CN111987897A - High-voltage starting circuit for PFC topology, PFC circuit and AC/DC converter - Google Patents

Abstract

The present disclosure provides a high voltage start-up circuit for a power factor corrector circuit, a power factor corrector circuit having the high voltage start-up circuit, and an ac/dc converter having the power factor corrector circuit. The high-voltage starting circuit comprises: a switching transistor connected in series between two low-frequency switching transistors in a low-frequency arm of the power factor corrector circuit, wherein a drain of the switching transistor is connected to the alternating current input terminal, a gate of the switching transistor is connected to the alternating current input terminal via a resistor and to ground via a zener diode, and a source of the switching transistor is connected to ground via a starting capacitor.

Description

High-voltage starting circuit for PFC topology, PFC circuit and AC/DC converter

Technical Field

The present disclosure relates to the field of power supplies, and more particularly, to a high voltage start-up circuit for a Power Factor Corrector (PFC) topology. In addition, the disclosure also relates to a PFC circuit with the high-voltage starting circuit and an alternating current/direct current (AC/DC) converter using the PFC circuit.

Background

A large number of electronic devices require the use of an AC/DC converter to convert low frequency mains AC power to DC power that the electronic devices can use directly. The PFC topology has advantages of a small number of components, low common mode noise, high conversion efficiency, and the like, and thus is widely used in AC/DC converters.

However, existing high voltage start-up circuits for AC/DC converters are not suitable for AC/DC converters using PFC topologies due to their size and cost, and there is a need for a high voltage start-up circuit suitable for use with PFC topologies.

Disclosure of Invention

The following presents a simplified summary of the disclosure in order to provide a basic understanding of some aspects of the disclosure. However, it should be understood that this summary is not an exhaustive overview of the disclosure. It is not intended to identify key or critical elements of the disclosure or to delineate the scope of the disclosure. Its sole purpose is to present some concepts of the disclosure in a simplified form as a prelude to the more detailed description that is presented later.

In view of the above problems, it is an object of at least one embodiment of the present disclosure to provide a small-sized, low-cost high-voltage start-up circuit suitable for an AC/DC converter using a PFC topology.

According to one aspect of the present disclosure, there is provided a high voltage start-up circuit for a Power Factor Corrector (PFC) circuit, comprising: and a switching transistor connected in series between two low-frequency switching transistors in a low-frequency arm of the power factor corrector circuit, wherein a drain of the switching transistor is connected to the alternating current input terminal, a gate of the switching transistor is connected to the alternating current input terminal via a resistor and to ground via a zener diode, and a source of the switching transistor is connected to ground via a starting capacitor.

According to another aspect of the present disclosure, there is provided a PFC circuit including the high voltage start-up circuit according to the above aspect of the present disclosure.

According to another aspect of the present disclosure, there is provided an alternating current/direct current converter including a PFC circuit according to the above aspect of the present disclosure, a direct current/direct current (DC/DC) circuit; and a controller for controlling the PFC circuit and the DC/DC circuit.

Additional aspects of the disclosed embodiments are set forth in the description section that follows, wherein the detailed description is presented to fully disclose preferred embodiments of the disclosed embodiments without imposing limitations thereon.

Drawings

The above and other objects, features and advantages of the present disclosure will be more readily understood by reference to the following description of embodiments of the present disclosure taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of a typical two-stage AC/DC converter;

fig. 2 is a circuit diagram of a typical totem-pole PFC topology circuit;

FIG. 3 is a circuit diagram of a typical high voltage start-up circuit;

FIGS. 4A and 4B are schematic diagrams of the current path of the high voltage start-up circuit shown in FIG. 3;

FIG. 5 is a schematic circuit diagram of an AC/DC converter 500 according to an embodiment of the present disclosure; and

fig. 6 is a waveform diagram of an AC input voltage, a driving voltage of a switching transistor, and a direct current operating voltage in the AC/DC converter of fig. 5.

Detailed Description

Hereinafter, some embodiments of the present disclosure will be described in detail with reference to the accompanying illustrative drawings. When elements of the drawings are denoted by reference numerals, the same elements will be denoted by the same reference numerals although the same elements are shown in different drawings. Further, in the following description of the present disclosure, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure unclear.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms are intended to include the plural forms as well, unless the context indicates otherwise. It will be further understood that the terms "comprises," "comprising," and "having," when used in this specification, are intended to specify the presence of stated features, entities, operations, and/or components, but do not preclude the presence or addition of one or more other features, entities, operations, and/or components.

Unless otherwise defined, all terms used herein including technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which the inventive concept belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. The present disclosure may be practiced without some or all of these specific details. In other instances, to avoid obscuring the disclosure with unnecessary detail, only components that are germane to the aspects in accordance with the disclosure are shown in the drawings, while other details that are not germane to the disclosure are omitted.

A core idea of the technology of the present disclosure is to provide a high-voltage start-up circuit that can be applied to an AC/DC converter using a PFC topology.

Hereinafter, preferred embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings.

Figure 1 shows. As shown in fig. 1, the AC/DC converter includes a PFC circuit stage, a DC/DC circuit stage, and a controller. The PFC circuit stage is used for receiving alternating-current input voltage, executing power factor correction, enabling input current to have the same frequency and phase as the input voltage, and therefore restraining harmonic waves to avoid polluting a power grid and outputting output voltage with power frequency ripples.

The DC/DC circuit stage is used for converting the power output by the PFC circuit stage into direct current power required by electronic equipment, and meanwhile, electric isolation is achieved. For the DC/DC circuit stage, it may be implemented in the form of an LLC transformer.

The controller is for providing control signals to the PFC circuit stage and the DC/DC circuit stage. In some embodiments, the controller is configured to provide gate drive signals to switching transistors in the PFC and DC/DC circuit stages.

As an example, fig. 2 shows a typical totem-pole PFC topology circuit 200.

As shown in fig. 2, the high frequency switching transistors Q1 and Q2 constitute a high frequency leg operating in a high frequency PWM mode, and the low frequency switching transistors Q3 and Q4 constitute a low frequency leg operating at a power frequency switching cycle. In fig. 2, L denotes a positive power terminal of an input ac voltage, which is connected to a first circuit node in the middle of the high-frequency switching transistors Q1 and Q2 of the high-frequency arm; n denotes a negative power terminal of an input ac voltage, which is connected to a second circuit node between the high-frequency switching transistors Q3 and Q4 of the high-frequency arm; and C1 denotes a load capacitor.

In some embodiments of the present disclosure, gallium nitride (GaN) High Electron Mobility Transistors (HEMTs) may be used to implement high frequency switching transistors Q1 and Q2 because HEMTs have fast reverse recovery capability. In addition, silicon Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) with low on-resistance may be used to implement the low frequency switching transistors Q3 and Q4.

During operation of the circuit shown in fig. 2, the MOSFET switch Q4 is conducting and the MOSFET switch Q3 is off during the positive half-cycles of the input voltage, and the MOSFET switch Q3 is conducting and the MOSFET switch Q4 is off during the negative half-cycles of the input voltage.

In both the positive and negative half cycles of the input voltage of fig. 2, the primary current path contains only one high frequency switching transistor (Q1 or Q2) and one low frequency switching transistor (Q4 or Q3) to power the load.

In order to prevent the bridge arm from going through, it is necessary to set a dead time between the two high frequency switching transistors Q1 and Q2 of the high frequency bridge arm. In addition, the totem-pole PFC topology has the problem of current spikes near the ac voltage zero crossing. Therefore, the turn-on timing of each of the switching tubes Q1-Q4 is usually controlled at a specific timing using an external controller. As shown in fig. 2, the gates of the respective switching transistors Q1-Q4 are connected to a pulse signal source provided by a controller, and thus the switching of the respective switching transistors Q1-Q4 is controlled by the pulse signal source provided by the controller.

Since totem-pole PFC topologies are known to those skilled in the art, the basic principles of the totem-pole PFC topology will not be described in greater detail here for the sake of brevity.

The existing AC/DC converter usually includes a high voltage start circuit, which is used to start the controller when the controller is powered on, drive the transformer in the DC/DC circuit stage to convert the voltage to realize the normal operation of the AC/DC converter, and after the start is finished, the controller is powered by the auxiliary winding in the DC/DC circuit stage.

Fig. 3 shows a typical high voltage start-up circuit 300. As shown in fig. 3, the high voltage start circuit 300 includes a resistor R1, a zener diode D1, a start capacitor C3, and a switching transistor Q5. In some embodiments, the switching transistor Q5 may be a MOSFET.

Upon power-up of the ac input voltage, the input current charges the start-up capacitor C3 and the input capacitance of the switching transistor Q5. At this time, the switching transistor Q5 is turned off, and the current path is as shown in fig. 4A.

When the input capacitance of the switching transistor Q5 is charged to the turn-on threshold voltage Vgsth5 of the switching transistor Q5, the switching transistor Q5 is turned on. At this time, the current path is as shown in fig. 4B, the input current directly charges the starting capacitor C3 through the switching transistor Q5 which is turned on.

The maximum charging voltage of the start-up capacitor C3 is VD1-Vgsth5, where VD1 is the regulated voltage of the zener diode D1. The DC operating voltage Vcc of the controller for controlling the PFC circuit stage and the DC/DC circuit stage is equal to VD1-Vgsth 5. For example, Vcc may be 12 Vdc. At this point the start-up is complete and Vcc is supplied during subsequent operation via the auxiliary winding of the DC/DC circuit stage.

The high voltage startup circuit 300 may be integrated with the PFC topology circuit 200.

As described above, the controller included in the AC/DC converter is used to provide control signals to the PFC circuit stage and the DC/DC circuit stage. The controller may need to draw a large current, for example about 100mA, at start-up. If a high voltage start-up circuit is used as shown in fig. 3, an additional high voltage needs to be applied to the switching transistor Q5 to provide enough current to drive the controller, for example, about 600V. This may cause heating problems for the overall system. Furthermore, providing such a starting current necessarily requires the use of a larger capacitor. These all contribute to a negative impact on the size and cost of the overall system.

The high-voltage start-up circuit according to the embodiment of the present disclosure can be applied to an AC/DC converter using a PFC topology while not requiring high voltage and a complicated circuit configuration.

Fig. 5 shows a schematic circuit diagram of an AC/DC converter 500 according to an embodiment of the present disclosure.

As shown in fig. 5, the PFC circuit stage is substantially the same as the PFC circuit stage shown in fig. 2 except that a switching transistor Q6 is connected in series between the low-frequency switching transistors Q3 and Q4 of the low-frequency arm of fig. 2 as a high-voltage start-up transistor. Further, after startup, the switching transistor Q6 participates in power output as a low frequency switching transistor, at which time the switching transistor Q4 also functions as a signal transistor.

As shown in fig. 5, the high voltage start-up transistor Q6 may be implemented by a MOSFET. The drain of the high voltage enable transistor Q6 is connected to the source of the low frequency switch transistor Q3 and to the second circuit node. The gate of the high voltage enable transistor Q6 is connected to the second circuit node through a resistor R2 and to ground through a zener diode D1. The source of the high voltage enable transistor Q6 is connected to the drain of the low frequency switch transistor Q4. Further, the source of the high voltage start transistor Q6 is connected to a start capacitor C3 and a start resistor R3 via an ideal diode D2. The zener diode D1 and the starting capacitor C3 here may be the same as the zener diode D1 and the starting capacitor C3 in fig. 3.

The high-voltage start transistor Q6, the resistor R2, the zener diode D1, the ideal diode D2, the start capacitor C3, and the start resistor R3 constitute a high-voltage start circuit.

The circuit portion to the right of load capacitor C1 in fig. 5 constitutes a DC/DC circuit stage. In the embodiment shown in fig. 5, the DC/DC circuit stage is implemented by an LLC transformer. In view of the fact that LLC transformers are known to a person skilled in the art, the basic principles of LLC transformers are not described in more detail here for the sake of brevity.

As shown in fig. 5, at power-up of the AC/DC converter 500, all switching transistors in the circuit are in an off state. Thus, the input current charges the starting capacitor C3 through the resistor R2, the input capacitance of the switching transistor Q6, and the ideal diode D2.

Similar to the process shown in fig. 4A and 4B, the switching transistor Q6 is turned on when the input capacitance of the switching transistor Q6 is charged to the turn-on threshold voltage Vgsth6 of the switching transistor Q6. At this time, the input current directly charges the starting capacitor C3 through the turned-on switching transistor Q6.

The maximum charging voltage of the start-up capacitor C3 is VD1-Vgsth6, where VD1 is the regulated voltage of the zener diode D1. The DC operating voltage Vcc of the controller for controlling the PFC circuit stage and the DC/DC circuit stage is equal to VD1-Vgsth 6. At this point the start-up is over and Vcc is supplied during subsequent operation by the auxiliary winding P2 of the DC/DC circuit stage, as shown in fig. 5.

According to an embodiment of the present disclosure, the DC/DC circuit stage may comprise an LLC transformer. As shown in fig. 5, the DC/DC circuit stage may include switching transistors Q7, Q8, capacitors C2, C4, C5, C6, ideal diodes D3, D4, D5, inductor L1, transformer TX1 including windings P1, P2, S1, S2.

According to the embodiment of the present disclosure, since a low-voltage small-sized transistor Q6 can be used for high-voltage start-up, a current sufficient to start up the controller can be supplied, avoiding the problems in the prior art described above.

Fig. 6 shows waveforms of the AC input voltage, the driving voltages of the switching transistors Q4, Q6, and the direct current operating voltage Vcc in the AC/DC converter 500, where the abscissa is time in milliseconds and the ordinate is voltage in volts.

According to the embodiment of the disclosure, a high-voltage starting circuit can be integrated into a PFC topological structure, the high-voltage starting circuit has the advantages of small starting voltage and small circuit size, and the manufacturing cost of an AC/DC converter using the PFC topological structure can be greatly reduced.

Although the high voltage start-up circuit according to embodiments of the present disclosure is described above in a totem-pole PFC topology, one skilled in the art will recognize that the high voltage start-up circuit according to embodiments of the present disclosure may be equally applied to other PFC topologies, such as a pseudo-totem-pole PFC topology.

While the disclosure has been disclosed by the description of the specific embodiments thereof, it will be appreciated that those skilled in the art will be able to devise various modifications, improvements, or equivalents of the disclosure within the spirit and scope of the appended claims. Such modifications, improvements and equivalents are also intended to be included within the scope of the present disclosure.

Claims (9)

1. A high voltage startup circuit for a power factor corrector circuit, comprising:

a switching transistor connected in series between two low-frequency switching transistors in a low-frequency leg of the power factor corrector circuit,

wherein a drain of the switching transistor is connected to the alternating current input terminal, a gate of the switching transistor is connected to the alternating current input terminal via a resistor and to ground via a zener diode, and a source of the switching transistor is connected to ground via a start capacitor.

2. The high voltage startup circuit of claim 1 wherein the power factor corrector circuit is a totem pole power factor corrector circuit.

3. The high voltage startup circuit of claim 1 wherein the power factor corrector circuit is a pseudo-totem pole power factor corrector circuit.

4. The high voltage startup circuit of claim 1 wherein the high frequency leg of the power factor corrector circuit comprises two gallium nitride high electron mobility transistors connected in series.

5. The high voltage startup circuit of claim 1 wherein the switching transistor is a metal oxide semiconductor field effect transistor.

6. A power factor corrector circuit comprising a high voltage start-up circuit as claimed in any one of claims 1 to 5.

7. An ac/dc converter comprising:

the power factor corrector circuit of claim 6;

a DC/DC circuit; and

a controller that controls the power factor corrector circuit and the DC/DC circuit.

8. The ac/dc converter of claim 7, wherein the dc/dc circuit comprises an LLC transformer.

9. The ac/dc converter of claim 7 wherein the controller comprises a digital signal processor.

Images