Current protection circuit, pfc circuit, and ac / dc converter

Abstract

The present disclosure provides a current protection circuit for a power factor corrector (PFC) circuit, a PFC circuit having the current protection circuit, and an AC / DC converter having the PFC circuit. The current protection circuit according to the present disclosure senses a reverse current flowing through a low-frequency switching transistor of the PFC circuit and sends the sensed reverse current to a controller of the PFC, wherein the controller turns off the low-frequency switching transistor and a high-frequency switching transistor of the power factor corrector circuit when the sensed reverse current is greater than a pre-set reverse current threshold. The current protection circuit according to the present disclosure enables to avoid a short circuit in the PFC circuit even in the case of a sudden change in polarity of an input voltage, thereby ensuring safety of devices of the PFC topology.

Description

Technical Field

[0001] This disclosure relates to the technical field of power supplies, and more specifically, to current protection circuits for power factor correction (PFC) topologies. Furthermore, this disclosure also relates to PFC circuits having such current protection circuits and AC / DC converters using such PFC circuits. Background Technology

[0002] Many electronic devices require AC / DC converters to convert low-frequency AC mains power into DC power that can be directly used by the electronic devices. PFC topology is widely used in AC / DC converters due to its advantages such as fewer components, low common-mode noise, and high conversion efficiency.

[0003] PFC topologies require switching devices to disconnect before the zero-crossing point of the input voltage to prevent short circuits and damage to the circuit system. However, existing current protection circuits for PFC topologies are ineffective against input voltages with sudden polarity changes, such as those with square wave waveforms. Summary of the Invention

[0004] A brief overview of this disclosure is given below to provide a basic understanding of certain aspects of it. However, it should be understood that this overview is not an exhaustive summary of this disclosure. It is not intended to identify key or essential parts of this disclosure, nor is it intended to limit the scope of this disclosure. Its purpose is merely to present certain concepts of this disclosure in a simplified form as a prelude to the more detailed description that follows.

[0005] In view of the above problems, the object of at least one embodiment of this disclosure is to provide a current protection circuit for a PFC topology, so that even if the polarity of the input voltage changes suddenly, a short circuit in the PFC circuit can still be avoided, thereby ensuring the safety of the device in the PFC topology.

[0006] According to one aspect of this disclosure, a current protection circuit for a power factor correction (PFC) circuit is provided, which senses a reverse current flowing through a low-frequency switching transistor of the power factor correction circuit and sends the sensed reverse current to a controller of the power factor correction circuit, wherein when the sensed reverse current is greater than a preset reverse current threshold, the controller disconnects the low-frequency switching transistor and the high-frequency switching transistor of the power factor correction circuit.

[0007] According to another aspect of this disclosure, a PFC circuit is provided, which includes the current protection circuit according to the above aspects of this disclosure.

[0008] According to another aspect of this disclosure, an AC / DC converter is provided, which includes a PFC circuit according to the above aspects of this disclosure, a DC / DC circuit, and a controller for controlling the PFC circuit and the DC / DC circuit.

[0009] The current protection circuit for PFC topology disclosed herein has the advantages of simple structure, small size and fast response, and can ensure the device safety of PFC circuit under various input voltage waveforms.

[0010] Other aspects of embodiments of this disclosure are set forth in the following description section, wherein preferred embodiments are described in detail to fully disclose embodiments of this disclosure without imposing limitations thereon. Attached Figure Description

[0011] The above and other objects, features and advantages of this disclosure will be more readily understood by referring to the following description of embodiments of this disclosure in conjunction with the accompanying drawings, in which:

[0012] Figure 1 This is a typical block diagram of a two-stage AC / DC converter;

[0013] Figure 2 This is a typical circuit diagram of a totem pole PFC topology circuit;

[0014] Figure 3 and Figure 4 This is a schematic diagram of a short circuit occurring in a totem pole PFC topology circuit;

[0015] Figure 5 This is a schematic circuit diagram of a PFC topology circuit with a parallel current protection circuit according to one embodiment of the present disclosure.

[0016] Figure 6 This is a schematic circuit diagram of a PFC topology circuit with an inline current protection circuit according to another embodiment of the present disclosure.

[0017] Figure 7A This is a waveform diagram showing the power input voltage and drain-source current flowing through the low-frequency switching transistor of the PFC circuit according to an embodiment of the present disclosure under normal operating conditions.

[0018] Figure 7B This is a waveform diagram showing the drain-source current flowing through the upper arm low-frequency switching transistor and the gate-source voltage of each low-frequency switching transistor during the transient transition from the negative half-cycle to the positive half-cycle of the PFC circuit according to an embodiment of the present disclosure; and

[0019] Figure 7CThis is a waveform diagram showing the drain-source current flowing through the lower arm low-frequency switching transistor and the gate-source voltage of each low-frequency switching transistor during the transient transition from the positive half-cycle to the negative half-cycle of the power supply input voltage of the PFC circuit according to an embodiment of the present disclosure. Detailed Implementation

[0020] In the following description, some embodiments of the present disclosure will be described in detail with reference to the accompanying illustrative drawings. When elements are indicated by reference numerals in the drawings, the same elements will be represented by the same reference numerals even if the same elements are shown in different drawings. Furthermore, in the following description of the present disclosure, detailed descriptions of known functions and configurations incorporated herein will be omitted where it may obscure the subject matter of the disclosure.

[0021] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular form is intended to include the plural form as well, unless the context otherwise indicates. It will also be understood that the terms “comprising,” “including,” and “having” as used in the specification are intended to specifically describe the presence of the 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.

[0022] Unless otherwise defined, all terms used herein, including technical and scientific terms, shall have the same meaning as commonly understood by one of ordinary skill in the art to which the inventive concept pertains. It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having the same meaning as their meaning in the context of the relevant field, and should not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0023] In the following description, numerous specific details are set forth to provide a complete understanding of this disclosure. This 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 closely related to the embodiments of this disclosure are shown in the accompanying drawings, while other details less relevant to this disclosure are omitted.

[0024] In the following, preferred embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings.

[0025] Figure 1 A typical block diagram of a two-stage AC / DC converter is shown. Figure 1As shown, the AC / DC converter includes a PFC circuit stage, a DC / DC circuit stage, and a controller. The PFC circuit stage receives the AC input voltage, performs power factor correction, and ensures that the input current has the same frequency and phase as the input voltage, thereby suppressing harmonics to avoid pollution of the power grid, while simultaneously outputting an output voltage with power frequency ripple.

[0026] The DC / DC circuit stage is used to convert the power output from the PFC circuit stage into the DC power required by electronic devices, while providing electrical isolation. The DC / DC circuit stage can be implemented using, for example, an LLC transformer.

[0027] The controller provides control signals to the PFC circuit stage and the DC / DC circuit stage. Specifically, the controller provides gate drive signals to the switching transistors in the PFC and DC / DC circuit stages. Typically, the controller is implemented using a digital signal processor (DSP).

[0028] Since two-stage AC / DC converters are known to those skilled in the art, for the sake of brevity, the circuit structure and basic principles of two-stage AC / DC converters will not be described in more detail here.

[0029] As an example, Figure 2 A typical totem pole PFC topology circuit 200 is shown.

[0030] like Figure 2 As shown, high-frequency switching transistors Q1 and Q2 form a high-frequency bridge arm, operating in high-frequency PWM mode, while low-frequency switching transistors Q3 and Q4 form a low-frequency bridge arm, operating according to the power frequency switching cycle. Figure 2 In this diagram, L (Live) represents the positive power supply terminal of the input AC voltage, which is connected to the first circuit node N1 between the high-frequency switching transistors Q1 and Q2 in the high-frequency bridge arm. N (Neutral) represents the negative power supply terminal of the input AC voltage, which is connected to the second circuit node N2 between the low-frequency switching transistors Q3 and Q4 in the low-frequency bridge arm. Furthermore, C1 represents the load capacitor.

[0031] In some embodiments of this disclosure, gallium nitride (GaN) transistors and silicon carbide (SiC) transistors can be used to implement high-frequency switching transistors Q1 and Q2. Furthermore, metal-oxide-semiconductor field-effect transistors (MOSFETs) with low on-resistance can be used to implement low-frequency switching transistors Q3 and Q4.

[0032] exist Figure 2During the operation of the circuit shown, MOSFET switching transistor Q4 is turned on and MOSFET switching transistor Q3 is turned off during the positive half-cycle of the input voltage, and MOSFET switching transistor Q3 is turned on and MOSFET switching transistor Q4 is turned off during the negative half-cycle of the input voltage.

[0033] Regardless of Figure 2 During the positive and negative half-cycles of the input voltage, the primary current path contains only one high-frequency switching transistor (Q1 or Q2) and one low-frequency switching transistor (Q4 or Q3) to supply power to the load.

[0034] To prevent bridge arm shoot-through, it is necessary to set a dead time between the two high-frequency switching transistors Q1 and Q2 in the high-frequency bridge arm. Furthermore, the totem-pole PFC topology suffers from current spikes near the AC voltage zero-crossing point. Therefore, an external controller is typically used to control the turn-on timing of each switching transistor Q1-Q4 according to a specific timing sequence. For example... Figure 2 As shown, the gates of each switching transistor Q1-Q4 are 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.

[0035] Since the totem pole PFC topology is known to those skilled in the art, for the sake of brevity, the basic principles of the totem pole PFC topology will not be described in more detail here.

[0036] For totem-pole PFC topology, it is required that each switching transistor Q1-Q4 be disconnected before the AC input voltage crosses zero to avoid short circuits.

[0037] Figure 3 and Figure 4 A schematic diagram of a short circuit occurring in the totem pole PFC topology circuit 200 is shown.

[0038] like Figure 3 As shown in the figure, assuming that the current input voltage of the PFC circuit 200 is in the negative half-cycle, at this time the MOSFET switching transistor Q3 is turned on and the MOSFET switching transistor Q4 is turned off, and the current flow is as shown by the dashed arrow A1.

[0039] like Figure 4As shown, if the polarity of the input voltage changes suddenly, for example, if the input voltage has a square wave waveform or a transient phenomenon occurs in the power supply line, causing the input voltage to suddenly jump from the negative half-cycle to the positive half-cycle, while the MOSFET switching transistor Q3 may still be in the conducting state, a surge current, represented by the solid arrow A2, will flow through the freewheeling diode (not shown) connected in reverse parallel with the high-frequency switching transistor Q1 or the body diode of Q1 itself, which acts as a freewheeling diode. Therefore, a short circuit occurs in the PFC circuit 200, potentially damaging the devices. At this time, the current flow direction A2 is opposite to the current flow direction A1 when the switching transistor Q3 is operating normally. In this paper, the current opposite to the normal operating current flowing through the low-frequency switching transistors Q3 and Q4 is called the reverse current.

[0040] although Figure 3 and Figure 4 Only the case where the polarity of the input voltage abruptly changes from the negative half-cycle to the positive half-cycle is shown. However, those skilled in the art will recognize that when the polarity of the input voltage abruptly changes from the positive half-cycle to the negative half-cycle, a short circuit may occur in the PFC circuit 200 via the switching transistor Q4. The current protection circuit proposed in this paper is also applicable to this short circuit phenomenon.

[0041] When the AC input voltage has an ideal sinusoidal waveform, the arrival of the zero-crossing point can be predicted by sensing the input voltage. Short circuits can be avoided by disconnecting low-frequency switching transistors Q3 and Q4 before the zero-crossing point. However, for conditions such as... Figure 3 and Figure 4 In the case of a sudden change in the polarity of the input voltage shown, there is a delay in the existing protection circuit for sensing the input voltage. Often, a serious short circuit problem has occurred before the controller outputs the control signal to turn off the low-frequency switching transistors Q3 and Q4.

[0042] To address the aforementioned issues, this paper proposes a current protection circuit for PFC circuits, which can promptly detect sudden changes in the polarity of the input voltage and respond quickly to avoid adverse effects of short circuits in PFC circuits on the devices.

[0043] As mentioned above Figure 3 and Figure 4 As stated, when a short circuit occurs in the PFC circuit 200, the current direction changes as indicated by arrows A1 and A2.

[0044] Therefore, the current protection circuit according to this disclosure determines whether there is a short circuit in the circuit by detecting the occurrence of a large reverse current, and controls the on / off state of each switching transistor accordingly.

[0045] According to embodiments of this disclosure, the current protection circuit can sense the reverse current flowing through the low-frequency switching transistor of the PFC circuit and send the sensed reverse current to the controller of the PFC circuit. When the sensed reverse current exceeds a preset reverse current threshold, the controller can disconnect the low-frequency switching transistor and the high-frequency switching transistor of the PFC circuit.

[0046] Figure 5 A schematic circuit diagram of a PFC circuit 500 of a parallel current protection circuit 501 according to one embodiment of the present disclosure is shown. Figure 5 Zhongyu Figure 2 The same devices are represented by the same symbols.

[0047] According to an embodiment of this disclosure, the current protection circuit 501 can sense the current flowing through the low-frequency switching transistor in the low-frequency bridge arm and provide the current sensing result to the controller (not shown).

[0048] Specifically, according to embodiments of the present disclosure, the current protection circuit 501 may include a current sensing resistor R1 serving as a first current sensing unit and a current sensing resistor R2 serving as a second current sensing unit.

[0049] According to an embodiment of this disclosure, one end of resistor R1 is connected to the source of the upper arm low-frequency switching transistor Q3, and the other end is connected to the second circuit node N2. By measuring the voltage across resistor R1, a large reverse current flowing through the upper arm low-frequency switching transistor Q3 can be sensed, thereby determining whether a short circuit exists in the circuit. The current measurement result of resistor R1 is transmitted to the controller.

[0050] Similarly, according to an embodiment of this disclosure, one end of resistor R2 is connected to the drain of the lower arm low-frequency switching transistor Q4, and the other end is connected to the second circuit node N2. By measuring the voltage across resistor R2, a large reverse current flowing through the lower arm low-frequency switching transistor Q4 can be sensed, thereby determining whether a short circuit exists in the circuit. The current measurement result of resistor R2 is transmitted to the controller.

[0051] Preferably, resistors R1 and R2 can be high-precision resistors with small resistance values ​​and small temperature coefficients. Small resistance values ​​can avoid adverse effects on circuit power consumption when circuit 500 is operating normally, while small temperature coefficients can minimize the impact of temperature changes on current sensing accuracy.

[0052] According to embodiments of this disclosure, the controller can determine whether a short circuit exists in the PFC circuit 500 based on the current sensing results of current sensing resistors R1 and R2. For example, a reverse current threshold can be set, which can be determined based on factors such as circuit topology. For example, the reverse current threshold can be 20A.

[0053] When the reverse current sensed by resistors R1 and R2 is greater than the reverse current threshold, it is determined that there is a short circuit in the PFC circuit 500. Therefore, the controller sends control signals to each switching transistor Q1-Q4 to disconnect them, thereby protecting the circuit.

[0054] Although embodiments of this disclosure use current-sensing resistors R1 and R2 to sense the current flowing through low-frequency switching transistors Q3 and Q4, this disclosure is not limited thereto. Based on the teachings of this disclosure, those skilled in the art can conceive of other variations for sensing large reverse currents flowing through low-frequency switching transistors. For example, the detection of current flowing through low-frequency switching transistors can be achieved by using inductors (DCRs), current transformers, Hall effect devices, sensing the voltage across the drain-source on-resistance of low-frequency switching transistors Q3 and Q4, and other variations. Furthermore, for example, the detection of current flowing through low-frequency switching transistors can also be achieved using different circuit topologies that connect the current-sensing resistors in parallel with the low-frequency switching transistors. All these variations should be covered within the scope of this disclosure.

[0055] According to embodiments of this disclosure, when a large reverse current is reset, the controller can re-turn on each switching transistor Q1-Q4 after a predetermined delay time. According to embodiments of this disclosure, this delay time can be determined based on the specific circuit topology, and is, for example, 1 ms.

[0056] Figure 6 A schematic circuit diagram of a PFC circuit 600 of a parallel current protection circuit 601 according to another embodiment of the present disclosure is shown. Figure 6 Zhongyu Figure 2 and Figure 5 The same devices are represented by the same symbols.

[0057] Figure 6 circuit structure and Figure 5 The circuit structures are basically the same, the difference is that Figure 6 The current protection circuit 601 shown also includes an inductor L1. The inductor L1 is used to reduce the impact of large reverse currents on the overall circuit, i.e., to reduce the rate of change of the reverse current di / dt, where i represents the reverse current. By reducing the rate of change of large reverse currents, time can be gained for the controller to respond promptly to potential short circuits.

[0058] According to an embodiment of this disclosure, one end of inductor L1 is connected to the negative power supply terminal N, and the other end is connected to the second circuit node N2.

[0059] The current protection circuit according to this disclosure has the advantages of simple structure and easy integration. Furthermore, the PFC circuit employing the current protection circuit according to this disclosure reduces the impact of short circuits on circuit devices when the polarity of the AC input voltage suddenly changes, thereby achieving device protection.

[0060] Figure 7A The diagram shows waveforms of the power input voltage Vin and the drain-source currents Ids-Q3 and Ids-Q4 flowing through low-frequency switching transistors Q3 and Q4 under normal operating conditions for a PFC circuit according to an embodiment of the present disclosure. Furthermore, Figure 7B The diagram shows the waveforms of the power input voltage Vin of the PFC circuit according to an embodiment of the present disclosure, as well as the drain-source current Ids-Q3 flowing through the low-frequency switching transistor Q3 and the gate-source voltages Vgs-Q3 and Vgs-Q4 of the low-frequency switching transistors Q3 and Q4 during the transient transition from the negative half-cycle to the positive half-cycle. Figure 7C The diagram shows the waveforms of the power input voltage Vin of the PFC circuit according to an embodiment of the present disclosure, the drain-source current Ids-Q4 flowing through the low-frequency switching transistor Q4, and the gate-source voltages Vgs-Q3 and Vgs-Q4 of the low-frequency switching transistors Q3 and Q4 during the transient transition from the positive half-cycle to the positive half-cycle.

[0061] like Figure 7B As shown in the figure, it is assumed that a transient phenomenon occurs in the input voltage Vin from the negative half-cycle to the positive half-cycle (in Figure 7B As shown at point A). With the current protection circuit according to the embodiment of this disclosure, since a large reverse current appears in the low-frequency switching transistor Q3 (reaching the reverse current threshold shown at point B), the controller turns off all switching transistors (especially the low-frequency switching transistor Q3), thereby reducing the drain-source current Ids-Q3 of the low-frequency switching transistor Q3 and preventing short circuits in the circuit from damaging the device.

[0062] like Figure 7C As shown in the figure, it is assumed that a transient phenomenon occurs in the input voltage Vin from the positive half-cycle to the negative half-cycle (in Figure 7C As shown at point A). With the current protection circuit according to the embodiment of this disclosure, since a large reverse current appears in the low-frequency switching transistor Q4 (reaching the reverse current threshold shown at point B), the controller turns off all switching transistors (especially the low-frequency switching transistor Q4), thereby reducing the drain-source current Ids-Q4 of the low-frequency switching transistor Q4 and preventing damage to the device from a short circuit in the circuit.

[0063] Although the current protection circuit according to an embodiment of the present disclosure has been described above with reference to a totem pole PFC topology, those skilled in the art will recognize that the current protection circuit according to an embodiment of the present disclosure can also be applied to other PFC topologies, such as pseudo-totem pole PFC topologies.

[0064] Although this disclosure has been described above through a specific embodiment, it should be understood that those skilled in the art can devise various modifications, improvements, or equivalents to this disclosure within the spirit and scope of the appended claims. Such modifications, improvements, or equivalents should also be considered to be included within the scope of this disclosure.

Claims

1. A current protection circuit for a power factor correction circuit, configured to sense a reverse current flowing through a low-frequency switching transistor of the power factor correction circuit, and to send the sensed reverse current to a controller of the power factor correction circuit. in, The low-frequency switching transistor includes an upper arm low-frequency switching transistor and / or a lower arm low-frequency switching transistor, and When the sensed reverse current exceeds a preset reverse current threshold, the controller disconnects the low-frequency and high-frequency switching transistors of the power factor corrector circuit.

2. The current protection circuit according to claim 1, comprising: The first current sensing unit has one end connected to the source of the upper arm low-frequency switching transistor and the other end connected to the circuit node between the upper arm low-frequency switching transistor and the lower arm low-frequency switching transistor. as well as The second current sensing unit has one end connected to the drain of the lower arm low-frequency switching transistor and the other end connected to the circuit node.

3. The current protection circuit according to claim 2, wherein each of the first current sensing unit and the second current sensing unit includes a current sensing resistor.

4. The current protection circuit according to claim 2 further includes: An inductor, one end of which is connected to a negative power source, and the other end of which is connected to a circuit node between the upper arm low-frequency switching transistor and the lower arm low-frequency switching transistor.

5. The current protection circuit according to claim 1, wherein the high-frequency switching transistor is a gallium nitride transistor or a silicon carbide transistor.

6. The current protection circuit according to claim 1, wherein the low-frequency switching transistor is a metal-oxide-semiconductor field-effect transistor.

7. The current protection circuit of claim 1, wherein when the sensed reverse current is reset, the controller turns on the low-frequency switching transistor and the high-frequency switching transistor after a preset delay time.

8. A power factor correction circuit, comprising a current protection circuit according to any one of claims 1 to 7.

9. An AC / DC converter, comprising: The power factor correction circuit according to claim 8; DC / DC circuits; as well as A controller that controls the power factor corrector circuit and the DC / DC circuit.

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