diode-short detector 308 is used to protect power switch 204 from conducting over-large current when diode D1 mistakenly becomes a short circuit all the time and constantly clamps drain signal VD at output voltage VOUT.
During OFF time TOFF, current-sense signal VCS is about zero because power switch 204 conducts no current, so multifunctional signal VCS/ZCD, currently in proportion to drain signal VD, can represent drain signal VD, as shown in
During OFF time TOFF, zero-current detector 302 detects zero-current moment tZCD based on multifunctional signal VCS/ZCD, where zero-current moment tZCD refers to the moment when inductor current IL drops to about 0A, as shown in
During OFF time TOFF and after zero-current moment tZCD, valley detector 304 detects the occurrences of signal valleys VL1, VL2, etc., that drain voltage VD at drain D oscillates to create, and generates signal SV accordingly to pulse-width modulator 312, which is configured to start the next ON time TON at about the moment when the bottom of a signal valley appears, performing valley switching. Since the bottom of a signal valley means that the voltage difference between drain D and source S is at its minimum, valley switching can reduce conduction loss of power switch 204 and improve conversion efficiency. As shown in
During OFF time TOFF and before zero-current moment tZCD, multifunctional signal VCS/ZCD is in proportion to drain voltage VD, which is about output voltage VOUT, and over-voltage detector 310 checks if multifunctional signal VCS/ZCD is over high to provide over-voltage protection (OVP). Comparator 320 compares multifunctional signal VCS/ZCD with OVP reference signal VOVP. In case that multifunctional signal VCS/ZCD has been exceeding OVP reference signal VOVP for a predetermined period, timer 322 sends protection signal SOVP to disable pulse-width modulator 312, which in response constantly turns OFF power switch 204 to avoid over-high output voltage VOUT.
Accordingly, PFC controller 202, which is in form of a packaged monolithic chip according to embodiments of the invention, uses only multifunctional pin CS/ZCD to provide multiple protections, such as OVP, OCP, and DSCP, and to detect zero-current moment and signal valleys. PFC controller 202 could have a less pin number, which would make the total cost of PFC circuit 200 more attractive to manufacturers.
While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
| Number | Date | Country | Kind |
|---|---|---|---|
| 109118312 | Jun 2020 | TW | national |
