阅读说明：本技术 电源转换器电路 (Power converter circuit ) 是由 拉塞尔·雅克 戴维·库尔森 于 2017-01-26 设计创作，主要内容包括：一种电源转换器电路(1)和转换交流(AC)电源的相关方法。所述电源转换器电路(1)包括：供电整流电路(2),所述供电整流电路(2)用于整流交流(AC)电源以产生整流的电源；逆变电路(3),所述逆变电路(3)用于接收所述整流的电源,以产生用于负载电路的逆变的电源；以及由所述逆变的电源驱动的电荷泵电路(6),所述电荷泵电路(6)将额外的电荷泵送到所述整流供电电源。(A power converter circuit (1) and associated method of converting Alternating Current (AC) power. The power converter circuit (1) comprises: a power supply rectification circuit (2), the power supply rectification circuit (2) for rectifying an Alternating Current (AC) power supply to produce a rectified power supply; an inverter circuit (3), the inverter circuit (3) being configured to receive the rectified power to generate an inverted power for a load circuit; and a charge pump circuit (6) driven by the inverted power supply, the charge pump circuit (6) pumping additional charge to the rectified power supply.)

1. A power converter circuit comprising:

a power supply rectification circuit for rectifying an alternating current power supply to generate a rectified power supply;

an inverter circuit for receiving the rectified power to generate an inverted power for a load circuit; and

the charge pump circuit is driven by the inverted power supply and pumps additional charge to the rectified power supply and comprises a charge pump diode connected between the power supply rectifying circuit and the inverted circuit, a first capacitor connected across the two ends of a diode of the power supply rectifying circuit or connected with the charge pump diode in parallel and between the power supply rectifying circuit and the inverted circuit, a second capacitor connected between the input end of the power supply rectifying circuit and the inverted power supply and a third capacitor connected between the power supply rectifying circuit and the inverted power supply.

2. The power converter circuit of claim 1, comprising a sensing circuit, wherein an input of the sensing circuit is connected to the inverted power supply and an output of the sensing circuit is connected to the second capacitor and the third capacitor.

3. The power converter circuit of claim 2, wherein the sensing circuit comprises a current sensing device or a voltage sensing device.

4. The power converter circuit of claim 1, comprising a bulk capacitor connected across the inverter circuit.

5. A power converter circuit according to claim 1, including first and second supply lines for receiving the ac supply from an ac supply, the first supply line being connected to the first input of the supply rectifying circuit and the second supply line being connected to the second input of the supply rectifying circuit, a supply capacitor being connected across the first and second supply lines so as to be across the ac supply.

6. The power converter circuit of any of claims 1-5, wherein the inverted power source is connected to a first side of a transformer, the load circuit is connected to a second side of the transformer, and the first side of the transformer is connected to the second capacitor and the third capacitor.

7. The power converter circuit of claim 1, wherein the charge pump circuit comprises only the charge pump diode, the first capacitor, the second capacitor, and the third capacitor.

8. The power converter circuit of claim 1, comprising one or more additional charge pump circuits, each comprising only one charge pump diode and one or two capacitors.

9. The power converter circuit of claim 1, wherein the power supply rectification circuit is a single-phase rectifier bridge having a first input terminal, a second input terminal, a first output terminal, and a second output terminal, the first and second input terminals being connected to the ac power source, the charge pump diode being connected between the first output terminal and the inverter circuit, the first capacitor being connected across one diode of the power supply rectification circuit or in parallel with the charge pump diode and between the first output terminal and the inverter circuit, the second capacitor being connected between the first or second input terminal and the inverted power source, and the third capacitor being connected between the first output terminal and the inverted power source.

10. A method of converting alternating current power, the method comprising:

rectifying the AC power to produce a rectified power;

inverting the rectified power to generate an inverted power for a load circuit; and

pumping additional charge to the rectified power source using the inverted power source.

11. A lighting device comprising the power converter circuit of any one of claims 1 to 9.

12. The lighting device of claim 11, wherein the power converter circuit drives one or more Light Emitting Diodes (LEDs).

Technical Field

The present invention relates to power converter circuits and methods for converting power, and more particularly to circuits and methods for converting Alternating Current (AC) power to rectified Direct Current (DC) power. The present invention is described herein primarily in relation to power converter circuits and methods of converting power suitable for use in power supplies and Light Emitting Diode (LED) drivers, but is not limited to these particular uses.

Background

Without power factor correction, any power connection device that rectifies incoming AC power to produce DC power will have low power factor, high harmonic distortion characteristics that typically exceed the allowable range of the power connection device. Power Supply Units (PSUs) and lighting ballasts designed specifically for high efficiency, cost sensitive consumer applications are typically of the switching type and are typically based on half-bridge or full-bridge topologies. These topologies are particularly suitable for high power, high efficiency applications where the ratio of input voltage to output voltage is relatively limited. Several regulations have been introduced in recent years to restrict the way input current is drawn from an AC power source, including Power Factor (PF), Crest Factor (CF), and Total Harmonic Distortion (THD). Continued pressure to comply with stricter regulations and to reduce manufacturing costs forces a need for innovative approaches in the design of switching power supply controllers.

Various passive switching Power Factor Correction (PFC) circuits have been invented that use the switching power waveform of the power converter to provide a measure of PFC that enables the product to meet statutory regulations at a lower cost, with the disadvantage of high ripple content of the output current through the output load. However, in many applications it is desirable that the current through the output load be substantially constant and have a low ripple content. For example, in the case of LED lighting, a constant output current with low ripple content has the advantage of providing high efficiency and long lifetime, as well as high quality light output without flicker.

Such prior circuits include those disclosed in US5223767A, US6642670B2, US7911463B2, US20090251065a1, WO2008152565a2, WO2010054454a2, WO2010143944a1 and WO9204808a 1. Although these prior circuits achieve a high power factor PF relative to the way the power is drawn from the mains supply, these circuits are generally not able to supply a current to the load that is both regulated and has a low ripple content. WO2015143612a1 discloses a circuit capable of providing regulation of the required current and low ripple content, but which requires a large number of components, resulting in significant additional cost and manufacturing complexity.

It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a practical alternative.

Disclosure of Invention

In a first aspect, the present invention provides a power converter circuit comprising:

a power supply rectifying circuit for rectifying an alternating current power supply to generate a rectified power supply;

the inverter circuit is used for receiving the rectified power supply to generate an inverted power supply for the load circuit; and

the charge pump circuit is driven by an inverted power supply and pumps extra charges to a rectified power supply, and comprises a charge pump diode connected between a power supply rectifying circuit and the inverted circuit, a first capacitor connected between the power supply rectifying circuit and the inverted circuit and bridged at two ends of a diode of the power supply rectifying circuit or connected with the charge pump diode in parallel, a second capacitor connected between the input end of the power supply rectifying circuit and the inverted power supply, and a third capacitor connected between the power supply rectifying circuit and the inverted power supply.

In a second aspect, the present invention provides a method of converting AC power, the method comprising:

rectifying the ac power to produce a rectified power;

inverting the rectified power to generate an inverted power for the load circuit; and

additional charge is pumped to the rectified power supply using the inverted power supply.

In a third aspect, the present invention provides a lighting device comprising the above power converter circuit.

In a fourth aspect, the present invention provides a power converter circuit, comprising:

a power supply rectification circuit for rectifying an AC power supply to generate a rectified power supply;

the inverter circuit is used for receiving the rectified power supply to generate an inverted power supply;

a load rectifying circuit for rectifying the inverted power supply to generate a rectified load power supply for supplying a load current to a load; and

a charge pump circuit driven by the load current, the charge pump circuit pumping additional charge to the rectified power supply.

In a fifth aspect, the present invention provides a method of converting AC power, the method comprising:

rectifying the AC power to produce rectified power;

inverting the rectified power to generate an inverted power;

rectifying the inverted power supply to produce a rectified load power supply for providing a load current to the load; and

additional charge is pumped to the rectified power supply using the load current.

Other features of the various embodiments of the invention are defined in the appended claims. It should be understood that features may be combined in various combinations in various embodiments of the invention.

Throughout the specification (including the claims), the words "comprise", "comprising" and other similar terms are to be construed in an inclusive sense, that is, in a sense including but not limited to "and not exclusive or exhaustive, unless expressly stated otherwise or the context clearly requires otherwise.

Drawings

Preferred embodiments according to the best mode of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

fig. 1 is a schematic diagram of a prior art power converter circuit disclosed in US6642670B 2;

fig. 2 is a schematic diagram of a prior art power converter circuit disclosed in WO2015143612a 1;

FIG. 3 is a schematic diagram of a power converter circuit according to an embodiment of the invention;

FIG. 4 is a schematic diagram of a power converter circuit according to another embodiment of the invention;

FIG. 5 is a schematic diagram of a power converter circuit according to another embodiment of the invention;

FIG. 6 is a schematic diagram of a power converter circuit according to another embodiment of the invention;

FIG. 7 shows typical waveforms for the power converter circuit shown in FIG. 4 or FIG. 5 at optimum operation;

fig. 8 shows typical waveforms for the power converter circuit shown in fig. 4 at non-optimal operation, with a lower mains supply and/or a higher output LED voltage;

fig. 9 shows typical waveforms for the power converter circuit shown in fig. 4 with a higher mains supply and/or a lower output LED voltage when operating non-optimally; and

fig. 10 shows typical waveforms achieved by the first and second charge pump circuits for the power converter circuit shown in fig. 5, showing the PFC effect of the two charge pump circuits alone when operating non-optimally (with high mains and/or low output LED voltage).

Detailed Description

Referring to the drawings, an embodiment of the present invention provides a power converter circuit 1, the power converter circuit 1 including a power supply rectification circuit 2, the power supply rectification circuit 2 rectifying an AC power supply to generate a rectified power supply. The power converter circuit 1 further comprises an inverter circuit 3, the inverter circuit 3 being configured to receive the rectified power to generate an inverted power. The power converter circuit 1 further comprises a load rectifying circuit 4, the load rectifying circuit 4 being arranged to rectify the inverted power supply to produce a rectified load power supply, the rectified load power supply being arranged to provide a load current to a load 5. A charge pump circuit 6 driven by the load current pumps additional charge to the rectified supply. The AC power may be provided by an AC power supply 7, such as a mains supply.

Typically, the waveform of the rectified power supply has peaks and valleys. By using the charge pump circuit 6 to pump additional charge to the rectified power supply, the waveform is smoother and the peaks and troughs are smaller. The resulting waveform is the sum of the rectified power supply waveform before the additional charge is provided and the waveform resulting from the additional charge. In the above power converter circuit 1, almost all of the load current is utilized by the charge pump circuit 6 to provide additional charge. Thus, the power converter circuit 1 achieves a good power factor, a low total harmonic distortion, a tight regulation of the load current or voltage and a low ripple content in the load current or voltage.

The power converter circuit 1 further comprises a sensing circuit 8. An input terminal of the sensing circuit 8 is connected to the load rectifying circuit 4, and an output terminal of the sensing circuit 8 is connected to an input terminal of the charge pump circuit 6. In the present embodiment, the sensing circuit 8 includes a current sensing device. This applies to loads such as LEDs. In particular, the current sensing means may take the form of a resistive element or resistor R1. In other embodiments, the sensing circuit 8 may comprise a voltage sensing device. This applies when the power converter circuit is part of a power supply or power converter that provides a voltage source for a load.

The power converter circuit 1 further comprises a controller 9. The inverter circuit 3 has one or more switches, and the controller controls the switches. In the embodiment shown in the figure, the inverter circuit 3 is a series resonant half bridge inverter with two switches S1 and S2. An input 10 of the controller 9 is connected to the load rectifying circuit 4. The other input 11 of the controller 9 is connected to the output of the sensing circuit 8.

In one embodiment well suited for use with a relatively low voltage mains supply (e.g. 110V) and as best shown in fig. 3, the charge pump circuit 6 comprises a first capacitor C4 connected between the input of the supply rectifier circuit 2 and the output of the sensing circuit 8. The power supply rectifying circuit 2 of the embodiment shown in fig. 3 is a half-bridge rectifying circuit, and the charge pump circuit 6 includes a second capacitor C3 connected across the input and output of the power supply rectifying circuit 2.

In another embodiment, as best shown in fig. 4, the charge pump circuit 6 includes a first capacitor C3 connected across one diode of the supply rectifier circuit 2. The second capacitor C4 is connected between the power supply rectification circuit 2 and the output terminal of the sensing circuit 8.

Preferably, in the embodiment shown in fig. 3 and 4, the charge pump circuit 6 only requires the first capacitor and the second capacitor (C3 and C4). This greatly reduces the complexity and cost of the circuit.

In other embodiments, the power converter circuit 1 includes two or more of the charge pump circuits 6. For example, fig. 5 shows a power converter circuit 1 having two charge pump circuits 6. A first of these charge pump circuits 6 comprises a first capacitor C3 connected across the diode D2 of the supply rectifier circuit 2 and a second capacitor C4 connected between the supply rectifier circuit 2 and the output of the sense circuit 8. The second charge pump circuit 6 includes a charge pump diode D5 connected between the power supply rectifying circuit 2 and the inverter circuit 3, a third capacitor C6 connected in parallel with the charge pump diode D5 and between the power supply rectifying circuit 2 and the inverter circuit 3, and a fourth capacitor C7 connected between the power supply rectifying circuit 2 and the output terminal of the sensing circuit 8.

The first charge pump circuit 6 includes C3 and C4, and the first charge pump circuit 6 operates by pumping charge from an AC power supply input to the large-capacity capacitor C5. The second charge pump circuit 6 includes C6, C7, and D5, and the second charge pump circuit 6 similarly operates by pumping charge from the AC power input to the bulk capacitor C5. In the two charge pump circuits 6, C6 corresponds to C3, and C7 corresponds to C4. Having more charge pump circuits 6 provides more improved performance, such as better Power Factor (PF), lower Total Harmonic Distortion (THD), tighter load current or voltage regulation, and lower ripple content in the load current or voltage.

As indicated above, the power converter circuit 1 may comprise one or more additional charge pump circuits 6, each comprising a charge pump diode and one or more additional capacitors, wherein the charge pump diode is connected to another diode. The further diode may be a diode of the supply rectifier circuit 2 or a charge pump diode of another additional charge pump circuit. In a particularly preferred embodiment, only one charge pump diode and one or two charge pump capacitors are required per additional charge pump circuit 6. For example, the first charge pump circuit 6 of the embodiment shown in fig. 5 includes only two capacitors C3 and C4, and the second charge pump circuit 6 of the same embodiment includes only two capacitors C6 and C7, and one charge pump diode D5. This greatly reduces the complexity and cost of the circuit.

As can be appreciated from the foregoing, embodiments of the present invention provide a power converter circuit 1, the power converter circuit 1 including a power supply rectification circuit 2 for rectifying an AC power supply to produce a rectified power supply. The power converter circuit 1 further comprises an inverter circuit 3, the inverter circuit 3 being configured to receive the rectified power to generate an inverted power for the load circuit 4. A charge pump circuit 6 driven by the inverted power supply pumps additional charge to the rectified power supply. The charge pump circuit 6 includes a charge pump diode D5 connected between the power supply rectification circuit 2 and the inverter circuit 3. A first capacitor C3 or C6 is connected across the diode D2 of the power supply rectification circuit 2 or in parallel with the charge pump diode D5 and between the power supply rectification circuit 2 and the inverter circuit 3. The second capacitor C4 is connected between the input terminal of the power supply rectifying circuit 2 and the inverted power supply, and the third capacitor C7 is connected between the power supply rectifying circuit 2 and the inverted power supply. In one embodiment, the power supply rectification circuit 2 is a single-phase rectifier bridge having a first input terminal, a second input terminal, a first output terminal, and a second output terminal, the first input terminal and the second input terminal being connected to an AC power source. The charge pump diode D5 is connected between the first output terminal and the inverter circuit 3, and the first capacitor C3 or C6 is connected across one diode D2 of the power supply rectification circuit 2 or in parallel with the charge pump diode D5 and between the first output terminal and the inverter circuit 3. The second capacitor C4 is connected between the first or second input terminal and the inverted power source, and the third capacitor C7 is connected between the first output terminal and the inverted power source.

As best shown in fig. 6, the power converter circuit 1 may include one or more switching charge pump circuits 13. Each such switched charge pump circuit 13 comprises a charge pump capacitor C10 connected between the power supply rectification circuit 2 and the output of the sensing circuit 8, and a charge pump switch S3 connected in parallel with the charge pump capacitor C10. The charge pump switch S3 forms part of a series combination with another charge pump capacitor C11, which combination is connected in parallel with the charge pump capacitor C10. The state of the charge pump switch S3 is responsive to the sensed circuit parameter. The sensed circuit parameter may be a DC bulk supply voltage. Typically, the controller 9 has an output 12 connected to the charge pump switch S3 to control the charge pump switch S3 based on the sensed circuit parameter.

As described above, the power converter circuit 1 includes the large-capacity capacitor C5. The bulk capacitor C5 may be connected across the inverter circuit 3. As shown in fig. 3, there may also be two bulk capacitors C5 and C12 connected across the inverter circuit 3.

The power converter circuit 1 includes a first power supply line L and a second power supply line N to receive AC power from the AC power supply 7. The first supply line L is connected to a first input of the power supply rectification circuit 2, and the second supply line N is connected to a second input of the power supply rectification circuit 2. A supply capacitor C1 is connected across the first and second power lines and thus across the AC supply 7. To reduce EMI, a power supply inductor L1 may be connected in series with the first power supply line L, and the power supply inductor L1 is located between the power supply capacitor C1 and the first input terminal of the power supply rectification circuit 2. A second supply capacitor C2 may also be connected across the first and second power supply lines, across the AC supply 7, and between the supply inductor L1 and the supply rectifier circuit 2.

As indicated above, the power supply rectifier circuit 2 may take the form of a half-bridge rectifier circuit as shown in fig. 3, said power supply rectifier circuit 2 having diodes D1 and D3, or a full-bridge rectifier circuit as shown in fig. 4, 5 and 6, having diodes D1, D2, D3 and D4.

The inverter circuit 3 includes two switches S1 and S2 connected in series. The inverter circuit 3 further comprises an inverter inductor L2, the inverter inductor L2 having an inverter inductor input connected between the two switches.

In one embodiment, as best shown in fig. 3, the inverter inductor L2 has an inverter inductor output connected to the load rectification circuit 4. The load rectifying circuit in this embodiment includes a full bridge rectifier having four diodes D20, D21, D22 and D23.

In other embodiments, as best shown in fig. 4, 5 and 6, the inverter inductor L2 has an inverter inductor output connected to a first side of the transformer T1, while the load rectification circuit 4 is connected with a second side of the transformer T1. Thus, the load is isolated from the AC power supply 7. The load rectifying circuit 4 in these embodiments includes two diodes D20 and D21.

Those skilled in the art will appreciate that there are different circuit variations within the scope of the present invention. The circuit components shown in the embodiments may be placed in a different arrangement or order while still falling within the scope of the invention and providing the functionality described by the circuits as initially arranged or ordered in the described embodiments. For example, in the embodiments shown in fig. 4, 5, and 6, the inverter inductor L2, the transformer T1, and the resistor R1 are connected in series. It will be appreciated by those skilled in the art that these components may be freely interchanged while still providing the same functionality as the components provided before the interchange and, thus, still falling within the scope of the present invention.

Accordingly, some preferred embodiments of the present invention generally provide a power converter circuit having a series resonant half-bridge inverter, one or more passive charge pump circuits, and a controller that corrects the PF and minimizes harmonic distortion of the input current.

The resonant tank is formed by a series combination of an inductor and a capacitor in a passive charge pump circuit. The Q factor of the resonant tank determines in part the switching frequency variation that the controller must utilize to achieve the necessary PF and harmonic distortion levels over the required AC power range (e.g., mains input and output loads).

In one embodiment, the passive charge pump circuit is comprised of two diodes and at least one capacitor. A high proportion, if not almost all, of the current flowing through the resonant tank of the series resonant inverter is coupled into the passive charge pump circuit through a capacitor, with the current flowing through one of the two diodes depending on the polarity of the current itself at any instant. During one half cycle of the inverter, one diode conducts, so that energy is transferred from the mains supply to the resonant tank. During the second half-cycle, the other diode conducts, causing energy to be transferred from the resonant tank to the bulk capacitor. An optional second capacitor may be used to modify the conduction time of the two diodes so that the charge pumping action is dependent on the frequency and potential difference across the two diodes.

A power filter comprising reactive elements (L1, C1 and C2) is coupled between the power supply terminals (L, N) and the bridge supply rectifier circuit 2 to suppress unwanted emissions related to the inverter switching frequency.

In a preferred topology of the invention, the half-bridge circuit drives a series combination of a resonant inductor, an output load and a passive charge pump circuit. Thus, the controller can accurately regulate the output current by detecting and regulating the current through the resonant tank. Thus, there is no need to remotely sense using a device such as an optocoupler, which is particularly advantageous when driving an isolated load. In addition, no additional resonant current loop is required to provide the charge pumping function, since the load current itself drives the passive charge pump circuit, thereby achieving the advantages of the present invention with minimal power consumption and complexity.

For example, for a typical LED lighting application with a single wire input and output voltage range varying up to 30% from nominal, THE present invention can achieve PF >0.95 with only one passive charge pump circuit, and harmonic emission in accordance with THE than < 20%. In this case, the burden of adding PF correction and low harmonic emission is only the cost of two inexpensive passive elements (C3 and C4).

The present invention may also employ multiple passive charge pump circuits that work together to achieve good PF and low harmonic distortion over a wider range of input and output voltages than can be achieved with a single passive charge pump stage. Comparing the embodiments shown in fig. 4 and 5, a second charge pump stage may be provided by adding only two capacitors and one diode (C6, C7 and D5). For example, a typical constant current LED lighting application needs to operate in THE two-wire input (220V/240V) and 50-100% output voltage range, if two passive charge pump stages are employed, PF >0.95 can be achieved, and harmonic emission is in accordance with THE than < 20%. More charge pump stages can be added in the same manner to achieve better PF and harmonic emission.

Considering the above diagram more specifically, fig. 1 shows a half-bridge ballast for a fluorescent lamp that employs passive power factor correction to achieve good PF and harmonic emissions. Fig. 3 shows an embodiment of a half-bridge converter according to the invention. Comparing the circuits shown in fig. 1 and 3, it can be seen that the current flowing into the charge pump of the first converter is significantly different from the current in the second converter. In fig. 1, the current flowing into the charge pump a is the sum of the lamp current and the current in the parallel resonant capacitor B that changes due to the presence of the parallel capacitor C. In fig. 3, the current flowing into the charge pump is substantially the load current obtained from the load current sensor 8. Thus, the controller 9 in fig. 3 can achieve simultaneous fine adjustment of the load current and the charge pump current, thereby optimizing PF and harmonic emission.

Fig. 2 shows a typical isolated half-bridge driver circuit according to WO2015143612a1, while fig. 4 shows an embodiment of the invention. Both circuits have a single charge pump stage, but the present invention achieves similar performance by reducing one element D5. This greatly reduces the effort, time and cost of manufacture, especially when these circuits are produced on a large scale. Having fewer components, even a reduction in one component, reduces circuit complexity, which increases circuit robustness and reliability.

Referring to fig. 4, the mains voltage source (L, N) is connected to a low pass input filter comprising C1, L1, C2. Typically, the low-pass input frequency bandwidth will be lower than the switching frequency of the power converter, but higher than the mains voltage supply frequency. The output of the filter is connected to the input of a full wave rectifier bridge (D1, D2, D3 and D4). Capacitors C3, C4 are connected to the junction of D2, D4 to form a passive charge pump circuit that pumps current from the input filter circuit through D2 and D4 to the positive terminal of a DC bulk capacitor C5. The controller 9(U1) alternately drives the half-bridge switches S1 and S2 to generate an alternating voltage at the first connection of the resonant inductor L2, while the second connection of the resonant inductor L2 is coupled to the first primary connection of the isolation transformer T1. The second primary connection of T1 is connected to the first connection of a current sensing device R1, the second connection of which current sensing device R1 is connected to the first connection of a charge pump circuit 6 comprising C3 and C4. A second connection of the charge pump circuit 6 (comprising C3 and C4) is connected to one output connection of the bridge rectifier 2(D1, D2, D3, D4), and a third connection of the charge pump circuit 6(C3 and C4) is connected to a second output connection of the bridge rectifier 2(D1, D2, D3, D4). The first and second secondary connections of the isolation transformer T1 are connected to first and second inputs of the output rectifier 4, including D20 and D21. The output of the output rectifier 4 is connected to a first connection of a load 5, a second connection of said load 5 being connected to a third secondary connection of an isolation transformer T1.

It can be seen that the current passing through the current sensor 8 is a load current which is transformed by the transformer T1 and rectified by the output diodes D20 and D21, and thus a high-precision DC current with a very low ripple content can be realized.

Fig. 5 shows a possible extension of the invention where the application requirements are for a wider voltage range on the mains input or a larger voltage or current range on the output load. Here, by adding the second charge pump circuit 6 including the capacitors C6 and C7 and the diode D5, the limitation of the power converter circuit shown in fig. 4 can be alleviated. The second charge pump circuit 6 will preferably use a different capacitance value than in the first charge pump circuit 6 and will therefore operate with different characteristics than the first charge pump stage 6.

Fig. 7 shows the current and voltage waveforms when the circuit of fig. 4 operates optimally. The same current through the load also flows through the passive charge pump circuit 6 (formed by C3 and C4 in combination with D2 and D4), which generates a voltage across the bulk capacitor C5. Here, the voltage developed across the charge pump capacitor C3 is large enough to force the diodes D2 and D4 to conduct for a portion of each switching cycle throughout the entire cycle of the entire line supply waveform. As the line voltage approaches the zero crossing, conduction through D2 and D4 is almost, but not completely, cut off, so the current drawn from the power supply is minimal. Therefore, there is almost no charge pumping at this time. However, near the peak of the line voltage, conduction of D2 and D4 is maximum, about 50%, thereby maximizing the current drawn from the line power supply.

Fig. 8 shows the current and voltage waveforms that occur in the case of a drop in the input voltage of the circuit of fig. 4 (assuming the controller maintains the output voltage and current at substantially the same level). The reduction in the input voltage results in a reduction in the average voltage and an increase in the ripple content on the DC bulk capacitor C5. The control circuit reduces the switching frequency to maintain load current regulation so that the current through diodes D2 and D4 increases, which partially compensates for the bulk supply voltage. However, the reduction of the bulk supply voltage and the increase of the ripple content means that when the mains voltage is at a peak, the bulk voltage drops below the rectified mains voltage. At this time, one arm (D3 and D1, or D4 and D2) of the bridge rectifier 2 is almost on, superimposing a sharp pulse on the current waveform. The mains current waveform is now rich in harmonics and is therefore unlikely to meet the legal requirements of the harmonic emission standard.

Fig. 9 shows the opposite set of voltage and current waveforms that occur as the input voltage increases (again assuming that the controller maintains the output voltage and current at substantially the same level). As in the former case, the distorted line current waveform is rich in harmonics and therefore unlikely to meet the harmonic emission standard.

The bad current waveform of fig. 9 can be improved by reducing the capacitance value of C3, thereby increasing more HT voltage, but this forces the voltage rating of HT capacitor C5 to increase, thereby increasing cost. A better alternative is shown in fig. 10, where the distorted current waveform of fig. 9 can be improved by adding a second charge pump circuit (C6, C7, and D5) to the converter circuit, as shown in fig. 5. Thus, the use of two or more passive charge pump circuits may improve the PF and reduce harmonic distortion under these conditions.

Fig. 6 shows another extension of the invention, where the application requirement is for a wider voltage range on the mains input or output load. In this case one or more charge pump stages may be added, comprising one or more active switches in series with one or more charge pump capacitors, to allow the controller 9 to modify the characteristics of the charge pump. Referring to fig. 6, the switching charge pump circuit 13 includes capacitors C9, C10, and C11 working together with diodes D2 and D4 of the power supply rectification circuit 2, and a switch S3. The switch charge pump circuit 13 has a first connection to the return terminal of the current sensor 8, a second connection to the input of the power rectifier 2, a third connection to the DC bulk capacitor C5, and an input connection of the switch S3 to the controller 9. The switch S3 is controlled by a signal from the output connection 12 of the controller 9 in response to a circuit parameter such as the DC bulk supply voltage, the input voltage, the output voltage, the load current, the switching frequency or some combination thereof. The amount of additional charge pumped is determined by the switch position of S3 and the capacitance values of C9, C10 and C11, with more charge when switch S3 is open. Preferably, when the controller 9 detects that the bulk supply voltage has exceeded a predetermined value, the switch S3 will close, thereby protecting the bulk capacitor C5 from excessive voltage. Alternatively, switch S3 may be switched synchronously with inverter circuit 3 at a duty cycle that is responsive to the sensed circuit parameter. Optionally, capacitors may be added or omitted in the switched charge pump circuit 13 to modify the charge pumping characteristics as desired. Further, a switch may be inserted in series with any capacitor, depending on the desired switched charge pumping characteristics.

In another aspect, the invention also provides a method of converting AC power. In a preferred embodiment, the method includes rectifying the AC power source to produce a rectified power source, inverting the rectified power source to produce an inverted power source, rectifying the inverted power source to produce a rectified load power source for providing a load current to the load, and pumping additional charge to the rectified power source using the load current.

Additional features of preferred embodiments of the method have been described above or are apparent from the description above.

The invention achieves good power factor, low total harmonic distortion, tight regulation of load current or voltage, and low ripple content in the load current or voltage. Furthermore, these advantages are all provided at the lowest cost, since only passive components are used.

The present invention provides power converter circuits and methods for converting a power source using passive charge pumping techniques to provide a regulated or substantially constant DC current or voltage to a load, achieving an input current with a high power factor, an output current or voltage with low ripple content and low harmonic distortion. More particularly, the present invention is applicable to power supplies such as switching power converters (SMPCs), including switching power supplies (SMPS), inverters, lighting ballasts, and flicker-free Light Emitting Diode (LED) drivers. In particular, the present invention preferably provides an apparatus and method for controlling the power factor of an AC-DC power converter. The invention is particularly applicable to resonant switching power converters.

It is to be understood that the above-described embodiments are merely exemplary embodiments for illustrating the principles of the present invention and that the present invention is not limited thereto. Various changes and modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the invention, and such changes and modifications are also encompassed within the scope of the invention. Thus, although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms. Those skilled in the art will also appreciate that the features of the various examples described may be combined in other combinations. In particular, there are many possible arrangements of the above described circuit arrangement which use the same passive approach to achieving passive power factor correction, and which will be apparent to those skilled in the art.