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

Abstract

The present disclosure provides a high-voltage startup circuit for a power factor corrector circuit, a power factor corrector circuit having the high-voltage startup circuit, and an AC/DC converter having the power factor corrector circuit. The high-voltage startup circuit includes: a switching transistor, which is connected in series between two low-frequency switching transistors in a low-frequency bridge arm of the power factor corrector circuit, wherein the drain of the switching transistor is connected to an AC input terminal, the gate of the switching transistor is connected to the AC input terminal via a resistor and to ground via a voltage regulator diode, and the source of the switching transistor is connected to ground via a startup capacitor.

Description

High Voltage Startup Circuits, PFC Circuits and AC/DC Converters for PFC Topologies

technical field

The present disclosure relates to the technical field of power supplies, and more particularly, to high voltage startup circuits for power factor corrector (PFC) topologies. In addition, the present disclosure also relates to a PFC circuit having the high voltage start-up circuit and an alternating current/direct current (AC/DC) converter using the PFC circuit.

Background technique

A large number of electronic devices need to use AC/DC converters to convert low-frequency mains AC power into DC power that can be directly used by electronic devices. PFC topology is widely used in AC/DC converters due to its advantages of small number of components, low common-mode noise, and high conversion efficiency.

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, so there is a need for a high voltage suitable for use with PFC topologies start the circuit.

SUMMARY OF THE INVENTION

The following presents a brief summary of the disclosure in order to provide a basic understanding of certain aspects of the disclosure. It should be understood, however, that this summary is not an exhaustive overview of the present disclosure. It is not intended to identify key or critical parts of the disclosure nor to limit the scope of the disclosure. Its sole purpose is to present some concepts related to the disclosure in a simplified form as a prelude to the more detailed description that is presented later.

In view of the above problems, an object of at least one embodiment of the present disclosure is 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: a switching transistor, two low frequency switches connected in series in a low frequency bridge arm of the power factor corrector circuit between transistors, where the drain of the switching transistor is connected to the AC input terminal, the gate of the switching transistor is connected to the AC input terminal via a resistor and is connected to ground via a Zener diode, and the source of the switching transistor is connected to ground via a startup capacitor .

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

According to another aspect of the present disclosure, there is provided an AC/DC converter comprising the PFC circuit according to the above-mentioned aspects of the present disclosure, a direct current/direct current (DC/DC) circuit; and a control for controlling the PFC circuit and the DC/DC circuit controller.

Other aspects of the embodiments of the present disclosure are set forth in the following specification section, wherein the preferred embodiments are described in detail to fully disclose the embodiments of the present disclosure without imposing limitations thereto.

Description of drawings

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

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

Figure 2 is a circuit diagram of a typical totem pole PFC topology circuit;

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

4A and 4B are schematic diagrams of the current paths 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 the AC input voltage, the driving voltage of the switching transistor and the DC operating voltage in the AC/DC converter of FIG. 5 .

Detailed ways

Hereinafter, some embodiments of the present disclosure will be described in detail with reference to the accompanying illustrative figures. Where reference numerals are used to designate elements of the figures, the same elements will be denoted by the same reference numerals even though they are shown in different figures. Also, in the following description of the present disclosure, a detailed description of known functions and configurations incorporated herein will be omitted where 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 limit the present disclosure. As used herein, the singular forms are intended to include the plural forms as well, unless the context dictates otherwise. It will also be understood that the terms "comprising", "comprising" and "having" used in the specification are intended to specify the presence of stated features, entities, operations and/or components, but not to exclude one or more The presence or addition of other features, entities, operations and/or components.

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

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, in order to avoid obscuring the disclosure with unnecessary detail, only components closely related to the solutions according to the present disclosure are shown in the drawings, while other details less relevant to the present disclosure are omitted.

The core idea of the technology of the present disclosure is to provide a high voltage start-up circuit that can be adapted 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 Figure 1, the AC/DC converter includes a PFC circuit stage, a DC/DC circuit stage and a controller. The PFC circuit stage is used to receive the AC input voltage, perform power factor correction, so that the input current has the same frequency and phase as the input voltage, thereby suppressing harmonics to avoid pollution to the grid, while outputting an output voltage with power frequency ripple.

The DC/DC circuit stage is used to convert the power output by the PFC circuit stage into the DC power required by the electronic equipment while achieving electrical isolation. For the DC/DC circuit stage, it can be implemented in the form of an LLC transformer.

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

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

As shown in Figure 2, the high-frequency switching transistors Q1 and Q2 form a high-frequency bridge arm, which works in high-frequency PWM mode, and the low-frequency switching transistors Q3 and Q4 form a low-frequency bridge arm, which works according to the power frequency switching cycle. In Figure 2, L represents the positive power supply terminal of the input AC voltage, which is connected to the first circuit node in the middle of the high-frequency switching transistors Q1 and Q2 of the high-frequency bridge arm; N represents the negative power supply terminal of the input AC voltage, which is connected to a second circuit node intermediate the high frequency switching transistors Q3 and Q4 of the high frequency bridge arm; and C1 represents 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 due to their fast reverse recovery capability. Additionally, silicon metal oxide semiconductor field effect transistors (MOSFETs) with low on-resistance can be used to implement low frequency switching transistors Q3 and Q4.

During the operation of the circuit shown in Figure 2, in the positive half cycle of the input voltage, the MOSFET switch Q4 is turned on and the MOSFET switch Q3 is turned off, and in the negative half cycle of the input voltage, the MOSFET switch Q3 is turned on and the MOSFET is switched on Tube Q4 is disconnected.

Regardless of the positive and negative half cycles of the input voltage in Figure 2, the primary current path only includes one high-frequency switch (Q1 or Q2) and one low-frequency switch (Q4 or Q3) to supply power to the load.

In order to prevent the shoot-through of the bridge arm, 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 suffers from current spikes near the zero-crossing of the AC voltage. Therefore, an external controller is usually used to control the turn-on sequence of each of the switches Q1-Q4 according to a specific sequence. As shown in FIG. 2, the gate of each switching transistor Q1-Q4 is connected to a pulse signal source provided by the controller, so the switching of each switching transistor Q1-Q4 is controlled by the pulse signal source provided by the controller.

Since the totem-pole PFC topology is known to those skilled in the art, for the sake of brevity, the basic principle of the totem-pole PFC topology will not be described in more detail here.

Existing AC/DC converters usually include a high-voltage start-up circuit, which is used to start the controller at power-on, and drives the transformer in the DC/DC circuit stage to convert the voltage to realize the normal operation of the AC/DC converter. The controller is powered by the auxiliary winding in the DC/DC circuit stage after completion.

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

On power-up of the AC input voltage, the input current charges the start 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, and the input current directly charges the boot capacitor C3 through the turned-on switching transistor Q5.

The maximum charging voltage of startup capacitor C3 is VD1-Vgsth5, where VD1 is the regulated voltage of 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-Vgsth5. For example, Vcc can be 12Vdc. At this point, the start-up is completed, and Vcc is provided through the auxiliary winding of the DC/DC circuit stage during the subsequent operation.

The high voltage start-up circuit 300 may be integrated with the PFC topology circuit 200 .

As mentioned 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, such as about 100mA, at startup. If a high voltage start-up circuit as shown in Figure 3 is used, an additional high voltage needs to be applied to switching transistor Q5 to provide sufficient current to drive the controller, eg, about 600V. This has the potential to cause overall system heating issues. Furthermore, providing such a startup current necessarily requires the use of larger capacitors. These have a detrimental effect 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 without requiring a 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 basically the same as the PFC circuit stage shown in FIG. 2, except that the switching transistor Q6 is connected in series between the low-frequency switching transistors Q3 and Q4 of the low-frequency bridge arm of FIG. 2 as a High Voltage Startup Transistor. In addition, after start-up, the switching transistor Q6 participates in the power output as a low-frequency switching transistor, and at this 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 start-up transistor Q6 is connected to the source of the low frequency switching transistor Q3 and to the second circuit node. The gate of high voltage start-up transistor Q6 is connected to the second circuit node through resistor R2 and to ground through zener diode D1. The source of the high voltage start-up transistor Q6 is connected to the drain of the low frequency switching transistor Q4. In addition, the source of high voltage startup transistor Q6 is connected to startup capacitor C3 and startup resistor R3 via ideal diode D2. The Zener diode D1 and the startup capacitor C3 here can be the same as the Zener diode D1 and the startup capacitor C3 in FIG. 3 .

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

The portion of the circuit to the right of the load capacitor C1 in Figure 5 constitutes the DC/DC circuit stage. In the embodiment shown in Figure 5, the DC/DC circuit stage is implemented by an LLC transformer. Since LLC transformers are known to those skilled in the art, for the sake of brevity, the basic principles of LLC transformers will not be described in more detail here.

As shown in FIG. 5 , when the AC/DC converter 500 is powered on, all switching transistors in the circuit are in an off state. Therefore, the input current charges the boot 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 FIGS. 4A and 4B, when the input capacitance of the switching transistor Q6 is charged to the turn-on threshold voltage Vgsth6 of the switching transistor Q6, the switching transistor Q6 is turned on. At this time, the input current directly charges the startup capacitor C3 through the turned-on switching transistor Q6.

The maximum charging voltage of start-up capacitor C3 is VD1-Vgsth6, where VD1 is the regulated voltage of 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-Vgsth6. At this point the start-up is over, and Vcc is supplied through the auxiliary winding P2 of the DC/DC circuit stage during the subsequent operation, as shown in FIG. 5 .

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

According to the embodiments 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 the controller can be provided, avoiding the above-mentioned problems in the prior art.

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

According to the embodiments of the present disclosure, a high-voltage startup circuit can be integrated into the PFC topology. Such a high-voltage startup circuit has the advantages of small startup voltage and small circuit size, and can greatly reduce the cost of an AC/DC converter using the PFC topology. manufacturing cost.

Although the high voltage start-up circuit according to the embodiment of the present disclosure is described above with a totem-pole PFC topology, those skilled in the art will recognize that the high-voltage start-up circuit according to the embodiment of the present disclosure can also be applied to other PFC topologies, For example the pseudo-totem-pole PFC topology.

Although the present disclosure has been disclosed above by describing specific embodiments of the present disclosure, it should be understood that various modifications, improvements or equivalents of the present disclosure can be devised by those skilled in the art within the spirit and scope of the appended claims thing. Such modifications, improvements or equivalents should also be considered to be included within the scope of protection of the present disclosure.

Claims (9)

1. A high voltage start-up circuit for a power factor corrector circuit, comprising: a switching transistor, connected in series between two low-frequency switching transistors in the low-frequency bridge arm of the power factor corrector circuit, wherein the drain of the switching transistor is connected to the AC input terminal, the gate of the switching transistor is connected to the AC input terminal via a resistor and to ground via a Zener diode, and the source of the switching transistor is connected via a startup capacitor arrived. 2. The high voltage start-up circuit of claim 1, wherein the power factor corrector circuit is a totem pole power factor corrector circuit. 3. The high voltage start-up circuit of claim 1, wherein the power factor corrector circuit is a pseudo-totem pole power factor corrector circuit. 4. The high voltage start-up circuit of claim 1, wherein the high frequency bridge arm of the power factor corrector circuit comprises two gallium nitride high electron mobility transistors connected in series. 5. The high voltage start-up 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 according to any one of claims 1 to 5. 7. An AC/DC converter, comprising: The power factor corrector circuit of claim 6; DC/DC circuits; 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.

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