Method and device to operate a power switch in multiple modes

Methods and circuits are provided for controlling an electronic switch such that it may be controlled by an external control signal, such as a PWM signal, or be set to operate in an active-diode mode, wherein current is allowed to flow through the switch in only one direction. The described circuits are configured to autonomously control the electronic switch, such that no external control signal is required when the active-diode mode is used. The provided techniques allow electronic switches to be efficiently used as part of a power stage or part of an active rectifier, so as to support bi-directional switched-mode power supplies, motor/generator drivers, and related electric circuits that require bi-directional power flow. By reusing electronic switches thusly and implementing an active-diode mode, the circuitry is minimized while maintaining good power efficiency.

TECHNICAL FIELD

The present application relates to circuits and methods for controlling a power switch and, more particularly, provides techniques in which the conductivity of the power switch may be determined, in a first mode, by a switch control signal and, in a second mode such as an active-diode mode, by a voltage or current of the power switch.

BACKGROUND

Electronic switches are widely used in a variety of applications. In many of these applications, the electronic switches are operated primarily in either a fully on mode or in an off mode. The state wherein a switch is partially on, which may be termed linear or triode mode for some switch types, is avoided, as the power loss during such a state is higher than the loss in the fully on state or in the off state. Common applications that use electronic switches primarily in a fully on or off mode include switched-mode power supplies (SMPSs), electric motor drivers, and charging circuits.

An example of an electronic switch that is commonly used in a fully on or in an off state is the metal-oxide semiconductor field-effect transistor (MOSFET). MOSFETs represent a type of switch that has an intrinsic diode, such that the switch is not capable of blocking current in one direction. When a MOSFET is turned off, e.g., by appropriate setting of the gate voltage applied to the MOSFET, current flow is blocked in one direction, but the intrinsic (body) diode allows current flow in the other direction, provided that the voltage across the intrinsic diode is high enough to forward bias the diode. In many applications that do not require current blocking in both directions through a switch, the intrinsic diode provides a useful property or is at least not harmful.

The electronic switches of an SMPS may be used both in a power stage circuit of the SMPS and in an active rectifier circuit, and the switch control required for these circuits is quite different. Consider, for example, an isolated SMPS wherein a transformer separates primary and secondary sides. Electronic switches within a power stage on the primary side may be switched (controlled) so as to appropriately transfer power from an input to the transformer and, in turn, to the secondary side and an output of the SMPS. The power stage converts a direct-current (DC) voltage into an alternating-current (AC) voltage applied across the transformer. A rectifier converts the AC voltage induced on the secondary side of the transformer into a DC voltage, which is provided at the output. A passive rectifier, e.g., a diode bridge, may be used to provide the DC voltage, but the voltage drop across the diodes leads to power loss that may be unacceptably high in some applications. In particular, SMPSs providing low output voltage, e.g., 3.3V, 1.8V, have very poor efficiency when using diode bridges, as the voltage drop (typically 0.7V) across each diode represents a large portion of the power consumption of the system. The power efficiency of an SMPS may be greatly improved by using electronic switches to perform active rectification, rather than using diode-based passive rectification. The voltage drop across an electronic switch, which is related to the on resistance of the switch, is typically markedly smaller than the voltage drop across a diode, and the resultant power loss incurred by a properly-controlled electronic switch is significantly smaller than the power loss of a diode.

An active rectifier replaces the diodes of a passive rectifier with electronic switches. The switches must be controlled such that current flow is only allowed in one direction which, for a MOSFET, must be in the direction of the intrinsic diode. Meanwhile, the electronic switches of the power stage are controlled in an entirely different manner. In particular, a duty cycle, frequency, and/or phase shift used to control the power stage switches is adjusted, typically, so as to maintain a desired voltage at the output of the SMPS.

A bi-directional SMPS supports a forward power flow from a primary to a secondary side, as described above, and a reverse power flow from the secondary to the primary side. In the reverse direction, a secondary-side power stage must be controlled so as to transfer appropriate energy, whereas the voltage on the primary side must be rectified.

Switch control circuits are desired that are capable of controlling electronic switches in different operational modes, such that an electronic switch may operate to support a power stage or an active rectifier.

SUMMARY

According to an embodiment, a method is provided for controlling a power switch having an intrinsic diode configured to conduct current in a reverse direction of the power switch, wherein the current in the reverse direction cannot be blocked by the power switch. The method comprises receiving a configuration signal indicating an operational mode for the power switch. If an active-diode configuration is indicated, a current and/or voltage of the power switch is sensed and the power switch is turned on if the sensed current and/or voltage indicates positive current in the reverse direction through the power switch. If a normal (PWM) configuration is indicated, the power switch is turned off responsive to receiving a switch control signal directing that the power switch be turned off, and is turned on responsive to receiving a switch control signal directing that the power switch be turned on.

According to an embodiment of a bi-directional switched mode power supply (SMPS), the SMPS comprises first and second SMPS terminals for providing external connections to the SMPS, high and low-side switches, an inductor, a controller, and first and second driver circuits. The high and low-side switches are coupled together at a switching node. The high-side switch is additionally coupled to the first SMPS terminal. The inductor is electrically interposed between the switching node and the second SMPS terminal. The controller is configured to control the power flow between the first and the second SMPS terminals by generating a switch control signal for one of the high-side and the low-side switches. The first driver control circuit is configured to control the high-side switch using an active-diode mode or a normal mode, wherein for the active-diode mode the high-side switch conductivity is based upon a sensed current or voltage of the high-side switch, and for the normal mode the high-side switch conductivity is based upon the switch control signal generated by the controller. Similarly, the second driver control circuit is configured to control the low-side switch using the active-diode mode or the normal mode, wherein for the active-diode mode the low-side switch conductivity is based upon a sensed current or voltage of the low-side switch, and for the normal mode the low-side switch conductivity is based upon the switch control signal provided by the controller. The SMPS is configured to operate, during a first interval, in a first mode in which power is transferred from the first to the second SMPS terminal, and, during a second interval, in a second mode in which power is transferred from the second to the first SMPS terminal.

According to an embodiment of a converter, e.g., a DC/DC or an AC/DC converter, with isolation between the primary side and the secondary side, such as a bi-directional on-board charger (OBC), the converter comprises first and second direct-current (DC) power nodes, each of which is for connecting to a power source or sink, an isolation transformer comprising primary and secondary windings, a primary-side power stage, a secondary-side power stage and a controller. The primary-side power stage couples the first DC power node to the primary winding. The secondary-side power stage couples the secondary winding to the second DC power node. The secondary-side power stage comprises a secondary-side half bridge including first and second secondary-side power switches arranged in a half-bridge configuration. The secondary-side power stage further comprises first and second secondary-side switch controller circuits coupled, respectively, to the first and second secondary-side power switches. Each of the switch controller circuits is configured for operation in a normal mode, in which an externally-provided switch control signal controls conductivity of the power switch coupled to the switch controller circuit, and an active-diode mode, in which conductivity of the power switch coupled to the switch controller is based upon a sensed current and/or voltage of the power switch. The controller is configured to operate the converter, during a first interval, in a forward mode in which power is transferred from the first to the second DC power node, and, during a second interval, in a reverse mode in which power is transferred from the second to the first power node. For the forward mode, the controller sets the secondary-side controller circuits to operate the secondary-side power switches in the active-diode mode. For the reverse mode, the controller sets the secondary-side controller circuits to operate the secondary-side power switches in the normal mode, and generates the externally-provided control signals for the secondary-side power switches.

DETAILED DESCRIPTION

Many electric circuits rely upon electronic switches to generate alternating current (AC) power and/or to rectify AC power in generating direct-current (DC) power. For example, a switched-mode power supply (SMPS), such as a buck or a boost converter, inputs a DC voltage from a power supply, uses a power stage comprised of one or more electronic switches to convert the DC voltage into an AC voltage, and uses a rectifier to convert AC voltage into a DC voltage that is provided at an output. There are numerous circuit topologies for implementing an SMPS, including both isolated and non-isolated voltage converters. Exemplary non-isolated voltage converters include buck and boost converters, and use an inductor as an energy-storage component. Isolated voltage converters including, e.g., flyback and forward converters, use a transformer both for energy storage/transfer and to provide electrical (galvanic) isolation between the input and the output of the converter. While the aforementioned converters vary in their specific circuit topologies, they are similar in that each has a circuit that may be considered a power stage and a circuit that may be considered a rectifier. In a non-isolated buck converter, e.g., a single electronic switch may provide the power stage, whereas a diode may provide the rectifier. In a typical isolated converter, the power stage may be a half bridge that includes two electronic switches, whereas the rectifier may include a diode bridge or similar.

Many modern circuits, including some SMPSs, use active rectification, in which an electronic switch is used to allow current flow in one direction and to block current flow in the other direction, thereby emulating the operation of a diode. Active rectification provides better power efficiency than passive rectification based upon diodes, as the power loss incurred by the voltage drop across the diode may be greatly reduced. However, active rectification requires the generation of control signals for one or more electronic switches such that current is only allowed to flow in the desired direction. The voltage across an electronic switch may be used to determine when the switch should be turned on. For example, a typical enhancement-mode n-channel MOSFET includes a body diode in the direction from the source terminal to the drain terminal of the MOSFET. If the source voltage is greater than the drain voltage, the switch should be turned on so that positive current will flow from the source to the drain of the MOSFET, without requiring use of the body diode and its associated power loss. When the drain voltage is greater than the source voltage, the switch should be turned off, so as to block positive current from flowing from the drain to the source. Additionally or alternatively, a current flow through the switch may be monitored or predicted in other ways, e.g., using the voltage across a shunt resistor, a sensing path of a power switch (wherein part of the switch area is used as sensing element, KILIS) or by measuring the voltage across an inductor or winding that is connected in series with the switch. Dedicated active-diode control circuitry may measure a voltage or current of the switch, and control conductivity of the switch based upon such measurements. The combination of such control circuitry and an electronic switch effectively provides an autonomous active diode, e.g., no external control signal is required for controlling the electronic switch.

In contrast to the electronic switches of an active rectifier, the electronic switches of a power stage are controlled based on externally-provided control signals. In a typical SMPS, a controller, such as a proportional-integral-derivative (PID) controller, generates control signals for one or more electronic switches of a power stage so as to maintain a desired voltage at the output of the SMPS.

An isolated SMPS providing a step-down or a step-up voltage conversion has a primary-side power stage comprised of electronic switches that are controlled by externally-provided control signals, e.g., from a controller operable to regulate an output voltage on the secondary side. Such an SMPS may also have a secondary-side active rectifier comprised of electronic switches operating as autonomous active diodes. In a first mode, power is transferred from the primary to the secondary side, and the output voltage is stepped down or up relative to the input. If the SMPS is bi-directional, the SMPS should also be able to operate in a second mode in which power is transferred from the secondary to the primary side, so as to step-up or step-down a secondary-side input voltage and provide the stepped-up or stepped-down voltage at a primary-side output. In preferred embodiments, the primary-side electronic switches are controlled by the externally-provided control signals in the first operational mode (primary-to-secondary power transfer), and are operated as active diodes in the second operation mode (secondary-to-primary power transfer). Conversely, the secondary-side electronic switches are preferably operated as active diodes in the first operational mode (primary-to-secondary power transfer), and are controlled by externally-provided control signals in the second operational mode (secondary-to-primary power transfer).

Described herein are circuits and methods for controlling electronic switches in multiple modes including, e.g., an active-diode mode and an externally-controlled mode. For safety-critical applications, the switch control may also include protection modes, in which the active-diode operation or externally-controlled operation may be overridden responsive to detection of faults such as a short-circuit or over-current condition. These circuits and methods find particular use in bi-directional SMPSs, wherein one or more electronic switches may be externally-controlled so as to provide a power stage, or may be set to an active-diode mode to provide rectification. While the circuits and methods are described primarily in the context of SMPSs, other devices may also advantageously use these circuits and methods. For example, the electronic switches of a bridge circuit may be actively controlled in a motor mode to set a direction and/or speed of an electric motor/generator. In a generator mode, the electronic switches of the bridge circuit may be set to an active-diode mode, so as to provide active rectification when the motor/generator is operating in a generation mode.

For clarity of explanation, the inventions are described by way of particular exemplary embodiments. It should be understood that the below examples are not meant to be limiting. Circuits and techniques that are well-known in the art are not described in detail, so as to avoid obscuring unique aspects of the invention. Features and aspects from the example embodiments may be combined or re-arranged, except where the context does not allow this.

The description begins with an embodiment of a non-isolated bidirectional buck/boost converter that is configured to operate in a first mode, in which power is transferred in a forward direction, and a second mode, in which power is transferred in a reverse direction. Electronic switches within this buck/boost converter are operated in an active-diode, externally-controlled, or protected mode. The buck/boost converter description is followed by more detailed descriptions of gate drive control circuitry used in providing the different operational modes, and which may be used by the buck/boost converter or by other applications. Next, use of the gate driver control circuitry for motor/generator control is described. In another example, an isolated on-board charger is described, wherein each of a primary and secondary set of electronic switches may be operated in an active-diode or an externally-controlled mode. Finally, a method for controlling a power switch in an active-diode or externally-controlled mode is described.

Buck-Boost Converter with Safety Protection Switches

FIG. 1illustrates a non-isolated bi-directional voltage converter100that may be operated in either a buck or a boost mode, and first and second batteries BAT1, BAT2connected to the voltage converter100. Depending upon the power flow direction, each battery may operate as either a power source or as a power sink (load). As illustrated, the first battery BAT1has a first voltage V1that is higher than the voltage V2of the second battery. For example, the first battery BAT1may have a nominal voltage of 48V, whereas the second battery BAT2has a nominal voltage of 12V. The voltage converter100, as illustrated inFIG. 1, may be used to transfer energy between two energy sources for, e.g., an automotive application, in either direction. When energy is transferred from the first battery BAT1to the second battery BAT2, the voltage converter100operates in a buck (step-down) mode and the second battery BAT2is charged. When energy is transferred in the opposite direction, the voltage converter100operates in a boost (step-up) mode, so as to charge the first battery BAT1. Hence, the voltage converter100is a type of buck-boost converter.

The voltage converter100comprises a first terminal102for connection to an external power source/sink, such as the first battery BAT1, and a second terminal104for connection to another external power source/sink, such as the second battery BAT2. In addition to the illustrated batteries BAT1, BAT2, additional power source/sinks, such as motors or generators, may also be connected to the terminals102,104of the voltage converter100, e.g., in parallel to the batteries BAT1, BAT2. The voltage converter100includes a high-side switch TH, a high-side gate driver112H for driving said switch TH, and a high-side gate drive controller120H for controlling the gate driver112H, which together comprise a high-side switch circuit110H. The components of the high-side switch circuit110H may be monolithically integrated. The voltage converter100includes a similar low-side switch circuit110L, which includes a low-side switch TL, a low-side gate driver112L, and a low-side gate drive controller120L. The voltage converter100additionally includes an inductor L1and may optionally include a protection isolator circuit150. The protection circuit150includes protection switches T1, T2, which are driven by respective gate drivers152,154. The protection circuit150is included for safety-critical applications, including automotive applications, and may be used to isolate the batteries BAT1, BAT2from each other or from ground in case of, e.g., a short fault across one of the switches TH, TL.

As compared with prior voltage converter control, the high-side and low-side gate-drive controllers120H,120L enable the voltage converter100to control an associated switch in one of several modes and, thereby, allow each of the switch circuits110H,110L to be operated in multiple modes, including a pulse-width-modulated (PWM) mode and an active-diode mode, as indicated by the mode signals MODE1, MODE2. Additionally, the mode signals may indicate safety cutoff modes, wherein a switch should be turned off responsive to an external or internal indication of a fault. The different modes will be explained more thoroughly further below in conjunction with the descriptions ofFIGS. 2A, 2B, 3A, and 3B.

The voltage converter100further includes a controller190, which generates control signals for the gate-drive controllers120H,120L and the protection circuit150. A first mode signal MODE1generated by the controller190indicates whether the high-side gate drive controller120H should operate in a PWM mode, an active-diode mode, or otherwise. When the first mode signal MODE1indicates the PWM mode, a first PWM signal PWM1generated by the controller190controls conductivity of the high-side switch TH, via the gate driver112H. For example, a PID controller within the controller190may generate the first PWM signal PWM1to maintain a desired target voltage across the battery BAT2. When the first mode signal MODE1indicates active-diode mode, the signal PWM1is ignored by the high-side GD controller120H, and conductivity of the high-side switch TH is based upon the current ITHthrough the high-side switch TH, a drain-source voltage VDS_THof the high-side switch TH, or a similar signal of the high-side switch circuit110H. In this way, the high-side switch circuit110H may operate autonomously in the active-diode mode, without relying on PWM control signals from the controller190. In this mode, the controller190does not need to generate a control signal PWM1and does not need to sense currents or voltages of the high-side switch TH to do so. In addition to relieving the controller190from generating the first PWM control signal PWM1, delays in sensing currents or voltages by controller190may be eliminated or, at least, reduced.

Corresponding mode and PWM signals MODE2, PWM2similarly configure and control the low-side GD controller120L. The safety switches T1, T2of the protection circuit150are turned on by the safety control signal CTRL_SAFETY, which is generated by the controller190. If the controller detects a fault in the voltage converter100, e.g., excessive current flow from one of the batteries BAT1, BAT2or a battery voltage V1, V2outside of a normal (non-fault) range, the controller190turns off the safety switches T1, T2using the safety control signal CTRL_SAFETY.

The controller190and its constituent parts may be implemented using a combination of analog hardware components (such as transistors, amplifiers, diodes, resistors, analog-to-digital converters), and processor circuitry that includes primarily digital components. The processor circuitry may include one or more of a digital signal processor (DSP), a general-purpose processor, and an application-specific integrated circuit (ASIC). The controller190may also include memory, e.g., non-volatile memory such as flash, that includes instructions or data for use by the processor circuitry, and one or more timers. The controller190inputs sensor signals such as signals corresponding to the battery voltages V1, V2, and the current I1of the inductor L1.

The high and low-side switches TH, TL illustrated inFIG. 1are enhancement-mode metal-oxide semiconductor field-effect transistors (MOSFETs), but other switch types may be used. For example, junction field-effect transistors (JFETs), bipolar junction transistors (BJTs), insulated gate bipolar transistors (IGBTs), high electron mobility transistors (HEMTs), or other types of power transistors may be preferred in some applications. Note that not all of these switch types have intrinsic diodes. The power switches described in the embodiments that follow are also illustrated as MOSFETs, but may be replaced with other switch types.

FIG. 2Aprovides a schematic diagram200corresponding to the voltage converter100ofFIG. 1, when the voltage converter100is operated in a buck mode of operation.FIG. 2Billustrates waveforms corresponding to the buck-mode operation of this voltage converter. The illustrated voltage converter200inputs power from the battery BAT1, having a voltage of 48V, and outputs power to (charges) the battery BAT2, having a voltage of 12V. The controller190, which is not shown for ease of illustration, generates signals MODE1, MODE2, and PWM1for controlling the high and low-side switch circuits110H,110L.

The mode signal for the high-side switch circuit110H is set to PWM_MODE, so that the high-side switch TH is controlled by the control signal PWM1. The low-side mode signal is set to ACTIVE_DIODE_MODE, thereby setting the low-side switch circuit110L to only allow positive current flow in the illustrated direction IFW. The low-side switch TL is illustrated as a free wheeling diode, but it should be understood that this is accomplished by internally controlling, within the low-side switch circuit110L, the switch TL to be turned on when the low-side switch TL would otherwise have current flow through its body diode. The controller190need not generate the switch control signal PWM2for the low-side switch TL; the low-side switch circuit110L operates autonomously based upon internally-sensed voltage(s) and/or current(s).

A positive current IPflows through the high-side switch TH and the inductor L1when the high-side switch TH is turned on. A positive current IFWflows through the low-side switch TL and the inductor L1when the low-side switch TL is turned on. Both of these currents IP, IFWflow through the inductor IL, and correspond to the inductor current IL.

FIG. 2Billustrates a waveform204for the high-side control signal PWM1and a waveform202for the inductor current IL. During positive intervals, denoted ‘P,’ the control signal PWM1turns on the high-side switch TH, via the high-side GD controller120H, thereby leading to an increase in the inductor current IL. Each positive interval is followed by a freewheeling interval, denoted ‘F,’ during which the inductor current ILdecreases. The rate at which the current ILrises or falls during these intervals P, F is determined by the voltage difference across the inductor L1, i.e., V1-V2if voltage drops across the switches are ignored, and the inductance of the inductor L1. If the current ILduring a freewheeling interval falls to zero, a zero interval, denoted ‘Z,’ follows the freewheeling interval and the voltage converter200operates in discontinuous conduction mode (DCM). If the high-side control signal PWM1is always activated again before the current ILfalls to zero during each of the freewheeling intervals or if the current ILis allowed to become negative, the voltage converter200operates in continuous conduction mode (CCM). DCM provides power-saving advantages for converters that often operate in low-power modes, whereas CCM provides simpler control for some topologies.

FIG. 3Aprovides a schematic diagram300of a voltage converter operating in a boost mode of operation, i.e., where power flows from the second battery BAT2to the first battery BAT1.FIG. 3Billustrates waveforms corresponding to the boost-mode operation of this voltage converter. The controller190, which is not shown for ease of illustration, generates signals MODE1, MODE2, and PWM2for controlling the high and low-side switch circuits110H,110L. Positive current IBOOSTflows in the illustrated direction, which is opposite to the direction ILshown inFIG. 2A.

The mode signal for the low-side switch circuit110L is set to PWM_MODE, so that the low-side switch TL is controlled by the control signal PWM2. The high-side mode signal is set to ACTIVE_DIODE_MODE, thereby setting the high-side switch circuit110H to only allow positive current flow in the illustrated direction IFW. The high-side switch TH is illustrated as a freewheeling diode, but it should be understood that this is accomplished by internally controlling the switch TH to be turned on when the high-side switch TH would otherwise have current flow through its body diode. The controller190need not generate the switch control signal PWM1for the high-side switch TH; the high-side switch circuit110H operates autonomously based upon internally sensed voltage(s) and/or current(s).

A positive current IPflows through the inductor L1and the low-side switch TL when the low-side switch TL is turned on. A positive current IFWflows through the inductor L1and the high-side switch TH when the high-side switch TH is turned on. Both of these currents IP, IFWflow through the inductor IL, and correspond to the boost current IBOOST.

FIG. 3Billustrates a waveform304for the low-side control signal PWM2and a waveform302for the boost current IBOOST. During positive intervals, denoted ‘P,’ the control signal PWM2turns on the low-side switch TL, via the low-side GD controller120L, thereby leading to an increase in the boost current IBOOST. Each positive interval P is followed by a freewheeling interval, denoted ‘F,’ during which the boost current IBOOSTdecreases. As in the buck operation described above, if the current IBOOSTduring a freewheeling interval falls to zero, a zero interval ‘Z’ follows the freewheeling interval and the voltage converter300operates in discontinuous conduction mode (DCM), as illustrated.

FIG. 4illustrates a schematic diagram400for an alternative configuration of a buck-boost converter. This voltage converter400is similar to the converter100ofFIG. 1, but the active rectification is provided by the safety circuit450rather than the high or low-side switches TH, TL.

The high and low-side switches TH, TL and their respective gate drivers412H,412L are arranged in a half-bridge configuration. An inverter430is configured such that the low-side switch TL is turned on whenever the high-side switch TH is turned off, and vice-versa. (Additionally, a brief dead-time during which neither switch is turned on is typically included at switch transitions to avoid shoot-through. For ease of illustration, circuitry to implement such dead-time intervals is not explicitly shown.) This arrangement avoids use of the high and low-side GD controllers110L,110H, thereby simplifying the power stage. A controller controls the switches TH, TL using a single PWM control signal for either buck or boost mode. Without some other rectification, this arrangement leads to CCM, which may lead to undesired current flows in some situations.

To address this problem, the safety circuit450is configured to also provide active rectification. In addition to the safety switches T1, T2and their respective drivers452,454, the safety circuit450includes a GD1 controller461and a GD2 controller462. These controllers461,462are configured similarly to the controllers120L,120H ofFIG. 1. Notably, each of the GD controllers461,462may be operated in multiple modes, including a direct-control mode, which is similar to the PWM mode described for controller110H,110L, and an active-diode mode. The mode signals MODE1, MODE2determine the mode (e.g., direct-control or active-diode mode) for the GD controllers461,462, whereas the control inputs CTRL1, CTRL2determine the conductivity of the switches T1, T2when the mode is set to the direct-control mode. The mode and control signals MODE1, MODE2, CTRL1, CTRL2are typically generated by a controller, such as the controller190described previously. For ease of illustration, such a controller is not shown.

When the first mode signal MODE1is set to the active-diode mode, conductivity of the first switch T1is controlled such that the switch T1is turned on whenever current would otherwise flow through the body diode of the switch T1. For the illustrated MOSFET, this corresponds to a current flowing from the source terminal to the drain terminal of the switch T1. Such operation requires no external intervention, e.g., generation of a switch control signal from a controller. In the active-diode mode, the first switch circuit, which is comprised of the first switch T1, the first gate driver452, and the GD1 controller461, operates autonomously to provide active-diode functionality. Note that the mode may also be set without providing the dedicated mode control signal MODE1as indicated, e.g., the mode may be stored within a configuration register of the GD1 controller461. GD2 controller462, the second gate driver454, and the second safety switch T2operate in a manner similar to that described above.

FIG. 5illustrates a schematic diagram500corresponding to the voltage converter400ofFIG. 4, when the voltage converter400is operated in a buck mode of operation. For the GD1 controller461, the first mode MODE1is set to the direct-control mode, and the first control input CTRL1is set to ON such that the first switch T1conducts. The mode MODE2of the GD2 controller462is set to the active-diode mode, in which the second control input CTRL2is not used. In this mode, the GD2 controller462uses a voltage or current of the second switch T2to turn on the second switch T2whenever there is a potential current flow in the direction from the switch source terminal to the switch drain terminal, i.e., in the direction of positive current flow IL. The GD2 controller462senses a current, e.g., IL, or a voltage, e.g., the drain-source voltage VT2_DS, of the second safety switch T2to determine when to turn on the second safety switch T2, so as to only allow current flow in the desired direction, i.e., towards the second battery BAT2. Such operation allows DCM, and its associated power-saving advantages during periods of low power transfers, when using a conventional half bridge and relatively simple control for the power stage. The resultant PWM control of the half bridge and the inductor current ILare similar to the waveforms204,202illustrated inFIG. 2B.

While not explicitly illustrated, the voltage converter400ofFIG. 4may also be operated in a boost mode by setting the GD1 controller461to the active-diode mode, setting the GD2 controller462to the direct-control mode, and setting the second control input CTRL2to ON. Such operation only allows positive current in the direction from the second terminal104to the first terminal102, i.e., opposite to the illustrated current flow direction IL. Such a configuration also allows DCM while operating the half bridge (TH, TL) in a simple manner, and results in PWM and current waveforms304,302similar to those illustrated inFIG. 3B.

Gate Drive Controller

FIG. 6Aillustrates a gate-drive controller620, as could be used for any of the gate-drive controllers120H,120L,461,462described previously in conjunction withFIGS. 1 and 4. The gate-drive controller620provides a control signal CTRL_TPWR for driving a gate driver612which, in turn, drives a power switch TPWR. The power switch TPWRcould be any of the high-side, low-side, or safety switches TH, TL, T1, T2described previously. The gate-drive controller620comprises a gate-drive signal generator622, an active-diode controller624, a fault detector626, a current sensor6282, and a voltage sensor6284.

The active-diode-mode operation is implemented using the active-diode controller624and one or both of the sensors6282,6284. The voltage sensor6284is configured to measure the drain-to-source voltage of the power switch TPWR, and provide the result VDS_TPWRto the active-diode controller624. The current sensor6282is configured to measure a current614of the power transistor TPWR, and to provide the result ITPWRto the active-diode controller624. The current ITPWRmay be sensed, e.g., using a shunt resistor in series with the power switch TPWR, using a DCR circuit, or using the drain-to-source voltage VDS_TPWRof the power transistor TPWR.

In a preferred embodiment, a turn-on trigger6244activates an active-diode control signal AD_CTRL when the drain-to-source voltage VDS_TPWRis below an activation threshold VDS_THR, which is negative. Stated alternatively, the source-to-drain voltage of the power transistor TPWRshould be above a threshold that prevents the body diode from carrying current through the power switch TPWR. For example, the body diode may be forward biased at a source-to-drain voltage of 0.7V, in which case the power switch TPWRshould be turned on if the drain-to-source voltage VDS_TPWRis below, e.g., −0.1V or −0.2V. (Stated alternatively, the source-to-drain voltage is above 0.1V or 0.2V.)

In the active-diode mode, the power switch TPWRis preferably turned off when the current through the switch TPWRis zero, as may be sensed by the current sensor6282. Due to delays of the GD signal generator622and the gate driver612, it may be desirable to trigger the turn off of the power switch TPWRbefore the current magnitude reaches zero. This is done by a turn-off trigger circuit6242of the active-diode controller624, which compares the sensed current ITPWRagainst a threshold ITPWR_THR, and deactivates the active-diode control signal AD_CTRL responsive to detecting that the magnitude of this current reaches the magnitude of the threshold current ITPWR_THR. For the illustrated current direction ILOAD, the threshold ITPWR_THRis a small negative value and the switch turn off is triggered when ILOAD>ITPWR_THR, wherein the current ILOADis negative when current flows in the direction of the body diode of the power switch TPWR.

In preferred embodiments, the body diode does not carry any current. If the power switch is turned off too soon, the body diode may be activated which leads to a sudden change in the drain-to-source voltage of the power switch TPWR. This, in turn, may lead to undesired electromagnetic interference (EMI). To avoid such problems, the current threshold ITPWR_THRmay be set such that the switch TPWRis not turned off until the current direction ILOADreverses, and a small level of positive current flows in the illustrated direction of ILOAD.

The above-described active-diode controller624uses the sensed voltage VDS_TPWRto trigger the turn-on of the switch TPWR, and uses the sensed current ITPWRto trigger the turn-off of the switch TPWR. In other embodiments, the sensed voltage VDS_TPWRmay be used to trigger both the turn on and turn off of the power switch TPWR. However, detecting the low voltage levels necessary to accurately turn off the power switch TPWRat near zero current is difficult, so the preferred embodiments use the sensed current ITPWRto trigger the turn off. In yet other embodiments, the sensed current ITPWRmay be used to trigger both the turn on and turn off. For such an embodiment, the turn on requires some current flow in the direction of the body diode to detect sensed current ITPWRin the desired direction. This means that the body diode will be used for at least a brief period of time at each turn on transition, which incurs an unnecessary power loss and, potentially, a high level of EMI. Hence, this technique is not preferred.

The gate-drive (GD) signal generator622generates the switch control signal CTRL_TPWR based upon a mode, a safety disable signal (SAFETY_DIS), a PWM control signal (PWM_CTRL), and an active-diode control signal (AD_CTRL). If the MODE indicates active-diode mode, the GD signal generator622bases its output on the active-diode control signal (AD_CTRL) provided by the active-diode controller624within the GD signal generator622. If the MODE indicates a PWM (direct-control) mode, the switch control signal CTRL_TPWR is based upon the externally-provided PWM control signal. Additionally, a safety disable (SAFETY_DIS) signal may statically disable the GD signal generator622. The SAFETY_DIS signal may be generated by a controller, such as the controller190, when a fault is detected in the system and the power switch TPWRshould be disabled so as to stop current flow.

The fault detector626may use the voltage VDS_TPWRor current ITPWRof the power switch TPWRto detect faults. For example, a voltage VDS_TPWRor current ITPWRhaving a magnitude above an acceptable value may indicate a problem, in which case the fault detector626issues a fault detect signal FAULT_DET. The fault detect signal may be output from the gate-drive controller620, and may also be provided to the GD signal generator622so as to disable the control signal CTRL_TPWR. The fault detector626preferably operates during both active-diode and PWM modes. In active-diode mode, the active-diode controller624and the fault detector626operate to only turn on the power switch TPWR when the current ILADis within a range between the threshold current ITPWR_THR, and a safety cutoff threshold ITPWR_SAFETY, wherein the currents ILOAD, ITPWR_THR, and ITPWR_SAFETYare negative for the illustrated direction of ILOAD.

FIG. 6Billustrates voltage-current mappings for the power switch TPWRfor the direct-control (PWM) mode. Curve642illustrates the mapping when the switch is turned on, e.g., by the PWM_CTRL signal, whereas curve644illustrates the mapping when the switch is turned off.FIG. 6Cillustrates a voltage-current mapping646for the power switch TPWRfor the active-diode operational mode.

Alternative Gate Drive Controllers

The current ILOADflowing through the power switch TPWRofFIG. 6may be very large for some implementations, which may make sensing this current difficult. For example, if the current ILOADis sensed using a shunt resistor (e.g., at614), the high current may lead to a high power loss in the shunt resistor and the need to use a shunt resistor rated for high power. Additionally, the high current (and associated power) may make the monolithic integration of the gate-drive controller620, the gate driver612, and the power switch TPWRunfeasible. The gate-drive controller720and associated circuitry illustrated inFIG. 7address such issues. Unless described otherwise, the components of the gate-driver controller720may be presumed similar to corresponding components inFIG. 6, though the gate-drive controller720omits some signals and components that are not relevant to the differences in the gate-drive controllers620,720.

The power switch TPWRis augmented with a mirror switch TMIR, which carries a current ITMIRthat is proportional to the current through the power switch TPWR. For example and as is conventional, the mirror switch TMI, may be fabricated in the same technology as the power switch TPWR, but have a different size (width, length) such that the current carried by the mirror switch TMIRis proportionally smaller, e.g., the currents through the switches TPWR, TMIRmay be related with a 1000:1 ratio. A coefficient relating the load current to the sensing current, which is often termed KILIS, may be used to quantify this ratio. The switches TMIR, TPWRare controlled by the same gate driver712. The mirror switch TMIRmay be a part of the power switch TPWRthat is not connected to the load source terminal S, but to a sensing output. The current ITMIRthrough the mirror switch TMIRmay be used to estimate the load current ILOAD. For example, the connection714from the mirror switch TMIRmay include a shunt resistor, and the current sensor7282may use a voltage across the shunt resistor to estimate the current ITMIRand the associated current ILOAD=αITMIR, where α is a positive coefficient related to the relative sizes of the switches TMIR, TPWR. Such an implementation has the advantage that the power loss and power rating of the shunt resistor may be reduced relative to the circuit ofFIG. 6.

In some implementations, the circuitry illustrated inFIG. 7is monolithically integrated on the same semiconductor. The gate-drive controller720comprises primarily digital circuitry that may be implemented with low-cost low-voltage semiconductor processes capable of handling voltage below, e.g., 20V. The mixed-signal circuitry, e.g., the current sensor7282, voltage sensor7284, and gate driver712, may also be implemented using low-voltage circuitry, except that the voltage VDS_TPWRacross the power switch TPWRmay be too large to be sensed by a voltage sensor implemented in a low-voltage semiconductor process. The range of this voltage VDS_TPWRmay be determined by system components, such as the batteries BAT1, BAT2ofFIG. 1.FIG. 8illustrates a low-voltage switch circuit810, which achieves the desired monolithic integration to a high extent while also accommodating high voltage levels that are required by other circuitry with the system.

The power switch TPWRofFIG. 7is partitioned into a high-voltage switch THVand a low-voltage switch TLVin the circuit ofFIG. 8. The high-voltage switch THVis configured to accommodate a high voltage drop across its drain and source terminals, such that the low-voltage switch TLVneed only support a low voltage across its drain and source terminals, as may be supported by a low-voltage semiconductor process. The low-voltage switch TLVmay thus be integrated with the gate-drive controller720, which is able to sense the relatively low voltage VDS_LVof the low-voltage switch TLV. The high-voltage switch THVis implemented outside of the monolithically-integrated low-voltage switch circuit810and may, e.g., be a discrete power switch. The high-voltage switch THVis controlled in the same manner as described previously, but may require a different gate driver813to accommodate its gate voltage requirements.

FIG. 9illustrates another circuit partitioning, in which the power switch TPWRoutputs a current sense signal914. The gate-drive controller920and the gate driver712may be integrated within a low-voltage switch circuit910, as described previously. The current sense signal914is input to a current sensor9282within the gate-drive controller920. As alluded to in the description ofFIG. 6A, the gate-drive controller920uses a sensed current ILOAD_SNSfor triggering the turn on and turn off of the power switch TPWR. For example, the current sensor9282may sense that current is flowing through the body diode and, in response, the turn-on trigger9244sets the active-diode control signal (AD_CTRL) to turn on the power switch TPWR. Once the magnitude of the current ILOAD_SNSreaches a threshold, the turn-off trigger9242resets the active-diode control signal (AD_CTRL) so as to turn off the power switch TPWR.

FIG. 10Aillustrates a bridge circuit1000that may be used as a power stage or as an active rectifier for a 3-phase motor/generator1080. In a first mode, the motor/generator1080is operated as a motor and powered from a battery1070. In a second mode, the motor generator1080is operated as a generator and the battery1070is charged. The gate-drive controllers1020UH,1020UL,1020VH,1020VL,1020WH,1020WL are configured such that the bridge circuit1000may be operated as a power stage for motor mode, or as an active rectifier for generator mode.

The motor/generator1080is comprised of 3 phases, denoted ‘U,’ ‘V,’ and ‘W.’ Each of the phases is connected to a half-bridge circuit. A first half-bridge includes switch circuits1010UH,1010UL, and source/sinks current for phase U. A second half-bridge includes switch circuits1010VH,1010VL, and source/sinks current for phase V. A third half-bridge includes switch circuits1010WH,101WL, and source/sinks current for phase W.

The phase-U high-side switch circuit1010UH is configured similarly to the high-side switch circuit110H ofFIG. 1. More particularly, this circuit1010UH may be operated in an active-diode mode or in a PWM mode. The phase-U low-side switch circuit1010UL is configured similarly to the low-side switch circuit110L ofFIG. 1, and may also be operated in an active-diode or in a PWM mode. Phases V and W have similar associated high and low-side switch circuits1010VH,1010VL,1010WH,1010WL.

When the motor/generator1080is operated in motor mode, the MODE signal provided to each of the GD controllers1020H,1020L is set to PWM mode. PWM control signals PWM_UH, PWM_UL, PWM_VH, PWM_VL, PWM_WH, PWM_WL are generated with appropriate staggering so as to drive the motor in a desired direction and with a desired speed. A controller, not shown for ease of illustration, generates the PWM control signals and the mode signal. Such motor control and PWM signal generation is well-known in the art, and will not be described further.

When the motor/generator1080is operated in generator mode, the MODE signal provided to each of the GD controllers1020H,1020L is set to active-diode mode. PWM signals need not be generated. In active-diode mode, the GD controllers1020H,1020L operate the switches TL, THof each phase as active diodes, wherein current is only allowed to flow in the direction of the body diodes for these switches. Current flows to the battery1070, via terminal1002, so as to charge the battery1070in this mode.

FIG. 10Billustrates waveforms corresponding to winding currents generated during the generator mode operation. For phase U, the high-side switch TI,IHis turned on until time t3, and current flows as illustrated in the direction of IUH_GEN. At time t3, the high-side switch TI,IHis turned off and the low-side switch TULis turned on, resulting in the illustrated current flow IUL_GEN. In like manner, the high-side switches of the other phases are turned on when the illustrated currents IV, IWare positive, and the low-side switches are turned on when these currents are negative. The GD controller configuration allows for the bridge circuit to operate as either a power stage or as an active rectifier. Operation of the bridge circuit as an active rectifier provides better power efficiency than reliance upon the body diode (or other passive diode) rectification, and does not require additional complexity or connections for a controller of the motor/generator1080.

An OBC may comprise an AC/DC converter coupled between the AC grid voltage and an intermediate voltage VDC_GRID, and a DC/DC converter coupled between VDC_GRIDand an output voltage, such as VHV_BAT.FIG. 11illustrates a DC/DC converter1100of an OBC as may be used to charge a high-voltage battery, e.g., in an electric or hybrid vehicle, from an electrical grid. In addition to such charging, the converter1100also supports the flow of energy from the battery back to the grid side of the OBC. Such reverse energy flow enables the use of the high-voltage battery for providing AC power to a house if the electrical grid is down, to AC appliances when the grid is not available but the high-voltage battery is (e.g., when camping), etc. Note that the illustrated converter1100does not show an AC-to-DC (or DC-to-AC) conversion on the grid side, but many systems would include such converters.

The converter1100connects to a primary-side DC supply/sink, having voltage VDC_GRID, using power nodes1102,1102g, and connects to a secondary-side DC supply/sink having voltage VHV_BAT, using power nodes1104,1104g. AC voltage may be handled by an AC-to-DC converter part of the OBC (not shown for ease of illustration). The converter1100further comprises a primary-side power stage1170, a secondary-side power stage1180, an isolation transformer1140, and a controller1190.

The transformer1140includes a primary winding1142, a secondary winding1144, and a core1146. The primary-side power stage1170may be coupled to the primary winding1142via a primary-side inductor LPRIand a primary-side capacitor CPRI, so as to provide an LLC converter topology. Similarly, the secondary-side power stage1180may be coupled to the secondary winding1144via a secondary-side inductor LSECand a secondary-side capacitor CSEC. In other embodiments, the capacitors CPRI, CSECare omitted, as in a full-bridge converter topology that uses zero-voltage switching (ZVS).

The primary-side power stage1170is configured in a full-bridge topology, and may be operated either to supply power to the transformer1140or to actively rectify power supplied by the transformer1140. The power stage1170comprises a first high-side switch circuit110H, a first low-side switch circuit110L, a second high-side switch circuit112H, and a second low-side switch circuit112L. These switch circuits110H,110L,112H,112L are configured as described for the similar circuits110H,110L ofFIG. 1, and may further use the specific embodiments described in conjunction with any ofFIGS. 6 to 9. Notably, each of the switch circuits110H,110L,112H,112L includes gate drive controllers, e.g.,120H,120L. For ease of illustration, the gate drive controllers are not explicitly shown in the switch circuits112H,112L or in the secondary-side power stage1180, but should be understood as being present.

A mode configuration MODE_PRI is provided to the power stage1170and determines whether it should operate in a forward or a reverse mode. In the forward mode, the switch circuits110H,110L,112H,112L are controlled according to switch control signals PWM_A, PWM_B. In a first interval, the signal PWM_A turns on switches THS1, TLS2, via gate-drive controllers120H,122L, so as to apply voltage across the primary-side winding1142. In a second interval, the signal PWM_B turns on switches TLS1, THS2, via gate-drive controllers120L,122H, so as to apply voltage, in an opposite polarity, across the primary-side winding1142. Because such full-bridge operation of an LLC topology is well-known in the art, it will not be described in further detail.

If the mode configuration MODE_PRI indicates operation in the reverse mode, the switches THS1, TLS1, THS2, TLS2of the switch circuits110H,110L,112H,112L are operated as active diodes. This operation is autonomous, i.e., no switch control signals, e.g., PWM_A, PWM_B, need to be generated or supplied to the primary-side power stage1170in this mode. The power stage1170operates, in the reverse mode, as an active rectifier.

The secondary-side power stage1180is configured in largely the same manner as the primary-side power stage1170, and includes power switches THS3, TLS3, THS4, TLS4. Each of these power switches has an associated gate-drive controller and gate driver. For ease of illustration, these components are not explicitly shown, but should be understood to be configured as described above for the like components of the primary-side power stage1170. Switch control signals PWM_C, PWM_D control the power switches THS3, TLS3, THS4, TLS4when the configuration signal MODE_SEC indicates reverse mode, whereas the power switch circuits are operated as active diodes when the configuration signal MODE_SEC indicates forward mode.

The controller1190generates the switch control signals PWM_A, PWM_B, PWM_C, PWM_D and configuration signals MODE_PRI, MODE_SEC. The controller1190may be located on the primary or secondary side of the OBC1100. In typical implementations, at least some of the generated signals will need to pass through isolators to maintain the integrity of the isolation barrier established by the transformer1140. For ease of illustration and because such isolators are well-known, such isolators are not explicitly shown.

While the converter1100ofFIG. 11is described using the specific example of full-bridge power stages arranged in an isolated LLC topology, it should be understood that other embodiments may use other power stage topologies, such as switches arranged in a half bridge. Furthermore, the switches may be controlled using phase-shift control, in which a phase shift between control signals is used to determine the amount of power transfer, rather than PWM control, in which a duty cycle or frequency of the PWM signals is used to determine the amount of power transfer.

Method for Controlling SR Switch

FIG. 12illustrates a method1200for controlling a power switch. This method may be implemented in a gate-drive controller as illustrated, e.g., inFIGS. 1, and 6 to 9. The method begins by determining1210whether a received configuration signal indicates whether the power switch is to be operated in an active-diode or a normal (e.g., PWM) mode. If the normal mode is indicated, the power switch is controlled (turned on and off)1220according to a received PWM control signal. If the active-diode mode is indicated, a drain-to-source voltage VDSof the power switch is sensed and compared against a voltage threshold VDS_ON. If the drain-to-source voltage is sufficiently negative, e.g., below a voltage threshold VDS_ONsuch as −0.1V, the power switch is turned on1240. (Stated alternatively, a source-to-drain voltage above a threshold such as 0.1V triggers the turn on of the power switch.) Similarly and/or alternatively, a positive current through the power switch in the direction of the body diode can trigger the turn on of the power switch. Once the power switch is turned on, forward current ILOAD, which is negative, through the switch is monitored. Once it is detected1250that this (negative) current ILOADrises above a threshold IPWR_THR, the power switch is turned off1260.

Embodiment Variations

According to an embodiment, a method is provided for controlling a power switch having an intrinsic diode configured to conduct current in a reverse direction of the power switch. The method comprises receiving a configuration signal indicating an operational mode for the power switch. If a first mode, which indicates an active-diode configuration, is received, a current and/or voltage of the power switch is sensed and the power switch is turned on if the sensed current and/or voltage indicates positive current, or the potential for positive current, in the reverse direction through the power switch. If a second mode, which indicates a normal (PWM) configuration, is received, the power switch is turned off responsive to receiving a switch control signal directing that the power switch be turned off, and is turned on responsive to receiving a switch control signal directing that the power switch be turned on.

According to any embodiment of the method, the method further includes, responsive to the configuration signal indicating a protected mode, sensing a current and/or voltage of the power switch. The power switch is turned off responsive to at least one of detecting that the sensed current is outside of a normal operating current range, detecting that the sensed voltage is outside of a normal operating voltage range, and receiving a switch control signal directing that the power switch be turned off. The power switch is turned on responsive to receiving a switch control signal directing that the power switch be turned on.

According to any embodiment of the method, sensing the current comprises measuring a voltage across first and second terminals of the power switch and determining the current based upon the voltage. According to an embodiment of this method, responsive to the configuration indicating the first mode (active-diode configuration), turning on the power switch comprises changing a control signal to turn on the power switch in response to detecting that the voltage across the first and second terminals is below a first voltage threshold, which is negative. Subsequently and responsive to detecting that the voltage across the first and second terminals is above a second threshold, the control signal is changed so as to turn off the power switch.

According to an embodiment of a bi-directional switched mode power supply (SMPS), the SMPS comprises first and second SMPS terminals for providing external connections to the SMPS, high and low-side switches, an inductor, a controller, and first and second driver circuits. The high and low-side switches are coupled together at a switching node. The high-side switch is additionally coupled to the first SMPS terminal. Each of the switches comprises an intrinsic diode configured to conduct current in a reverse direction of the switch. The inductor is electrically interposed between the switching node and the second SMPS terminal. The controller is configured to control the power flow between the first and the second SMPS terminals by generating a switch control signal for at least one of the high-side and the low-side switches. The first driver control circuit is configured to control conductivity of the high-side switch based on a sensed current and/or voltage at the high-side switch, responsive to reception of a first switching mode indication (an active-diode mode). The first driver control circuit is configured to control the conductivity of the high-side switch based on the switch control signal generated by the controller, responsive to reception of a second switching mode indication, e.g., a normal or PWM mode. The second driver control circuit is similarly configured to control conductivity of the low-side switch based on a sensed current and/or voltage at the low-side switch, responsive to reception of a first switching mode indication (e.g., an active-diode mode). The second driver control circuit is configured to control conductivity of the low-side switch based on the switch control signal generated by the controller, responsive to reception of the second switching mode indication, e.g., a normal or PWM mode. The SMPS is configured to operate, during a first interval, in a first mode in which power is transferred from the first to the second SMPS terminal, and, during a second interval, in a second mode in which power is transferred from the second to the first SMPS terminal.

According to any embodiment of the SMPS, the first mode is a buck mode, the first SMPS terminal is coupled to a power source, the second SMPS terminal is coupled to a power sink, and a source voltage at the first SMPS terminal is stepped down to provide a sink voltage at the second SMPS terminal, the sink voltage being lower than the source voltage. In a further embodiment of this SMPS, the controller is configured to transmit the first switching mode indication to the second driver control circuit so as to operate the low-side switch in an active-diode configuration, when the SMPS operates in the buck mode.

According to any embodiment of the SMPS, the second mode is a boost mode, the second SMPS terminal is coupled to a power source, the first SMPS terminal is coupled to a power sink, and a source voltage at the second SMPS terminal is stepped up to provide a sink voltage at the first SMPS terminal. The sink voltage is higher than the source voltage. In another embodiment of this SMPS, the controller is configured to transmit the first switching mode indication to the first driver control circuit, so as to set the high-side switch to an active-diode configuration, when the SMPS operates in the boost mode.

According to any embodiment of the SMPS, the SMPS further includes first and second protection switches interposed between the switching node and the second terminal, each of the protection switches comprising intrinsic diodes that are not capable of blocking current in one direction, wherein the protection switches are serially connected such that their intrinsic diodes are oriented in opposite directions. According to a further embodiment of this SMPS, during the first mode, the SMPS operates in a buck mode in which positive current flows to the second SMPS terminal, the first protection switch is set to conduct, and the second protection switch is operated in a first mode (active-diode configuration) in which the second protection switch is turned on responsive to detecting that positive current flows in the direction from the switching node to the second SMPS terminal. According to another embodiment of this SMPS, during the second mode, the SMPS operates in a boost mode in which positive current flows from the second SMPS terminal to the switching node, the second protection switch is set to conduct, and the first protection switch is operated in the first mode (active-diode configuration) in which the first protection switch is turned on responsive to detecting that positive current flows in the direction from the second SMPS terminal to the switching node.

According to an embodiment of a DC/DC converter, the converter comprises first and second direct-current (DC) power nodes, each of which is for connecting to a power source or sink, an isolation transformer comprising primary and secondary windings, a primary-side power stage, a secondary-side power stage and a controller. The primary-side power stage couples the first DC power node to the primary winding. The secondary-side power stage couples the secondary winding to the second DC power node. The secondary-side power stage comprises a secondary-side half bridge including first and second secondary-side power switches arranged in a half-bridge configuration. The secondary-side power stage further comprises first and second secondary-side switch controller circuits coupled, respectively, to the first and second secondary-side power switches. Each of the switch controller circuits is configured for operation in a second (normal) mode, in which an externally-provided switch control signal controls conductivity of the power switch coupled to the switch controller circuit, and a first (active-diode) mode, in which conductivity of the power switch coupled to the switch controller is based upon a sensed current and/or voltage of the power switch. The controller is configured to operate the DC/DC converter, during a first interval, in a forward mode in which power is transferred from the first to the second DC power node, and, during a second interval, in a reverse mode in which power is transferred from the second to the first power node. For the forward mode, the controller sets the secondary-side controller circuits to operate the secondary-side power switches in the active-diode mode. For the reverse mode, the controller sets the secondary-side controller circuits to operate the secondary-side power switches in the normal mode, and generates the externally-provided control signals for the secondary-side power switches.

According to any embodiment of the DC/DC converter, the secondary-side power stage further comprises a second secondary-side half bridge that includes third and fourth secondary-side power switches arranged in a half-bridge configuration, third and fourth secondary-side switch controller circuits configured to operate, respectively, the third and fourth secondary-side power switches in the normal mode or in the active-diode mode, according to a mode setting provided by the controller, and a secondary-side inductor coupled to the secondary winding.

According to any embodiment of the DC/DC converter, the primary-side power stage comprises a primary-side full bridge comprising four primary-side switches, and four primary-side switch controller circuits configured to operate each of the primary-side switches in the normal mode or in the active-diode mode, according to a setting provided by the controller.

According to any embodiment of the DC/DC converter, the converter further comprises a battery coupled to the second DC power node. According to a further embodiment, during the forward mode, the battery is charged from a power source coupled to the first DC power node. According to another embodiment, during the reverse mode, the battery supplies power to a power sink coupled to the first DC power node.