Overvoltage protection for a synchronous power rectifier

A circuit is described that includes a rectifier configured to rectify a DC output from an AC input, a sensing unit configured to detect a voltage level of the DC output, and a control unit configured to control the rectifier based on the voltage level of the DC output. The control unit is configured to control the rectifier output by at least controlling the rectifier to rectify the DC output from the AC input if the voltage level of the DC output does not indicate an overvoltage condition at the circuit. In addition, the control unit is configured to control the rectifier based on the voltage level of the DC output by at least controlling the rectifier to shunt current from the AC input if the voltage level of the DC output does indicate the overvoltage condition.

TECHNICAL FIELD

This disclosure relates to techniques and circuits related to synchronous power rectifiers.

BACKGROUND

Some power applications include one or more rectifiers to convert AC voltages to DC voltages. For instance, a wireless power receiver may rely on a rectifier to convert an AC voltage input received at a receiving coil into a DC voltage that is relied on by some other part of the wireless power receiver (e.g., a power converter, a load, etc.). A rectifier may be a passive rectifier or a synchronous rectifier (otherwise referred to as “active rectifier”). A passive rectifier may include passive elements (e.g., diodes) and a synchronous rectifier may include active elements (e.g., controllable switches). In either case, the elements of a passive and synchronous rectifier are arranged in a particular configuration (e.g., a half-bridge, an H-bridge configuration) to convert an AC voltage to DC. By using active type elements rather than passive type elements, a synchronous rectifier may have a reduced amount of power loss as compared to a passive rectifier.

In some examples, the active type elements of a synchronous rectifier may be Metal Oxide Semiconductor (MOS) type switches and that each include a parasitic body diode. A body diode of each MOS type switch may act like a passive type element of a passive rectifier. Accordingly, even when each MOS type switch of a synchronous rectifier is operating in a switched-off state, the synchronous rectifier may still perform passive rectification. Accordingly, if a large AC voltage is applied to the input of a synchronous rectifier when the MOS type switches are turned-off, the synchronous rectifier may still output a large DC voltage (e.g., a DC voltage that exceeds the breakthrough voltage of the MOS type switches) that can destroy or at least damage the synchronous rectifier and/or surrounding system.

SUMMARY

In general, circuits and techniques of this disclosure may provide protection to a synchronous rectifier from overvoltage conditions without the use of voltage clamps (e.g., high-voltage capacitors at the input to the rectifier) or other types of external components. Through control of the switches of a rectifier, the controller may cause the rectifier to output a rectified DC voltage based on an AC voltage input. However, rather than simply control the switches of the synchronous rectifier to perform rectification, the controller described herein may further control the switches to prevent overvoltage conditions from damaging the rectifier. For example, based on the voltage level of the DC output of the rectifier, the controller may determine whether to adjust the operational state of any of the switches of the rectifier to cause the rectifier to begin operating in a protection mode, thereby resulting in a reduction of the voltage level of the DC output.

In one example, the disclosure is directed to a circuit that includes a rectifier configured to rectify a DC output from an AC input and a sensing unit configured to detect a voltage level of the DC output. The circuit further comprises a control unit configured to control the rectifier based on the voltage level of the DC output by at least controlling the rectifier to: rectify the DC output from the AC input if the voltage level of the DC output does not indicate an overvoltage condition at the circuit; and shunt current from the AC input if the voltage level of the DC output does indicate the overvoltage condition.

In another example, the disclosure is directed to a method that includes detecting a voltage level of a DC output from a rectifier that receives an AC input; determining, by a control unit, whether the voltage level indicates an overvoltage condition at the rectifier; and rectifying, with the rectifier, the DC output if the voltage level of the DC output does not indicate the overvoltage condition. The method further includes shunting current from the AC input, with the rectifier, if the voltage level of the DC output does indicate the overvoltage condition.

In another example, the disclosure is directed to a circuit having means for detecting a voltage level of a DC output from a rectifier that receives an AC input, means for determining whether the voltage level indicates an overvoltage condition at the rectifier, and means for rectifying the DC output if the voltage level of the DC output does not indicate the overvoltage condition. The circuit has further means for shunting current from the AC input if the voltage level of the DC output does indicate the overvoltage condition.

DETAILED DESCRIPTION

Some power applications include one or more rectifiers to convert AC voltages to DC voltages. For instance, a wireless power receiver may rely on a rectifier to convert an AC voltage input received at a receiving coil into a DC voltage that is relied on by some other part of the wireless power receiver (e.g., a step-up or step-down converter, a load, etc.). A rectifier may be a passive rectifier or a synchronous rectifier (otherwise referred to as “active rectifier”) active rectifier. A passive rectifier may include passive elements (e.g., diodes) and a synchronous rectifier may include active elements (e.g., controllable switches). In either case, the elements of a passive and synchronous rectifier are arranged in a particular configuration (e.g., a half-bridge, an H-bridge configuration) to convert an AC voltage to DC. By using active type elements rather than passive type elements, a synchronous rectifier may have a reduced amount of power loss as compared to a passive rectifier.

In some examples, the active type elements of a synchronous rectifier may comprise Metal Oxide Semiconductor (MOS) type switches and that each include a parasitic body diode. A body diode of each MOS type switch may act like a passive type element of a passive rectifier. Accordingly, even when each MOS type switch of a synchronous rectifier is operating in a switched-off state, the synchronous rectifier may still perform passive rectification.

Referring back to the example wireless power receiver described above, a receiving coil may be exposed to potential signals traveling through the air. If the rectifier of the wireless power receiver is a synchronous rectifier that relies on MOS type switches, any signal that the receiving coil captures, even when the synchronous rectifier is switched-off, has the potential to be rectified. For example, if the receiving coil receives a large AC voltage when the synchronous rectifier is switched-off, a large, unintended DC voltage may be rectified at the output of the synchronous rectifier. An unintended DC voltage at the output of the rectifier, especially if the DC voltage exceeds the breakthrough voltage of the MOS type switches, can destroy or at least damage the synchronous rectifier and/or portion of wireless power receiver that is coupled to the output of the synchronous rectifier.

To prevent a synchronous rectifier from producing unintended DC voltage outputs when such a synchronous rectifier is switched-off, some wireless power receivers and other types of power applications may rely on voltage clamps to block the unintended AC voltage from reaching the synchronous rectifier. For example, a voltage clamp in this context may take the form of a high-voltage capacitor that is coupled to ground and in series with a switch and a respective input terminal of the synchronous rectifier. Each input terminal to the synchronous rectifier may have one or more voltage clamps. When a controller causes the MOS type switches of the synchronous rectifier to switch-off and/or when the controller senses an overvoltage at the output of the synchronous rectifier, the controller also causes the respective switch of each voltage clamp to close, in essence, grounding the input terminals to the synchronous rectifier. By activating each voltage clamp, any potential current that could otherwise enter or has otherwise entered the synchronous rectifier is shunted away from the input terminals and to each grounded capacitor. Drawbacks to voltage clamps such as these are that additional pins, switches, components, etc. are required for their implementation. The additional components and connections may cause an increase in size, area, cost, and/or complexity of the overall system. High voltage capacitors of the type used in such a voltage clamp may be designed to withstand abnormally high voltages and currents. These high voltage capacitors can be particularly cost prohibitive for some applications.

In general, circuits and techniques of this disclosure may provide protection to a synchronous rectifier from overvoltage conditions without the use of voltage clamps (e.g., high-voltage capacitors at the input to the rectifier) or other types of external components. A controller may generally control the operation of the switches of the synchronous rectifier, for example, by providing signals to the rectifier that cause one or more of the switches to transition between operating in an on-state and an off state). Through control of the switches, the controller may cause the rectifier to output a rectified DC voltage based on an AC voltage input.

Rather than merely controlling the switches of a synchronous rectifier to perform rectification, a controller according to the circuits and techniques of this disclosure may further control the switches of the rectifier in such a way as to prevent an overvoltage condition at the rectifier from causing damage to the rectifier. The controller may determine the voltage level at the output of the rectifier and based on the output voltage level, determine whether to adjust the operational state of any of the switches. In the event that the controller determines that an overvoltage is occurring or is about to occur at the rectifier, the controller may cause the rectifier to begin operating in a protection mode. During the protection mode, the rectifier is configured to shunt current away from the AC input of the rectifier to reduce the voltage level of the DC output of the rectifier.

For example, the controller may compare the voltage level at the output to a threshold for determining whether an overvoltage (e.g., a voltage that if present at the rectifier could damage the rectifier) condition may be present. If based on the comparison, the controller determines that the rectified voltage level at the output is nearing the voltage level associated with an overvoltage condition, the controller may partially or completely disable one or more of the switches of the rectifier (e.g., one or more of the high-side switches) and may partially or completely enable one or more of the other switches of the rectifier (e.g., one or more of the low-side switches) to reduce the rectified voltage level back down to tolerable levels.

By relying on a rectified output voltage in controlling the operational state of the switches of a synchronous rectifier, the controller can prevent the rectifier from overvoltage conditions that would otherwise damage the rectifier. In this way, a rectifier can have protection from overvoltage conditions without the use of expensive external components. A power converter that controls a synchronous rectifier according to the circuits and techniques of this disclosure may be less expensive and or smaller in size than some other power converters that rely on external protection components, such as high-voltage capacitors.

FIG. 1is a block diagram illustrating an example system for rectifying an AC voltage from an AC supply, in accordance with one or more aspects of the present disclosure.FIG. 1shows system1as having four separate and distinct components shown as AC supply2, power converter4, filter6, and DC DC load8, however system1may include additional or fewer components. For instance, AC supply2, power converter4, filter6, and DC DC load8may be four individual components or may represent a combination of one or more components that provide the functionality of system1as described herein.

System1includes AC supply2which provides AC electrical power (to system1. Numerous examples of AC supply2exist and may include, but are not limited to, power grids, generators, transformers or any other form of devices that are capable of providing AC power to system1. AC supply2may provide an AC voltage and/or AC current across link10to power converter4.

Power converter4represents an AC-to-DC power converter which converts the AC power provided by AC supply2into DC power for powering DC load8. Power converter4includes one or more receiving coils, rectifiers, step-up or step-down converters, filters, and/or other components to convert the voltage and/or current associated with the power received from AC supply2into a usable form of DC power for use by DC load8. For example, power converter4may be a wireless power receiver that converts wireless AC energy into a DC voltage output. In some examples, power converter4includes a control unit to control the operation of power converter4. For instance, the control unit of power converter4may control when and at what magnitude power converter4outputs a DC voltage at link12.

Filter6and DC load8represent optional components of system1. DC load8may receive the DC power (e.g., voltage, current, etc.) converted by power converter4after the DC power passes through filter6. In some examples, DC load8uses the filtered DC power from power converter4and filter6to perform a function. Numerous examples of filter6exist and may include, any suitable electronic filter for filtering power for a load. Examples of filter6include, but are not limited to, passive or active electronic filters, analog or digital filters, high-pass, low-pass, band pass, notch, or all-pass filters, resistor-capacitor filters, inductor-capacitor filters, resistor-inductor-capacitor filters, and the like. Likewise, numerous examples of DC load8exist and may include, but are not limited to, charging circuits, computing devices and related components, such as microprocessors, electrical components, circuits, laptop computers, desktop computers, tablet computers, mobile phones, batteries, speakers, lighting units, automotive/marine/aerospace/train related components, motors, transformers, or any other type of electrical device and/or circuitry that receives a voltage or a current from a power converter.

AC supply2may provide AC power (e.g., power which has an AC voltage level or AC current level) over link10. DC load8may receive DC power (e.g., power which has a DC voltage level or DC current level) converted by power converter4, and filtered through filter6, over link14. Links10,12, and14represent any medium capable of conducting electrical power from one location to another.

Examples of links10,12, and14include, but are not limited to, physical and/or wireless electrical transmission mediums such as electrical wires, electrical traces, conductive gas tubes, twisted wire pairs, and the like. Each of links10and12may provide electrical coupling between, respectively, AC supply2and power converter4, and power converter4and filter6. Link14provides electrical coupling between filter6and DC load8. In addition, link14provides a feedback loop or circuit for carrying information to power converter4associated with the characteristics of a filtered power output from filter6. In the example ofFIG. 1, link10is a wireless link for wirelessly transmitting AC power, however in other examples, link10may be a wired or physical link.

In the example of system1, power converter4may rectify the AC voltage of the AC power delivered by AC supply2to a DC voltage of DC power that meets the power requirements of DC load8. For instance, AC supply2may output, and power converter4may receive, power which has an AC voltage level at link10. Power converter4may convert (e.g., rectify) the power which has the AC voltage level to power which has a DC voltage level that is required by DC load8. Power converter4may output the power that has the DC voltage level at link12. Filter6may receive the power from converter4and output the filtered power that has the DC voltage level at link14. DC load8may receive the filtered power that has the DC voltage level at link14. DC load8may use the filtered power having the DC voltage level to perform a function (e.g., power a microprocessor).

FIG. 2is a block diagram illustrating one example of power converter4of system1shown inFIG. 1which uses voltage clamps for overvoltage protection. For instance,FIG. 2shows power converter4A as a more detailed exemplary view of power converter4of system1fromFIG. 1and the electrical connections to AC supply2, filter6, and DC load8, provided by links10,12, and14respectively. As described below, power converter4A uses voltage clamps36A and36B for overvoltage protection.

Power converter4A is shown as being a wireless power receiver configured to receive an AC power input via wireless link10and output DC power via link12. Power converter4A includes receiving (“RX”) coil32coupled to synchronous rectifier34(referred to simply as “rectifier34”).

RX coil32includes inductor26and capacitors24A and24B. RX coil may receive an AC power input via wireless link10and output an AC current and/or AC voltage associated with the AC power input at nodes18A and18B (e.g., the cathode terminal and anode terminal of capacitor24B). Rectifier34may receive the AC current and/or AC voltage from RX coil32at nodes18A and18B and rectify the AC current and/or AC voltage to a rectified DC current and/or rectified DC voltage output at link12.

Rectifier34includes high-side switches20A and20B (collectively referred to herein as “switches20”) and low-side switches22A and22B (collectively referred to herein as “switches22”). Switches20and22represent MOS type switch devices that are arranged in a H-bridge configuration for rectifying an AC voltage input received at nodes18A and18B into a DC voltage output at link12. In some examples, switches20and22of rectifier34may include additional and/or fewer switches. In addition, other configurations of switches20and22may exist including half-bridge configurations and the like.

Switches20and22may each receive a respective control signal via one of links16that causes the respective switch to transition between operating in an on-state and an-off state. As used herein, the term “on-state” reflects an operating state of each of switches20and22that corresponds to the switch being “switched-on,” “turned-on,” “closed,” and/or “enabled.” The term “off-state” reflects an operating state of each of switches20and22that corresponds to the switch being “switched-off,” “turned-off,” “opened,” and/or “disabled.” The operating state of each of switches20and22may depend at any particular time on the respective signal being received over link16.

Power converter4A includes control unit30A for controlling rectifier34to rectify a DC voltage output at link12. In other words, control unit30A represents a combination of driver/control logic of power converter4A for performing rectification techniques to control switches20and22to produce a rectified DC voltage at link12. Control unit30A may issue control signals via links16that cause one or more of switches20and22transition between operating in an on-state and an-off state. For example, control unit30A may issue control signal via link16that cause switches20A and22B to switch-on and switches20B and22A to switch-off. Control unit30A may issue a subsequent control signal via link16that causes switches20A and22B to switch-off and switches20B and22A to switch-on. Control unit30A can issue commands or signals via links16that cause switches20and22to transition between operating in respective on-states and/or off-states in various patterns and at various times in order to cause rectifier34to produce a rectified voltage output at link12.

To protect power converter4A from overvoltage conditions, power converter4A relies on active voltage clamps36A and36B coupled to nodes18A and18B (e.g., the input to rectifier34). Voltage clamp36A includes switch28A that when closed, couples grounded high-voltage capacitor26A to node18A. Closing switch28A “enables” voltage clamp36A for providing overvoltage protection for rectifier34. Voltage clamp36B includes switch28B that when enabled, couples grounded high-voltage capacitor26B to node18B. Closing switch28B “enables” voltage clamp36B for providing overvoltage protection for rectifier34. Control unit30A may issue one or more commands or signals via links16to enable voltage clamps36A and36B.

The control unit30A may enable voltage clamps36A and36B when control unit30A detects an overvoltage condition at the output of power converter4A (e.g., at link12). For example, control unit30A may detect a current and/or voltage condition at link12and determine that the voltage may be exceeding the operating limits of rectifier34. To prevent rectifier34from being damaged from the overvoltage at the input of rectifier34, control unit30A may generate one or more commands or signals at links16that enable voltage clamps36A and36B. In this way, charge (e.g., current) at the input to rectifier34from RX coil36is shunted away from rectifier34during the overvoltage. When control unit30A determines that the overvoltage condition is over, control unit30A may disable voltage clamps36A and36B to allow rectifier34to again receive current from RX coil.

There are numerous drawbacks to power converter4A and the use of voltage clamps, such as voltage clamps36A and36B for overvoltage protection. For example, each of voltage clamps36A and26B represent additional external components beyond RX coil32, rectifier34, and control unit30A and therefore may increase the overall size, area, and/or complexity of power converter4A. Furthermore, each of voltage clamps36A and26B represent potentially costly (e.g., expensive) components. For instance, capacitors26A and26B may be expensive high-voltage capacitors which are rated to withstand a high voltage and/or high current. The use of potentially expensive voltage clamps36A and36B may therefore increase overall cost of power converter4A.

FIG. 3is a block diagram illustrating one example of power converter4of system1shown inFIG. 1which has overvoltage protection in accordance with one or more aspects of the present disclosure. For instance,FIG. 2shows power converter4B as a more detailed exemplary view of power converter4of system1fromFIG. 1and the electrical connections to AC supply2, filter6, and DC load8, provided by links10,12, and14respectively. As described below, power converter4B offers various advantages over power converter4A. For example, rather than rely on additional, and potentially expensive voltage clamps, such as voltage clamps36A and36B, power converter4B may perform overvoltage protection through careful control of switches20and22of rectifier34.

Power converter4B includes RX coil32coupled directly to rectifier34without the use of any voltage clamps at the input to rectifier34. Power converter4B further includes control unit30B in addition to voltage sense unit38.

Rectifier34includes four switches20and22(shown as MOS type switches) arranged in an H-bridge configuration. In some examples, rectifier34may include fewer than four switches or more than four switches. For example, switches20and22may be only two switches arranged in a half-bridge configuration or any other arrangement of more than four switches that can be used by rectifier34to produce a rectified voltage output at link12.

In the example ofFIG. 3, each of switches20and22of rectifier34are active switching elements capable of conducting current in a passive mode. For instance, each of switches20and22represent MOS type switches that each include respective body diodes configured to conduct current, even when switched-off, when the voltage across each of switches20and22exceeds the breakthrough voltage of each respective body diode. In some examples, high-side switches20may not be active switching elements and may instead be passive switching elements, such as diodes. Any active switching elements of rectifier34, whether just low-side switches22or both low-side switches22and high-side switches20, have body diodes (e.g., to also act as passive rectifier in case of turned-off switches, as is the case with MOS transistors). In some examples, high-side switches20may be either NMOS (with bootstrap driver) or PMOS switches.

Control unit30B is used by power converter4B to control rectifier34to rectify a DC voltage output at link12based on an AC power input at link10. In other words, control unit30B represents a combination of driver/control logic of power converter4B for performing rectification techniques to control switches20and22of rectifier34to produce a rectified DC voltage at link12. Control unit30B may issue control signals via links16that cause one or more of switches20and22transition between operating in an on-state and an-off state. For example, control unit30B may issue control signal via link16that cause switches20A and22B to switch-on and switches20B and22A to switch-off. Control unit30B may issue a subsequent control signal via link16that causes switches20A and22B to switch-off and switches20B and22A to switch-on. Control unit30B can issue commands or signals via links16that cause switches20and22to transition between operating in respective on-states and/or off-states in various patterns and at various times in order to cause rectifier34to produce a rectified voltage output at link12.

Control unit30B can comprise any suitable arrangement of hardware, software, firmware, or any combination thereof, to perform the techniques attributed to control unit30B herein. In some examples, control unit30B includes only digital control logic, only analog control logic, or in some examples, a combination of digital and analog control logic.

For example, control unit30B may include digital circuitry, analog circuitry, or any combination thereof to control and regulate a switch mode power converter. Control unit30B may include any one or more microprocessors, signal processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), comparators, operational amplifiers, full-custom and/or semi-custom digital logic, registers for storing control data (e.g., parameters), analog and/or digital filter stages, non-linear control blocks, or any other equivalent, integrated, digital or analog circuitry, as well as any combinations of such components.

When control unit30B includes software or firmware, control unit30B further includes hardware for storing and executing the software or firmware, such as one or more digital or analog processors or processing units. In general, a processing unit may include one or more microprocessors, signal processors, ASICs, FPGAs, comparators, operational amplifiers, or any other equivalent, integrated, digital or analog circuitry, as well as any combinations of such components. Although not shown, control unit30B may include a memory configured to store data. The memory may include any volatile or non-volatile media, such as a random access memory (RAM), read only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, and the like. In some examples, the memory may be external to control unit30B and/or power converter4B, e.g., may be external to a package in which control unit30A and/or power converter4B is housed.

Voltage sense unit38is coupled to link12(e.g., the output of rectifier34) for determining or measuring a voltage level at link12from which controller unit30B may detect an overvoltage condition. For example, voltage sense unit38represents any combination of digital and/or analog circuitry capable of providing information via link40that is indicative of the voltage level at link12. Examples of voltage sense unit38are a voltage comparator, an analog to digital converter (ADC), a protection clamp current drain, and the like. Voltage sense unit38represents any combination of hardware, software, and/or firmware for detecting a voltage level at the output of rectifier34.

In accordance with circuits and techniques disclosed herein, control unit30B may obtain a voltage level of a rectified DC voltage that rectifier34outputs at link12via a connection that control unit30B shares with voltage sense unit38at link40. Converter4B may rely on the voltage level of the rectified DC voltage to determine whether an overvoltage condition at power converter4B is occurring or is about to occur. If control unit30B determines, based on the voltage level of the rectified DC voltage, that an overvoltage condition is occurring or is likely to occur, control unit30B may alter the control pattern of switches30and32to prevent the overvoltage from damaging rectifier34. In other words, rather than rely on other types of overvoltage protections (e.g., expensive high-voltage external clamping capacitors, and the like) control unit30B of power converter4B can sense the rectified voltage at link12, determine whether the rectified voltage indicates an overvoltage condition, and in case of an overvoltage condition, control unit30B may use a modified control mode to configure rectifier34such that the rectified voltage level is reduced. In this way, the combination of voltage sense unit38and the operations performed by control unit30B act similar to an active clamp structure at the output of rectifier34that senses the rectified voltage and clamps the rectified voltage to levels that the components of rectifier34can tolerate.

For example, control unit30B may receive information from voltage sense unit38about the voltage level associated with the rectified voltage output at link12. Control unit30B may compare the information to one or more thresholds (e.g., a maximum voltage threshold, such as the breakthrough voltage associated with switches20and22) for determining whether an overvoltage condition is occurring or is about to occur at rectifier34. For instance, if the information received from voltage sense unit38indicates that the level of the rectified voltage is meets or exceeds the one or more thresholds (e.g., a voltage value within a tolerance of the break through voltage associated with one or more of switches20and22) control unit30B may determine that an overvoltage condition is occurring at rectifier34.

If control unit30B determines that rectifier34is experiencing or is about to undergo an overvoltage condition, control unit30B may alter the control of switches20and22and control switches20and22via commands across link16to cause rectifier34to operate in “protection mode.” When control unit30B causes rectifier34to operate in protection mode, control unit30B may switch-off, turn-off, or otherwise partially or completely disable switches20A and20B of rectifier34(e.g., each of the high-side switches of rectifier34) while switching-on, turning-on, or otherwise partially or completely enabling switches22A and22B of rectifier34(e.g., each of the low-side switches of rectifier34).

As a result of configuring rectifier34to operate in protection mode during an overvoltage event, control unit30B may cause a low-ohmic connection between nodes18A and18B (e.g., the AC inputs of rectifier34) and a common ground. The low-ohmic connection between nodes18A and18B and a common ground may remove or at least limit any stress that switches20and22may experiencing during an overvoltage and may prevent damage or destruction of rectifier34.

By relying on a rectified output voltage at link12in controlling the operational state of switches20and22, control unit30B can prevent rectifier34from overvoltage conditions that may otherwise damage rectifier34. In this way, rectifier34has protection from overvoltage conditions without the use of expensive external components, such as voltage clamps26A and26B used by power converter4A ofFIG. 2. Through control of rectifier34according to the circuits and techniques of this disclosure, power converter4B may be less expensive and or smaller in size than some other power converters that rely on external protection components, such as high-voltage capacitors.

FIGS. 4A-4Dare block diagrams illustrating alternative examples of rectifier34of the power converter shown inFIG. 3. For example, rectifiers34A,34B,34C, and34D ofFIGS. 4A, 4B, 4C, and 4Ceach illustrate alternative examples of rectifiers that can be controlled according to the level a rectified voltage output to prevent damage during an overvoltage condition.

The respective inputs to rectifiers34A,34B,34C, and34D are each coupled to RX coil32of power converter4B at nodes18A and18B. The respective outputs of rectifiers34A,34B,34C, and34D are each coupled to link12.

Rectifiers34illustrate alternative arrangements of active and/or passive switching elements that can be configured by control unit30B to operate in protection mode described above. In each example of rectifiers34A,34B,34C, and34D, the low-side switches22are capable of operating in active and passive mode via a body diode. The high-side switches may or may not be actively controllable devices. For example, rectifier34A includes high-side diodes52A and52B in a H-bridge configuration with low-side switches22. Rectifier34B includes high-side switch20A and low-side switch22in a half-bridge arrangement to provide a rectified voltage output at link12. Rectifier34C includes high-side diode52A coupled to low-side switch22A to provide a rectified voltage output at link12.

Rectifier34D includes high-side diodes52A and52B in a H-bridge configuration with low-side switches22along with respective switches54A and54B arranged in parallel to each of low-side switches22. In this way, rectifier34D allows switches22to remain active or inactive regardless of whether an overvoltage condition exists at link12and controller unit30B can control switches54A and54B via commands over links16to shunt current away from the input to rectifier34D in case of an over voltage condition. Switches54A and54B may be smaller or less robust switches than switches22and any high-side switches of rectifier34D. Switches54A and54B can be used as shown or in any other arrangement of rectifier, such as rectifiers34A,34B,34C ofFIGS. 4A-4Cas well as rectifier34ofFIG. 3.

FIG. 4A-4Dillustrate that in some examples, perform overvoltage protection in accordance with the circuits and techniques described herein, rectifier34A, rectifier34B, rectifier34C, and rectifier34D may each include at least one low-side element that is a MOS transistor type switch (e.g., switch22A). In some examples, as shown in rectifier34B ofFIG. 4B, at least one high-side element is a MOS transistor type switch (e.g., switch20A). Still in other examples, as shown in rectifiers34A and34C, at least one high-side element is a diode (e.g., diode52A).FIG. 4Aillustrates that in some examples, the at least one low-side element of rectifier34A and the at least one high-side element of rectifier34A are arranged in an H-bridge configuration.FIGS. 4B-4Ceach illustrate that in some examples, the at least one low-side element of rectifiers34B and34C and the at least one high-side elements of rectifier34B and34C are arranged in a H-bridge configuration.FIG. 4Dshows that additional switching elements can be used to shunt current from an input of a rectifier.FIGS. 4A-4Dfurther illustrate that no matter the quantity of switching elements, each of the one or more switching elements that the rectifier uses to rectify the output at link12includes a respective body diode.

FIG. 5is a flowchart illustrating example operations of an example power converter which has overvoltage protection in accordance with one or more aspects of the present disclosure.FIG. 5is described below within the context ofFIG. 3. For example, control unit30B may perform the operations described below with respect toFIG. 5.

In the example ofFIG. 5, a control unit may detect a voltage level of a DC output from a rectifier that receives an AC input (100). For example, control unit30B of power converter4B may receive information from voltage sense unit38as rectifier34outputs a rectified DC voltage at link12.

In the example ofFIG. 5, the control unit may determine whether the voltage level whether the voltage level indicates an overvoltage condition at the rectifier (110). For example, control unit30B may compare the voltage level of the DC output at link12to a threshold or reference voltage received by control unit30B to determine whether or not the voltage at the output of rectifier34is at or reaching levels that could damage rectifier34. For instance, control unit30B may compare the voltage level at link12to a breakthrough voltage associated with one or more of switches20and22to assess whether the DC output is at a voltage level that may damage rectifier34.

In the example ofFIG. 5, if the voltage level if the voltage level of the DC output does not indicate the overvoltage condition (120), the control unit may rectify, with the rectifier, the DC output (130). In other words, control unit30B may rectify the AC input at rectifier34or at least not adjust the state of switches20and22if the level of voltage at the output of rectifier34poses no threat to damaging power converter4B. However, if the voltage level of the DC output does indicate the overvoltage condition (120), the control unit may cause the rectifier to shunt or divert current from the AC input, with the rectifier (140). For example, control unit30B may provide control commands or signals across links16that cause each of high-side switches20to open, turn-off, switch-off, or otherwise become disabled, and further cause each of low-side switches22to close, turn-on, switch-on, or otherwise become enabled. With each of the low-side switches22enabled and each of the high-side switches20disabled, the current at the AC input to rectifier34may be diverted away from the AC input and to ground. In some examples, control unit30B may cause rectifier34to cease rectifying the DC output at link12when causing current to be shunted away from the input to rectifier34.

In some examples, in case of an overvoltage condition, control unit30B may first trigger a “smooth” shunting of current at the input of rectifier34to towards ground. To perform smooth shunting of current, control unit30B may fully turn-on or fully enable low-side switches22(e.g., to cease rectifying a voltage at link12). In some examples, control unit30B may only partially turn-on or turn-on only some of low-side switches22to allow rectifier34to continue to rectify an output at link12, but to reduce the voltage level to prevent damage. In some examples, additional smaller switches may be connected in parallel to low-side switches22and control unit30B may close the additional switches while keeping the main rectifier switches22active in order to reduce the voltage level at link12.

In some examples, when enabling the low-side switches of the rectifier during an overvoltage condition, the control unit may enable the low-side switching elements by performing hard switching. For example, control unit30B may issue one or more commands or signals across links16that cause switches22to be switched on in such a way as to maximize the amount of current that gets diverted from the AC input to rectifier34at a time. In other words, by performing hard switching, control unit30B may cause switches22to switch-on to maximize a rate at which each of low-side switches33shunts the current from the AC input.

In some examples, when enabling the low-side switches of the rectifier during an overvoltage condition, the control unit may enable the low-side switching elements by performing soft switching. For example, control unit30B may issue one or more commands or signals across links16that cause switches22to be switched on in such a way as to maximize efficiency of rectifier34and power converter4B. In other words, control unit30B may control low-side switches22in such a way as to control a rate at which low-side switches22shunt current from the AC input to rectifier34. Examples of soft switching include zero voltage switching techniques and zero current switching techniques. By performing soft switching, control unit30B may be controlling the on-resistance RDSONof each of low-side switches22to minimize the risk that the overvoltage condition will cause damage to rectifier34without inhibiting performance or efficiency of power converter4B.

FIG. 6is a timing diagram illustrating electrical timing characteristics an example power converter which has overvoltage protection in accordance with one or more aspects of the present disclosure. For example,FIG. 6shows timing characteristics of power converter4B. Plot200shows the gate voltage being applied to switches22by control unit30B between times t0and t8. Plot200illustrates that when the gate voltage at links16coupled to switches22reaches the level VON, switches22are switched-on, and when the gate voltage at links16coupled to switches22falls to the level VOFF, switches22are switched-off.

Plot202shows the rectified voltage level of the DC output of rectifier34between times t0and t8. Plot202shows that the threshold voltage VTH, control unit gate voltage being applied to switches22by control unit30B between times t0and t8. Plot202shows that when the voltage level at the output of rectifier34meets or exceeds the threshold voltage VTH, control unit30B may cause switches22to close, which further causes the voltage level at the output of rectifier34to drop.

In some examples, if switches20and22are 12V devices (e.g., devices with operating limits not to exceed 12V), a voltage picked up by RX coil32may easily exceed 20-30V. Control unit30B may include a comparator that compares the voltage at the output of rectifier34to a threshold that corresponds to the operating limit 12V. When the rectified voltage at the output of rectifier34exceeds the predefined threshold (e.g. 12V), control unit30B may cause rectifier34to operate in protection mode. In other words, control unit30B may cause both low-side switches22to be activated, switched-on, or otherwise enabled, shunting AC current from nodes18A and18B to ground and steering current away from power converter4B. In addition, control unit30B may cause high-side switches20to be switched-off turned-off, or otherwise disabled. Control unit30B may cause rectifier34to transition out of protection mode when the rectified voltage at the output of rectifier34drops below the hysteresis window (e.g., VSAFE). Plot2shows the rectified output of rectifier34.

FIG. 7is a block diagram of an example wireless power receiver with a passive rectifier. The passive rectifier ofFIG. 7may receive an AC input at receiving coil circuit150which includes LS, CS, and CDand convert the AC input using passive rectifier152to a rectified DC voltage output at buck converter154(e.g., a step-down converter) at VR. Passive rectifier152includes four diodes arranged in an H-bridge configuration for performing passive rectification.

FIGS. 8A and 8Bare circuit diagrams of an example wireless power receiver with a synchronous rectifier and voltage clamps for overvoltage protection.FIG. 8Bshows a more detailed view of a portion ofFIG. 8A. Dotted portion300highlights the similar features of the two circuit diagrams.FIGS. 8A and 8Bare circuit diagram equivalents of power converter4A ofFIG. 2and rely on expensive voltage clamps to protect the rectifier from overvoltage conditions.

FIG. 9is a timing diagram illustrating electrical timing characteristics the example power wireless power receiver ofFIG. 8. When compared to the timing diagram ofFIG. 6,FIG. 9shows that the rectified voltage of a power converter that relies on expensive voltage clamps, such as those shown inFIG. 3, may have similar voltage and timing characteristics at the output of the rectifier, as a power converter that operates according to the techniques and circuits described herein. In other words, a power converter, such as power converter4B, that operates according to the techniques and circuits described herein may be protected from overvoltage without relying on expensive voltage clamps and the like, and without degrading performance.

Clause 1. A circuit comprising: a rectifier configured to rectify a DC output from an AC input; a sensing unit configured to detect a voltage level of the DC output; a control unit configured to control the rectifier based on the voltage level of the DC output by at least controlling the rectifier to: rectify the DC output from the AC input if the voltage level of the DC output does not indicate an overvoltage condition at the circuit; and shunt current from the AC input if the voltage level of the DC output does indicate the overvoltage condition.

Clause 2. The circuit of clause 1, wherein the rectifier comprises at least one low-side element and at least one high-side element, wherein the control unit is configured to control the rectifier to shunt the current from the AC input if the voltage level of the DC output does indicate the overvoltage condition by at least enabling the at least one low-side element.

Clause 3. The circuit of clause 2, wherein the control unit is configured to control the rectifier to further shunt the current from the AC input if the voltage level of the DC output does indicate the overvoltage condition by at least disabling the at least one high-side element.

Clause 4. The circuit of any of clauses 2-3, wherein the control unit is configured to enable the at least one low-side element by at least performing hard switching of the at least one low-side element to maximize a rate at which the at least one low-side element shunts the current from the AC input.

Clause 5. The circuit of any of clauses 2-4, wherein the control unit is configured to enable the at least one low-side element by at least performing soft switching of the at least one low-side element to control a rate at which the at least one low-side element shunts the current from the AC input.

Clause 6. The circuit of any of clauses 2-5, wherein the at least one low-side element is a MOS transistor type switch.

Clause 7. The circuit of any of clauses 2-6, wherein the at least one high-side element is a MOS transistor type switch or a diode.

Clause 8. The circuit of any of clauses 2-7, wherein the at least one low-side element and the at least one high-side element are arranged in a half-bridge or a H-bridge configuration.

Clause 9. The circuit of any of clauses 2-8, wherein the rectifier comprises a plurality of low-side elements including the at least one low-side element, wherein the control unit is configured to enable the at least one low-side element by enabling the at least one low-side element without enabling at least one other low-side element of the plurality of low-side elements.

Clause 10. The circuit of any of clauses 2-9, wherein the rectifier comprises a plurality of low-side elements including the at least one low-side element, wherein the control unit is configured to enable the at least one low-side element by enabling each of the plurality of low-side elements.

Clause 11. The circuit of any of clauses 1-10, wherein the rectifier comprises at least one low-side element, at least one high-side element, and at least one switching element arranged in parallel to the at least one low-side element, wherein the control unit is configured to control the rectifier to shunt the current from the AC input if the voltage level of the DC output does indicate the overvoltage condition by at least enabling the at least one switching element without changing whether the at least one low-side element is enabled or disabled.

Clause 12. The circuit of any of clauses 1-12, wherein the rectifier comprises one or more switching elements, wherein each of the one or more switching elements of the rectifier comprises a respective body diode.

Clause 13. The circuit of any of clauses 1-13, wherein the control unit is further configured to: compare the voltage level of the DC output to a threshold voltage; and determine whether the voltage level of the DC output indicates the overvoltage condition at the circuit based on the comparison between the voltage level and the threshold voltage.

Clause 14. A method comprising: detecting a voltage level of a DC output from a rectifier that receives an AC input; determining, by a control unit, whether the voltage level indicates an overvoltage condition at the rectifier; rectifying, with the rectifier, the DC output if the voltage level of the DC output does not indicate the overvoltage condition; and shunting current from the AC input, with the rectifier, if the voltage level of the DC output does indicate the overvoltage condition.

Clause 15. The method of clause 14, wherein the rectifier comprises at least one low-side element and at least one high-side element, wherein shunting current from the AC input comprises enabling the at least one low-side element.

Clause 16. The method of clause 15, wherein shunting current from the AC input further comprises disabling the at least one high-side element

Clause 17. The method of any of clauses 14-16, wherein enabling the at least one low-side element comprises hard switching, by the control unit, the at least one low-side element of the rectifier to maximize a rate at which the at least one low-side element shunts the current from the AC input.

Clause 18. The method of any of clauses 14-17, wherein enabling the at least one low-side element comprises soft switching, by the control unit, the at least one low-side element of the rectifier to control a rate at which the at least one low-side element shunts the current from the AC input.

Clause 19. The method of clause 14, further comprising: comparing, by the control unit, the voltage level of the DC output to a threshold voltage; and determining, by the control unit, whether the voltage level of the DC output indicates the overvoltage condition based on the comparison between the voltage level and the threshold voltage.

Clause 20. A circuit comprising: means for detecting a voltage level of a DC output from a rectifier that receives an AC input; means for determining whether the voltage level indicates an overvoltage condition at the rectifier; means for rectifying the DC output if the voltage level of the DC output does not indicate the overvoltage condition; and means for shunting current from the AC input if the voltage level of the DC output does indicate the overvoltage condition.