Battery charger power control

Certain aspects of the present disclosure relate to methods and apparatus for limiting the power drawn by a battery charger based on monitoring of the input voltage and input current supplied to the battery charger from a power supply. In certain aspects, a method generally includes sensing an output voltage of the power supply, wherein the output voltage of the power supply is variable. The method further includes sensing an output current of the power supply. The method further includes providing the output voltage and output current to a battery charger. The method further includes generating a control signal indicative of a scaling of the output current based on a scaling factor, wherein the scaling factor is based on the output voltage. The method further includes providing the control signal to the battery charger to control the output current supplied by the power supply to the battery charger.

TECHNICAL FIELD

The present disclosure relates generally to power supply control, and in particular to limiting the power drawn by a battery charger based on monitoring of the input voltage and input current supplied to the battery charger from a power supply.

BACKGROUND

An increasing number and variety of electronic devices are powered via rechargeable batteries. Such devices include mobile phones, portable music players, laptop computers, tablet computers, computer peripheral devices, communication devices (e.g., Bluetooth devices), digital cameras, hearing aids, medical implants, and the like. While battery technology has improved, battery-powered electronic devices increasingly require and consume greater amounts of power. As such, these devices constantly require recharging.

Rechargeable devices may be charged via wired connections that require cables or other similar connectors that are physically connected to a power supply. In other cases, rechargeable devices may be charged wirelessly. Wireless power transfer systems, for example, may allow users to charge and/or power electronic devices without physical, electrical connections.

The batteries in the rechargeable device may be configured to be charged at particular power levels or voltages. Accordingly, systems and methods for controlling the power supplied to a battery may be desirable.

SUMMARY

Certain aspects provide a method for supplying power to a battery charger. The method generally includes sensing an output voltage of a power supply, wherein the output voltage of the power supply is variable. The method further includes sensing an output current of the power supply. The method further includes providing the output voltage and output current to the battery charger. The method further includes generating a control signal indicative of a scaling of the output current based on a scaling factor, wherein the scaling factor is based on the output voltage. The method further includes providing the control signal to the battery charger to control the output current drawn from the power supply by the battery charger.

Certain aspects provide a power supply for supplying power to a battery charger. The power supply generally includes an output terminal configured to provide an output voltage and output current to the battery charger. The power supply further includes a sensing circuit configured to sense the output voltage and the output current. The power supply further includes a control circuit configured to generate a control signal indicative of a scaling of the output current based on a scaling factor, wherein the scaling factor is based on the output voltage, and provide the control signal to the battery charger to control the output current to the battery charger.

Certain aspects provide a power supply for supplying power to a battery charger. The power supply generally includes means for sensing an output voltage of the power supply, wherein the output voltage of the power supply is variable. The power supply further includes means for sensing an output current of the power supply. The power supply further includes means for providing the output voltage and output current to the battery charger. The power supply further includes means for generating a control signal indicative of a scaling of the output current based on a scaling factor, wherein the scaling factor is based on the output voltage. The power supply further includes means for providing the control signal to the battery charger to control the output current drawn from the power supply by the battery charger.

Certain aspects provide a computer readable medium having instructions stored thereon for causing a power supply to perform a method for supplying power to a battery charger. The method generally includes sensing an output voltage of the power supply, wherein the output voltage of the power supply is variable. The method further includes sensing an output current of the power supply. The method further includes providing the output voltage and output current to the battery charger. The method further includes generating a control signal indicative of a scaling of the output current based on a scaling factor, wherein the scaling factor is based on the output voltage. The method further includes providing the control signal to the battery charger to control the output current drawn from the power supply by the battery charger.

DETAILED DESCRIPTION

Drawing elements that are common among the following figures may be identified using the same reference numerals.

To charge a battery, a power supply may be coupled to a battery charger and the battery charger may be coupled to the battery. Accordingly, the battery charger can regulate the amount of power from the power supply that is applied to the battery for charging the battery.

In certain cases, a power supply may have a maximum power it can supply, and a battery charger may have a maximum power it can receive as input. Further, the voltage output from the power supply may vary (e.g., due to different charging profiles, fluctuations in a supply voltage to the power supply, variations in induced voltage in a wireless power supply, etc.). Accordingly, some aspects herein relate to limiting the power drawn by a battery charger from a power supply based on monitoring of the input voltage and input current supplied to the battery charger from the power supply. Such limiting of the power drawn by the battery charger can help prevent the power supply and battery charger from exceeding their respective maximum power limits.

In some aspects, the power supply is a wired power supply. For example, the power supply may include an AC/DC power adapter that plugs into a main power supply and provides a DC output. The wired power supply may have a wired connection (e.g., via a USB interface) to a charging port of a rechargeable device that is coupled to the battery charger inside the rechargeable device.

In some aspects, the power supply is a wireless power supply, such as described below with respect toFIGS. 1-3.

Wireless power transfer may refer to transferring any form of energy associated with electric fields, magnetic fields, electromagnetic fields, or otherwise from a transmitter to a receiver without the use of physical electrical conductors (e.g., power may be transferred through free space). The power output into a wireless field (e.g., a magnetic field or an electromagnetic field) may be received, captured by, or coupled by a “power receiving element” to achieve power transfer.

FIG. 1is a functional block diagram of a wireless power transfer system100, in accordance with an illustrative aspect. Input power102may be provided to a transmitter104from a power source (not shown in this figure) to generate a wireless (e.g., magnetic or electromagnetic) field105for performing energy transfer. A receiver108may couple to the wireless field105and generate output power110for storing or consumption by a device (not shown in this figure) coupled to the output power110. The transmitter104and the receiver108may be separated by a distance112. The transmitter104may include a power transmitting element114for transmitting/coupling energy to the receiver108. The receiver108may include a power receiving element118for receiving or capturing/coupling energy transmitted from the transmitter104.

In one illustrative aspect, the transmitter104and the receiver108may be configured according to a mutual resonant relationship. When the resonant frequency of the receiver108and the resonant frequency of the transmitter104are substantially the same or very close, transmission losses between the transmitter104and the receiver108are reduced. As such, wireless power transfer may be provided over larger distances. Resonant inductive coupling techniques may thus allow for improved efficiency and power transfer over various distances and with a variety of inductive power transmitting and receiving element configurations.

In certain aspects, the wireless field105may correspond to the “near field” of the transmitter104. The near-field may correspond to a region in which there are strong reactive fields resulting from the currents and charges in the power transmitting element114that minimally radiate power away from the power transmitting element114. The near-field may correspond to a region that is within about one wavelength (or a fraction thereof) of the power transmitting element114. Conversely, the far field may correspond to a region that is greater than about one wavelength of the power transmitting element114.

In certain aspects, efficient energy transfer may occur by coupling a large portion of the energy in the wireless field105to the power receiving element118rather than propagating most of the energy in an electromagnetic wave to the far field.

In certain implementations, the transmitter104may output a time varying magnetic (or electromagnetic) field with a frequency corresponding to the resonant frequency of the power transmitting element114. When the receiver108is within the wireless field105, the time varying magnetic (or electromagnetic) field may induce a current in the power receiving element118. As described above, if the power receiving element118is configured as a resonant circuit to resonate at the frequency of the power transmitting element114, energy may be efficiently transferred. An alternating current (AC) signal induced in the power receiving element118may be rectified to produce a direct current (DC) signal that may be provided to charge or to power a load.

FIG. 2is a functional block diagram of a wireless power transfer system200, in accordance with another illustrative aspect. The system200may include a transmitter204and a receiver208. The transmitter204(also referred to herein as power transfer unit, PTU) may include transmit circuitry206that may include an oscillator222, a driver circuit224, and a front-end circuit226. The oscillator222may be configured to generate an oscillator signal (e.g., an oscillating signal) at a desired frequency (e.g., fundamental frequency) that may adjust in response to a frequency control signal223. The oscillator222may provide the oscillator signal to the driver circuit224. The driver circuit224may be configured to drive the power transmitting element214at, for example, a resonant frequency of the power transmitting element214based on an input voltage signal (VD)225. The driver circuit224may be a switching amplifier configured to receive a square wave from the oscillator222and output as a driving signal output a sine wave.

The front-end circuit226may include a filter circuit configured to filter out harmonics or other unwanted frequencies. The front-end circuit226may include a matching circuit configured to match the impedance of the transmitter204to the impedance of the power transmitting element214. As will be explained in more detail below, the front-end circuit226may include a tuning circuit to create a resonant circuit with the power transmitting element214. As a result of driving the power transmitting element214, the power transmitting element214may generate a wireless field205to wirelessly output power at a level sufficient for charging a battery236, or otherwise powering a load.

The transmitter204may further include a controller240operably coupled to the transmit circuitry206and configured to control one or more aspects of the transmit circuitry206, or accomplish other operations relevant to managing the transfer of power. The controller240may be a micro-controller or a processor. The controller240may be implemented as an application-specific integrated circuit (ASIC). The controller240may be operably connected, directly or indirectly, to each component of the transmit circuitry206. The controller240may be further configured to receive information from each of the components of the transmit circuitry206and perform calculations based on the received information. The controller240may be configured to generate control signals (e.g., signal223) for each of the components that may adjust the operation of that component. As such, the controller240may be configured to adjust or manage the power transfer based on a result of the operations performed by it. The transmitter204may further include a memory (not shown) configured to store data, for example, such as instructions for causing the controller240to perform particular functions, such as those related to management of wireless power transfer.

The receiver208(also referred to herein as power receiving unit, PRU) may include receive circuitry210that may include a front-end circuit232and a rectifier circuit234. The front-end circuit232may include matching circuitry configured to match the impedance of the receive circuitry210to the impedance of the power receiving element218. As will be explained below, the front-end circuit232may further include a tuning circuit to create a resonant circuit with the power receiving element218. The rectifier circuit234may generate a DC power output from an AC power input to charge the battery236, as shown inFIG. 2. The receiver208and the transmitter204may additionally communicate on a separate communication channel219(e.g., Bluetooth, Zigbee, cellular, etc.). The receiver208and the transmitter204may alternatively communicate via in-band signaling using characteristics of the wireless field205.

The receiver208may be configured to determine whether an amount of power transmitted by the transmitter204and received by the receiver208is appropriate for charging the battery236. In certain aspects, the transmitter204may be configured to generate a predominantly non-radiative field with a direct field coupling coefficient (k) for providing energy transfer. Receiver208may directly couple to the wireless field205and may generate an output power for storing or consumption by a battery (or load)236coupled to the output or receive circuitry210.

The receiver208may further include a controller250configured similarly to the transmit controller240as described above for managing one or more aspects of the wireless power receiver208. The receiver208may further include a memory (not shown) configured to store data, for example, such as instructions for causing the controller250to perform particular functions, such as those related to management of wireless power transfer.

As discussed above, transmitter204and receiver208may be separated by a distance and may be configured according to a mutual resonant relationship to minimize transmission losses between the transmitter204and the receiver208.

FIG. 3is a schematic diagram of a portion of the transmit circuitry206or the receive circuitry210ofFIG. 2, in accordance with illustrative aspects. As illustrated inFIG. 3, transmit or receive circuitry350may include a power transmitting or receiving element352and a tuning circuit360. The power transmitting or receiving element352may also be referred to or be configured as an antenna or a “loop” antenna. The term “antenna” generally refers to a component that may wirelessly output or receive energy for coupling to another antenna. The power transmitting or receiving element352may also be referred to herein or be configured as a “magnetic” antenna, or an induction coil, a resonator, or a portion of a resonator. The power transmitting or receiving element352may also be referred to as a coil or resonator of a type that is configured to wirelessly output or receive power. As used herein, the power transmitting or receiving element352is an example of a “power transfer component” of a type that is configured to wirelessly output and/or receive power. The power transmitting or receiving element352may include an air core or a physical core such as a ferrite core (not shown in this figure).

When the power transmitting or receiving element352is configured as a resonant circuit or resonator with tuning circuit360, the resonant frequency of the power transmitting or receiving element352may be based on the inductance and capacitance. Inductance may be simply the inductance created by a coil and/or other inductor forming the power transmitting or receiving element352. Capacitance (e.g., a capacitor) may be provided by the tuning circuit360to create a resonant structure at a desired resonant frequency. As a non limiting example, the tuning circuit360may comprise a capacitor354and a capacitor356, which may be added to the transmit and/or receive circuitry350to create a resonant circuit.

The tuning circuit360may include other components to form a resonant circuit with the power transmitting or receiving element352. As another non limiting example, the tuning circuit360may include a capacitor (not shown) placed in parallel between the two terminals of the circuitry350. Still other designs are possible. In some aspects, the tuning circuit in the front-end circuit226may have the same design (e.g.,360) as the tuning circuit in front-end circuit232. In other aspects, the front-end circuit226may use a tuning circuit design different than in the front-end circuit232.

For power transmitting elements, the signal358, with a frequency that substantially corresponds to the resonant frequency of the power transmitting or receiving element352, may be an input to the power transmitting or receiving element352. For power receiving elements, the signal358, with a frequency that substantially corresponds to the resonant frequency of the power transmitting or receiving element352, may be an output from the power transmitting or receiving element352.

Although aspects disclosed herein may be used in systems related to resonant wireless power transfer, persons of ordinary skill will appreciate that aspects disclosed herein may be used in other non-resonant implementations for wireless power transfer, and in wired power applications, such as those described above. In particular, some aspects herein relate to limiting the power drawn by a battery charger based on monitoring of the input voltage and input current supplied to the battery charger from a power supply. For example, certain aspects herein relate to controlling power drawn by a battery charger used to charge a battery based on an input voltage from a power supply (e.g., a wireless power receiver).

In certain aspects, the induced voltage at a wireless power receiver (e.g., receiver208) due to a wireless field (e.g., wireless field205generated by a wireless power transmitter (e.g., transmitter204) may vary. For example, the coupling between the wireless power receiver208and the wireless power transmitter204may change due to distance or material between the receiver208and the transmitter204, leading to variations in induced voltage at the receiver208.

Certain devices (e.g., charge ports of mobile devices, battery operated devices, etc.) may be configured to only accept a limited range of voltages (e.g., 4-10V, 4-12V, etc.). Since the induced voltage at the receiver208may vary due to the variable mutual inductance between the transmitter204and the receiver208, circuits may be used to scale the voltage of the receiver208. Further, a power supply may have a maximum power it can supply, and a battery charger may have a maximum power it can receive as input. Since the voltage at the receiver208may vary, the current output by the power supply and input to the battery charger may need to be controlled to ensure the power limits are not exceeded.

FIG. 4illustrates a battery charging system400including a buck converter, in accordance with certain aspects. As shown, the charging system400includes a power supply405(e.g., receiver208) and a battery charger455. The acceptable input voltage range of the battery charger455may be limited (e.g., 4-10V, 4-12V, etc.).

The power supply405generates a power signal shown as having a voltage VRECT. For example, where the power supply405comprises a wireless power receiver such as receiver208, the power signal with voltage VRECTmay be generated by the rectifier234, as described herein. The power supply405further includes a sensing circuit410configured to sense the voltage level and current of the power signal generated. The power supply405further includes a buck converter415that receives the power signal and limits a voltage and current of the power signal as output by the buck converter415. The buck converter415includes a control circuit417, a gate driver419, and transistors421coupled in series. The control circuit417receives information from the sensing circuit410as to the voltage VRECTof the power signal and current of the power signal and controls the gate driver419to selectively open and close transistors421to limit the voltage output and current output by the buck converter415, and accordingly the voltage output and current output by the power supply405. In particular, the buck converter415limits the output voltage to a voltage within an acceptable range and a current output to a current within an acceptable range (e.g., based on a power limit for the battery charger455and for the power supply405). The output of the buck converter415is further coupled to an inductor425, which is coupled to an input of the battery charger455. The inductor425may ensure the input voltage at the battery charger455is within the acceptable range. The battery charger455itself further includes a buck converter460shown as a series of transistors462. The buck converter460may further control the voltage and current applied to a battery (e.g., battery236) to charge the battery. The output of the buck converter460is further coupled to an inductor465, which is coupled to an input of the battery. The inductor465ensures the input voltage at the battery is within the desired voltage range. Accordingly, the battery charging system400includes cascaded buck converters415and460, in order to control the voltage and current output by the battery charger455to a battery (e.g., battery236). These cascaded buck converters415and460, along with two inductors415and465may be costly (e.g., require large silicon area to implement) and further may suffer from significant losses (e.g., power losses, power efficiency of 90% or less) and heat dissipation due to the current control performed by both the buck converter415and the buck converter460.

FIG. 5illustrates a battery charging system500including an open loop charge pump, in accordance with certain aspects. As shown, the charging system500includes a power supply505(e.g., receiver208) and a battery charger555. The acceptable input voltage range of the battery charger555may be limited (e.g., 4-10V, 4-12V, etc.).

The power supply505generates a power signal shown as having a voltage VRECT. For example, where the power supply505comprises a wireless power receiver such as receiver208, the power signal with voltage VRECTmay be generated by the rectifier234, as described herein. The power supply505further includes a sensing circuit510configured to sense the voltage level and current of the power signal generated. The power supply505further includes an open loop charge pump515(e.g., divide by two charge pump) that receives the power signal and limits a voltage and current of the power signal as output by the charge pump515.

In certain aspects, the charge pump515may operate in a divide-by-two mode, where the output voltage Vout of the charge pump515is half of the input voltage Vin of the charge pump515(Vout=Vin/2). In certain aspects, the charge pump515may operate in a bypass mode where the output voltage Vout of the charge pump400is equal to the input voltage Vin.

As shown, the charge pump515includes transistors517. In some aspects, gate terminals of each of the transistors517may be coupled to control signals (e.g., from a controller, such as, a PMIC, processor, controller250, etc.) to control the opening and closing of transistors517. The controller receives information from the sensing circuit510as to the voltage VRECTof the power signal and current of the power signal and controls the transistors517to limit the voltage output and current output by the charge pump515, and accordingly the voltage output and current output by the power supply505to the battery charger555. In particular, the charge pump515limits the output voltage to a voltage within an acceptable range and a current output to a current within an acceptable range (e.g., based on a power limit for the battery charger555). However, in order to limit the output voltage and output current, the charge pump515may need to receive feedback (e.g., input power limit) from the battery charger555, and the battery charger may need to support input power limit. Therefore, design of the charge pump515may need to be tightly coupled with design of the battery charger555, which adds complexity and cost to design of the charging system500.

Accordingly, to overcome some of the limitations of charging system400and500, and other similar charging systems, certain aspects described herein provide for controlling an output current of a battery charger used to charge a battery based on an input voltage from a power supply (e.g., a wireless power receiver).

FIG. 6illustrates a battery charging system600including a feed forward control system, in accordance with certain aspects. As shown, the charging system600includes a power supply605(e.g., receiver208) and a battery charger655. The acceptable input voltage range of the battery charger655may be limited (e.g., 4-10V, 4-12V, etc.).

The power supply605generates a power signal shown as having a voltage VRECT. For example, where the power supply605comprises a wireless power receiver such as receiver208, the power signal with voltage VRECTmay be generated by the rectifier234, as described herein. The power supply605further includes a sensing and control circuit610configured to sense the current and voltage of the power signal generated. In some aspects, the power supply605further includes a voltage limiter615(e.g., charge pump, buck converter, variable capacitor, impedance transformer, etc.) that is configured to limit the voltage output of the power supply605. In some aspects, the power supply may not, however, limit a current output of the power supply605. Further, the voltage limiter615may be configured to limit the output voltage of the power supply605to a range, but not necessarily a fixed voltage. In some aspects, the voltage limiter615is configured to operate in a bypass mode if VRECTis below a maximum operating voltage of the battery charger655, and operate in a step down mode (e.g., divide by 2 mode) to limit the voltage when VRECTis above a maximum operating voltage of the battery charger655.

In some aspects, if the power supply605already has an acceptable voltage output limit (e.g., based on a design of receiver208, VRECTis already limited to the acceptable input voltage range of battery charger655) the power supply605may not include the voltage limiter615.

The battery charger655, similar to battery charger455, includes a buck converter660(or other appropriate regulator). The buck converter660includes an interface657(e.g., a pulse-width modulation (PWM) comparator), a gate driver659, and transistors661coupled in series. The interface657provides the gate driver659a signal to selectively open and close transistors661to limit the power output (e.g., voltage and current output) by the buck converter660(e.g., by performing power and impedance limiting), and accordingly the power output by the battery charger655. In particular, in certain aspects, the signal provided by the interface657is controlled by a feed forward control signal from sensing and control circuit610. In certain aspects, the logic for controlling the selective opening and closing of transistors661(e.g., for generating the feed forward control signal) to limit the power output by the buck converter660is implemented in the sensing and control circuit610as further discussed herein. For example, the interface657may be configured to receive a signal from the sensing and control circuit610and convert the signal to one that drives the gate driver659. For example, the gate driver659may be configured to operate based on a pulse-width modulated signal. Accordingly, the interface657may be configured to generate a pulse-width modulated waveform with a duty cycle that is proportional (e.g., inversely proportional) to the signal received from the sensing and control circuit610and apply the waveform to the gate driver659.

The sensing and control circuit610may be configured to generate (e.g., in whole or in part) a feed forward control signal and send the signal on line617to the battery charger655to control the power usage of the battery charger655based on an output voltage of the power supply605. In particular, as discussed, the power supply605may have a maximum power output (POUT_MAX) that it can supply, and the battery charger655may have a maximum power input (PIN_MAX) it can handle. Accordingly, the power usage of the battery charger655may be controlled to ensure that the power limits are met. In particular, in some aspects, the feed forward control signal is configured to control the battery charger655to limit the current drawn by the battery charger655to ensure the power limits are met. Further, as discussed above, in some aspects, the output voltage of the power supply605is not fixed, and therefore may vary. Accordingly, in certain aspects, the feed forward control signal is based on the output voltage to ensure the current used by the battery charger655for the actual output voltage meets the power limits.

Accordingly the battery charging system600can operate in an open loop design (e.g., based on the current loop control) to operate more efficiently than battery charging system400, and without added complexity like battery charging system500. Further, since the battery charging system600can operate with a variable output voltage for the power supply605, in some aspects, the output voltage may be selected to operate in an optimal range for the battery charger655, thereby further increasing efficiency. In addition, in some aspects, the battery charger655and power supply605do not need to be specifically designed for each other (e.g., to have specific voltage inputs and output) as the feed forward control signal ensures proper operation even with variable voltages.

In certain aspects, a control loop error amplifier670, as shown inFIG. 6A, is used to generate a signal as input to interface657to set the current drawn by battery charger655. In particular, a first input of the control loop error amplifier670is coupled to a line carrying a signal with a voltage level indicative of the current sensed by sensing and control circuit610. Further, a second input of the control loop error amplifier670is coupled to a line carrying a reference signal with a reference voltage VREF. VREF may be selected (e.g., programmed, set, etc.) such that the control loop error amplifier670ensures that the current drawn by the battery charger655does not exceed the power limit of either the battery charger655or the power supply605.

For example, in certain aspects, VREF is configured based on maximum power input PIN_MAX and a minimum input voltage (DCIN_MIN) for the battery charger655to represent the maximum input current for the battery charger655. For example, if PIN_MAX is 10 W and DCIN_MIN is 5V, VREF is configured to represent the maximum input current of2A for the battery charger655. Depending on the design of battery charger655, M volts of VREF may correspond to N amps drawn by the battery charger655(e.g., 100 mV corresponds to 100 mA), and therefore VREF is set to (M/N)*(PIN MAX/DCIN_MIN) (e.g., 2V). In particular, in certain aspects, the correspondence of M and N may be based on the assumption that the input voltage to the battery charger655is DCIN_MIN. Accordingly, in certain aspects the selection of VREF for the control loop error amplifier670is independent of the power supply605(e.g., the power limit and voltage supplied by the power supply605).

Based on the selection of VREF as discussed, if the actual voltage supplied by the power supply605to the battery charger655is DCIN_MIN, and the power supply has a POUT_MAX equal to PIN_MAX, then the described correspondence of voltage M to current N holds true. Accordingly, the control loop error amplifier670can use the actual sensed current from sensing and control circuit610to properly limit current drawn by the battery charger655to not exceed the power limit of the battery charger655or the power supply605. However, if the actual voltage supplied by the power supply605is not DCIN_MIN and/or POUT_MAX is not equal to PIN MAX, then using the actual sensed current may lead to the control loop error amplifier670improperly limiting current drawn by the battery charger655.

Accordingly, in certain aspects, the signal on the line coupled to the first input of the control loop error amplifier670is indicative of a scaled current sensed by sensing and control circuit610. In particular, the current sensed by sensing and control circuit610is scaled by a scaling factor equal to the maximum input current to the battery charger655divided by the maximum output current of the power supply605, which is:
(PIN_MAX/DCIN_MAX)/(POUT_MAX/VOUT),

where VOUT is the actual voltage supplied by the power supply605. The scaling may be performed, for example, by a scaled current mirror coupled to a current sensing circuit, each of which are implemented in the sensing and control circuit610. Accordingly, the current sensed by the sensing and control circuit610is scaled based on the output voltage of the power supply605, and the scaled current is used by the control loop error amplifier670to control the current of the battery charger655. Accordingly, the current drawn by the battery charger655is controlled based on the current sensed at power supply605, which is scaled based on the output voltage of the power supply605. By using the scaled current instead of the actual current sensed at power supply605, the current drawn by the battery charger655can be properly controlled even if the actual voltage supplied by the power supply605is not DCIN_MIN and/or POUT_MAX is not equal to PIN_MAX.

In certain aspects, the control loop error amplifier670is implemented in the battery charger655, such as shown inFIG. 6B. In such aspects, the feed forward control signal generated by control circuit610may be indicative of the scaled current generated by the sensing and control circuit610. For example, in the example shown inFIG. 6B, the feed forward control signal is the scaled current (e.g., a current based control signal), which is converted to an appropriate voltage signal at battery charger655with a resistor675coupled to the line carrying the signal to the control loop error amplifier670. In some aspects, the resistor675may be implemented at the power supply605instead of the battery charger655, and the feed forward control signal sent from the power supply605to the battery charger655may be the appropriate voltage signal (e.g., a voltage based control signal).

In certain aspects, the control loop error amplifier670is implemented in the power supply605, such as shown inFIG. 6C. In such aspects, the feed forward control signal from the power supply605to the battery charger655may be the output signal of the control loop error amplifier670and directly coupled to interface657. Such an output signal may still be based on the scaled current as discussed. Though resistor675is not shown inFIG. 6C, it may be implemented in sensing and control circuit610.

In certain aspects, the sensing and control circuit610may fully implement a current control loop as discussed herein and generate a pulse width modulation (PWM) signal to directly control the transistors661.

FIG. 7is a flowchart of example operations700for operating a battery charging system including a feed forward control system, in accordance with certain aspects of the present disclosure.

At705, a power supply senses an output voltage of the power supply to a battery charger. Further, at710, the power supply senses an output current of the power supply to the battery charger.

At715, the power supply provides the output voltage and the output current to the battery charger. At720, the power supply generates a control signal for controlling the output current by the battery charger. In some aspects, as discussed, the control signal is indicative of a scaling of the output current based on a scaling factor. The scaling factor is based on the output voltage. At725, the power supply provides the control signal to the battery charger to control the output current. For example, the battery charger, in some aspects, utilizes the scaled current to control the current drawn by the battery charger, such as to comply with power limits of the power supply and the battery charger.