Patent Application
20140103718
1. Field
The disclosed embodiments relate to power supplies for electronic devices. More specifically, the disclosed embodiments relate to techniques for increasing the light-load efficiency of voltage regulators in power supplies using nonlinear inductors with cores of different materials.
2. Related Art
A switched-mode power supply in an electronic device generates an output voltage with a voltage regulator that charges and discharges an inductor using a switched input voltage. The output voltage may then be discharged into a capacitor to drive a load connected to the power supply. Because energy is stored in the inductor and/or capacitor, the switched-mode power supply is generally more efficient than a linear power supply that dissipates excess power in the form of heat.
However, switched-mode power supplies have a number of drawbacks, particularly when used in smaller portable electronic devices such as tablet computers, mobile phones, personal digital assistants (PDAs), and/or portable media players. First, switched-mode power supplies typically include relatively large and expensive inductors compared to other components in the power supplies. The inductors may also be subject to a tradeoff between size and efficiency, in which inductors that are larger and/or more expensive are more efficient than smaller inductors. This tradeoff may interfere with the design of a portable electronic device that needs to be both small and power-efficient.
Inductors in switched-mode power supplies for portable electronic devices may be associated with an additional tradeoff between light-load efficiency and transient response. In particular, a portable electronic device is frequently operated in a low-power state (e.g., a sleep mode) that draws power at very light loads. The efficiency of the switched-mode power supply may be increased at such light loads by increasing the inductance of the inductor in the switched-mode power supply. On the other hand, the response of the switched-mode power supply to transient loads (e.g., during use of the portable electronic device) may be improved by reducing the inductance of the inductor and/or increasing the speed of the control loop for the switched-mode power supply, which decreases the efficiency of the switched-mode power supply.
Hence, the use of portable electronic devices may be facilitated by managing the tradeoffs among size, efficiency, and transient response of power supplies for the portable electronic devices.
The disclosed embodiments relate to a power supply for a portable electronic device. The power supply includes a power source and a nonlinear inductor. The nonlinear inductor includes a first core and a second core connected in series to the first core, wherein the second core has a higher permeability than the first core.
In some embodiments, the second core lacks an air gap.
In some embodiments, the second core is smaller than the first core.
In some embodiments, the first and second cores are used in a power supply for a portable electronic device.
In some embodiments, the power supply is operated using at least one of a continuous conduction mode (CCM) and a discontinuous conduction mode (DCM).
In some embodiments, a material of the first core is at least one of:
powdered iron and sand dust.
In some embodiments, a material of the second core is at least one of ferrite, nickel zinc, and nickel manganese.
In the figures, like reference numerals refer to the same figure elements.
The following description is presented to enable any person skilled in the art to make and use the embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
The data structures and code described in this detailed description are typically stored on a computer-readable storage medium, which may be any device or medium that can store code and/or data for use by a computer system. The computer-readable storage medium includes, but is not limited to, volatile memory, non-volatile memory, magnetic and optical storage devices such as disk drives, magnetic tape, CDs (compact discs), DVDs (digital versatile discs or digital video discs), or other media capable of storing code and/or data now known or later developed.
The methods and processes described in the detailed description section can be embodied as code and/or data, which can be stored in a computer-readable storage medium as described above. When a computer system reads and executes the code and/or data stored on the computer-readable storage medium, the computer system performs the methods and processes embodied as data structures and code and stored within the computer-readable storage medium.
Furthermore, methods and processes described herein can be included in hardware modules or apparatus. These modules or apparatus may include, but are not limited to, an application-specific integrated circuit (ASIC) chip, a field-programmable gate array (FPGA), a dedicated or shared processor that executes a particular software module or a piece of code at a particular time, and/or other programmable-logic devices now known or later developed. When the hardware modules or apparatus are activated, they perform the methods and processes included within them.
The disclosed embodiments relate to a power supply for an electronic device. As shown in
In one or more embodiments, power supply 100 supplies power to components (e.g., components 122-128) in a portable electronic device such as a laptop computer, tablet computer, mobile phone, personal digital assistant (PDA), portable media player, and/or digital camera. Consequently, power source 110 may include a battery or battery pack in the portable electronic device, such as a lithium-ion and/or lithium-polymer battery pack.
Furthermore, power supply 100 may be designed to accommodate size and/or power constraints associated with the portable electronic device. In particular, the powering of the portable electronic device from a battery may require a level of power efficiency in the portable electronic device, while the form factor of the portable electronic device may restrict the use of larger and/or heavier components in the portable electronic device. As a result, power supply 100 may be a switched-mode power supply that converts voltage from power source 110 using inductors and/or capacitors, instead of a larger, heavier, and/or more inefficient linear regulated power supply that dissipates excess voltage as heat.
However, switched-mode power supplies may be associated with tradeoffs among size, efficiency, and/or transient response. For example, a larger inductor may generate a given output voltage at a lower switching frequency, and thus dissipate less power, than a smaller inductor that takes up less space in the portable electronic device. On the other hand, the smaller inductor may enable faster switching that results in both a faster transient response and increased power dissipation than a larger, more efficient inductor.
In one or more embodiments, voltage regulator 120 includes a nonlinear inductor with a high inductance at low currents and a low inductance at high currents. As discussed in further detail below with respect to
First, control circuit 202 may periodically charge and discharge nonlinear inductor 212 by coupling the input terminal of nonlinear inductor 212 to either power source 220 or a reference voltage (e.g., ground). Control circuit 202 may cause nonlinear inductor 212 to enter a charge phase by closing a control FET 204 and opening a synchronous FET 206. During the charge phase, the input terminal of nonlinear inductor 212 is coupled to power source 220, and a positive voltage drop develops across nonlinear inductor 212 as inductor current increases.
Conversely, control circuit 202 may cause nonlinear inductor 212 to enter a discharge phase by opening control FET 204 and closing synchronous FET 206. During the discharge phase, the input terminal of nonlinear inductor 212 is coupled to the reference voltage, a negative voltage drop develops across nonlinear inductor 212 as current stored in nonlinear inductor 212 discharges, and a return path for the discharging nonlinear inductor 212 is provided by synchronous FET 206. Consequently, FETs 204-206 may provide an input switch that switches the input voltage supplied to the input terminal of nonlinear inductor 212 at a switch node 222 of the circuit. Capacitor 214 may then collect current discharging from nonlinear inductor 212, supply the current to load 218, and act as a low-pass filter by reducing voltage ripple caused by fluctuating current through nonlinear inductor 212.
In addition, control circuit 202 may vary the switching frequency of the input switch based on load 218. For example, control circuit 202 may operate in a continuous conduction mode (CCM) that maintains a continuous current in nonlinear inductor 212 whenever load 218 current is above a threshold (e.g., a critical current of nonlinear inductor 212). The CCM may thus be used to supply power to a transient load 218, such as during use of a portable electronic device corresponding to load 218. Alternatively, control circuit 202 may operate in a discontinuous conduction mode (DCM) that includes periods of zero inductor current in between charging and discharging of nonlinear inductor 212 whenever load 218 current is below the threshold. As a result, the DCM may be used to supply power to a light load 218, such as during a sleep mode of the portable electronic device.
To improve the transient response of the voltage regulator during CCM while maintaining efficiency during DCM, nonlinear inductor 212 may include two cores 208-210 connected in series. Cores 208-210 may include a first, larger core with a relatively low permeability and a second, smaller core with a relatively high permeability. For example, the first core may include powdered iron and/or sand dust core, while the second core may include ferrite, nickel zinc, and/or nickel manganese.
Consequently, the second core may have a higher inductance and/or saturate more quickly than the first core. For example, the first core may have an inductance of 0.2 mH, while the second core may have an inductance of 0.6 mH. In turn, the coupling of cores 208-210 in series may allow the characteristics of cores 208-210 to be combined in nonlinear inductor 212, as discussed in further detail below with respect to
Because lower inductance is provided by the first core, the second core may lack an air gap that normally decreases the inductance of the second core and/or the flux around the windings of the second core. The lack of an air gap may further result in less magnetic leakage and/or fewer mechanical issues for the second core than in conventional high-permeability inductor cores that contain air gaps.
The high value of inductance 302 for low load current 304 and/or light load 306 may be provided by the second core in the linear inductor, which has a higher permeability than the first core but saturates quickly at high load current 304. For example, inductance 302 may be the sum of the inductances of the first and second cores while load current 304 is within the range corresponding to light load 306. The second core may then saturate after load current 304 enters into the range corresponding to transient load 308, thus reducing inductance 302 significantly.
Inductance 302 may thus enable both light-load efficiency and fast transient response for a voltage regulator containing the nonlinear inductor. For example, the large inductance 302 at light load 306 may allow the voltage regulator to operate at a lower switching frequency (e.g., during DCM), which reduces switching losses in the voltage regulator. On the other hand, the low inductance 302 at transient load 308 may increase the switching frequency of the voltage regulator (e.g., during CCM) and allow the voltage regulator to react quickly to changes in transient load 308.
First, a nonlinear inductor containing a first core and a second core connected in series to the first core is provided (operation 402). The second core may be smaller than the first core and have a higher permeability than the first core. For example, the second core may be smaller than the first core and include ferrite, nickel zinc, and/or nickel manganese, while the first core may include powdered iron and/or sand dust. The second core may also lack an air gap normally associated with high-permeability inductor cores.
Next, the inductor is used to transfer power from a power source to the components (operation 404). For example, the inductor may be used in CCM and/or DCM of a voltage regulator that converts input voltage from the power source into an output voltage and/or current that can be used by the components. The first and second cores may provide a relatively high inductance at low load currents that enables efficient operation of the voltage regulator at light loads (e.g., during a sleep mode of the portable electronic device). The saturation of the second core at high load currents may then lower the inductance of the nonlinear inductor, thus allowing the voltage regulator to respond quickly to transient loads (e.g., during use of the portable electronic device).
The above-described nonlinear inductor can generally be used in any type of electronic device. For example,
The foregoing descriptions of various embodiments have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention.
