U.S. patent application number 11/980182 was filed with the patent office on 2009-04-30 for bidirectional power converters.
This patent application is currently assigned to Linear Technology Corporation. Invention is credited to Saupama Das, William Walter.
Application Number | 20090108677 11/980182 |
Document ID | / |
Family ID | 40581923 |
Filed Date | 2009-04-30 |
United States Patent
Application |
20090108677 |
Kind Code |
A1 |
Walter; William ; et
al. |
April 30, 2009 |
Bidirectional power converters
Abstract
Circuits and methods for bidirectional power conversion are
provided that allow mobile and other devices to generate power
suitable to support multiple modes of operation. The bidirectional
power converters of the present invention may operate in both step
up and step down configurations rather than having a single
dedicated conversion function and use many of the same components
thereby reducing converter size and complexity.
Inventors: |
Walter; William; (Lowell,
MA) ; Das; Saupama; (Somerville, MA) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
Linear Technology
Corporation
|
Family ID: |
40581923 |
Appl. No.: |
11/980182 |
Filed: |
October 29, 2007 |
Current U.S.
Class: |
307/80 |
Current CPC
Class: |
Y02B 70/10 20130101;
H02M 3/1588 20130101; H02M 3/1582 20130101 |
Class at
Publication: |
307/80 |
International
Class: |
H02J 1/00 20060101
H02J001/00 |
Claims
1. A bi-directional power converter, which operates as a step down
converter in a first direction and a step up converter in a second
direction, comprising: one reactive element for storing energy when
operating in the first direction and the second direction; a
plurality of switching elements for selectively coupling the one
reactive element to one of two or more power sources; and mode
selection circuitry for selectively coupling the bi-directional
power converter to a first power source when operating as a step
down converter and to a second power source when operating a step
up converter, such that when the bi-directional power converter is
operating as the step up converter, the bi-directional power
converter is configured to deliver power to a communications link
that includes a power component.
2. The bi-directional power converter of claim 1 configured to
provide power to the communications link in compliance with the
universal serial bus On The GO specification when operating as a
step up converter.
3. The bi-directional power converter of claim 1 configured to
provide power sufficient to operate a mobile device when operating
as a step down converter.
4. The bi-directional power converter of claim 1 further comprising
a battery charging circuit.
5. The bi-directional power converter of claim 4 wherein the
battery charging circuit is used to regulate power provided to an
energy storage device when the bi-directional power converter
operating as a step down converter.
6. The bi-directional power converter of claim 1 further comprising
control circuitry coupled to the mode selection circuitry, the
control circuitry controlling the plurality of switches such that
the bi-directional power converter operates in either the step up
or step down mode in response to a mode selection signal provided
by the mode selection circuitry.
7. The bi-directional power converter of claim 6 wherein the
control circuitry controls the duty cycle of at least one of the
plurality of switches such that the bi-directional power converter
provides a desired regulated output voltage.
8. The bi-directional power converter of claim 1 wherein the mode
selection circuitry further comprises sensing circuitry.
9. The bi-directional power converter of claim 8 wherein the
sensing circuitry includes a comparison circuit.
10. The bi-directional power converter of claim 1 wherein the first
power source is a power adapter.
11. The bi-directional power converter of claim 1 wherein the
second power source is a battery of a mobile device.
12. A bi-directional DC to DC power converter, which operates as a
buck converter in a first direction and a boost converter in a
second direction, comprising: one reactive element for storing
energy when operating in either the first direction or the second
direction; a plurality of switching elements for selectively
coupling the one reactive element to one of two or more power
sources; and control circuitry controlling the plurality of
switches such that the bi-directional power converter operates in
either a buck mode or boost mode, such that when the bi-directional
power converter is operating as the boost converter, the
bi-directional power converter is configured to deliver power to a
communications link that includes a power component.
13. The bi-directional power converter of claim 12 configured to
provide power to the communications link in compliance with the
universal serial bus On The GO specification when operating as a
boost converter.
14. The bi-directional power converter of claim 12 configured to
provide power sufficient to operate a mobile device when operating
as a buck converter.
15. The bi-directional power converter of claim 12 further
comprising a battery charging circuit.
16. The bi-directional power converter of claim 15 wherein the
battery charging circuit is used to regulate power provided to an
energy storage device when the bi-directional power converter
operating as a buck converter.
17. The bi-directional power converter of claim 1 further
comprising mode selection circuitry coupled to the control
circuitry for selectively coupling the bi-directional power
converter to a first power source when operating as the buck
converter and to a second power source when operating as the boost
converter.
18. The bi-directional power converter of claim 17 wherein the
control circuitry controls the duty cycle of at least one of the
plurality of switches such that the bi-directional power converter
provides a desired regulated output voltage.
19. The bi-directional power converter of claim 17 wherein the mode
selection circuitry further comprises sensing circuitry.
20. The bi-directional power converter of claim 19 wherein the
sensing circuitry includes a comparison circuit.
21. The bi-directional power converter of claim 12 wherein the
first power source is a power adapter.
22. The bi-directional power converter of claim 12 wherein the
second power source is a battery of a mobile device.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to bidirectional power converters.
More particularly, the inventions described herein relate to
systems and methods for creating bidirectional power converters
that may be used to covert power in two different directions.
[0002] Power conversion circuitry may be found in virtually every
device that requires electricity. The purpose of power conversion
circuitry is to transfer electrical power from a power source to a
load, typically through certain conditioning and regulation
circuitry. A typical application of power conversion circuitry is
to convert AC power, provided by a power utility, to a regulated DC
voltage suitable for use with consumer electronics. Although power
conversion circuits are frequently implemented as stand alone
systems, often they are constructed as integrated circuits (ICs)
and used in various applications such as communications and
computing systems.
[0003] One type of commonly used power converter is a DC to DC
converter, which changes one DC voltage level to another. A step
down or buck converter, for example, provides an efficient way of
converting a higher DC voltage to a lower DC voltage, which is
desirable in certain electronic systems. A laptop computer, for
example, may have a battery supplying 12 volts DC and a processor
which requires 5 volts DC. A step down converter, implemented as an
IC with some external components, may be used to convert the 12
volt battery voltage to the 5 volts required by the processor with
minimal energy loss.
[0004] Another type of DC to DC converter is a step up or boost
converter. Such converters are used to increase the voltage
supplied from a source to a load. For example, an LED may require
3.3 volts DC to emit light. The LED may be powered by a single 1.5
volt battery through the use of a boost converter which may step up
the battery voltage to the level required by the LED. Boost
converters are also used to provide the higher voltages needed to
power fluorescent lights and cathode ray tubes.
[0005] In many instances, consumer electronic devices require the
use of both step up and step down voltage converters. A portable
communications device such as a cellular telephone or PDA is
typically battery powered and has a bright, multi colored display
screen. When the portable device, such as a BlackBerry, is
operating under battery power, the battery voltage used to drive
the display screen is stepped up through a boost converter. When
the device is plugged into a wall socket and its battery is
charging, the battery charging circuitry may rely on a buck
converter to step down the voltage, which provides the proper
charging voltage and increases current which charges the battery
more quickly.
[0006] Often a PDA or other portable communications device is
charged through the use of common interconnection link such as a
USB link. A BlackBerry, for example, may use the power provided on
the USB connection for both operating power and to charge its
battery. In this case, a buck converter is used to regulate the
supplied voltage, which is typically set to a value just above the
battery voltage in order to minimize power dissipation in the
charger and to maintain the current within USB specifications. An
example of such a device that accomplishes this task is the LTC
4088, manufactured by Linear Technology Corporation of Milpitas,
Calif., the assignee of this patent application.
[0007] Interconnection links such as a USB link, typically operate
in two modes. In a host mode or in a slave mode. When a device such
as a PDA is connected to a PC through a USB link, the PC acts as
the host and provides control functions that power and manage the
USB link. Conversely, the USB port in the PDA operates in the slave
mode and needs the PC to provide power and to supervise
communications so both devices can communicate with one
another.
[0008] In many instances, however, the USB link in the PDA or other
mobile device does not have the capability to operate in the host
mode and drive the USB link. Although the mobile device may have
the necessary controller circuitry to supervise USB communications,
it does not have the capability to provide the power required to
drive the USB link. This is often due to the relatively low voltage
provided by its battery and the inability of the mobile device to
convert that voltage to level suitable to drive the USB link. As a
result, if the mobile device is connected to a device which may
only operate as a USB slave, such as a memory stick, the mobile
device cannot power the USB link, preventing the devices from
communicating with one another.
[0009] Accordingly, in view of the foregoing, it would be desirable
to provide circuitry and methods for bidirectional power conversion
that allow mobile and other devices to generate power suitable to
support multiple applications.
SUMMARY OF THE INVENTION
[0010] Circuits and methods for bidirectional power conversion are
provided that allow mobile and other devices to generate power
suitable to support multiple modes of operation. The bidirectional
power converters of the present invention may operate in both step
up and step down configurations rather than having a single
dedicated conversion function and use many of the same components
thereby reducing converter size and complexity.
[0011] In one embodiment of the present invention, a bi-directional
power converter is provided, which operates as a step down
converter in a first direction and a step up converter in a second
direction and includes a reactive element for storing energy when
operating in the first direction and the second direction, a
plurality of switching elements for selectively coupling the one
reactive element to one of two or more power sources, and mode
selection circuitry for selectively coupling the bi-directional
power converter to a first power source when operating as a step
down converter and to a second power source when operating a step
up converter, such that when the bi-directional power converter is
operating as the step up converter, the bi-directional power
converter is configured to deliver power to a communications link
that includes a power component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The above and other objects and advantages of the present
invention will be apparent upon consideration of the following
detailed description, taken in conjunction with the accompanying
drawings, in which like reference characters refer to like parts
throughout, and in which:
[0013] FIG. 1A is a generalized block diagram of one embodiment of
a bidirectional power converter in accordance with the principles
of the present invention;
[0014] FIG. 1B is an illustrative embodiment of the bidirectional
power converter of FIG. 1A deployed in a mobile device;
[0015] FIG. 2 is a general schematic diagram of an embodiment of a
bidirectional power converter in accordance with the principles of
the present invention;
[0016] FIG. 3 is a more detailed schematic diagram of the
bidirectional power converter of FIG. 2;
[0017] FIG. 4 is a more detailed schematic diagram of the
bidirectional power converter of FIG. 2;
[0018] FIG. 5 is a more detailed schematic diagram of the
bidirectional power converter of FIG. 2 operating in a step
down/buck mode; and
[0019] FIG. 6 is a more detailed schematic diagram of the
bidirectional power converter of FIG. 2 operating in a step
up/boost mode.
DETAILED DESCRIPTION OF THE INVENTION
[0020] A general block diagram of one embodiment of a bidirectional
power converter constructed in accordance with the principles of
present invention is shown in FIG. 1A. As shown, system 10 includes
a bidirectional power converter which may operate in at least two
modes. Such modes may include a buck mode (i.e., step down) and
boost mode (i.e., step up). Converter 10 may switch from one mode
of operation to another depending on where an input signal is
applied. For example, converter 10 may operate as a buck converter
when a voltage V1 is applied across terminals 11 and 13 (in the
direction indicated by the top arrow). In this case, converter 10
steps down voltage V1 and produces a reduced output voltage V2 at
terminals 15 and 17. Conversely, converter 10 may operate as a
boost converter when a voltage V2 is applied across terminals 15
and 17 (in the reverse direction indicated by the bottom arrow). In
this case, the voltage is stepped up by converter 10 which produces
and an output voltage V1 of increased magnitude at terminals 11 and
13. Generally speaking, converter 10 operates in one of the two
modes at any given time.
[0021] In a preferred embodiment of the invention, converter 10
uses many (or all) of the same components in both the buck and
boost modes (described in more detail below). This is desirable for
several reasons, including the reduction in size and complexity of
the converter as well as eliminating the need to provide two
separate dedicated unidirectional converters, each requiring a
different set of components, to provide the same functionality. In
addition, the small size of converter 10 makes it ideal for
implementation as an integrated circuit and thus can be readily
deployed to mobile devices such as PDAs, mobile phones, digital
cameras, as a stand alone converter, and in other portable
rechargeable devices which require voltage conversion such as
flashlights, etc.
[0022] One application of converter 10 includes power conversion
suitable for use in driving various internal and/or external
applications of a mobile device. For example, in accordance with
one aspect of the present invention, converter 10 may be installed
on a mobile device 20 (such as a PDA) and used to perform two
conversion functions. A general illustration of this is shown in
FIG. 1B. One conversion function may be related to an application
that may be considered an "internal" application and another may
relate to what may be considered an "external" application
(although other combinations are possible, such as internal or
external only, multiple other conversion modes, etc.).
[0023] One internal application may include regulation of power
from and external source, such as directly from a wall socket or
through a commonly used communications link which has a power
component, such as a USB link. As shown in FIG. 1B, when connected
to external power source 23, converter 10 may operate in buck mode
and act as a voltage regulator to provide power to mobile device 20
and charge its battery (through link 33, which may be a
communications link, such as a USB link or any other suitable power
conduit). When the mobile device 20 is disconnected from external
power source 23, it relies on the battery to provide its power.
[0024] When mobile device 20 is operating on battery power,
converter 10 may also be used for certain external (or other
internal) applications that require a higher voltage level than
that provided by the battery. For example, the mobile device may be
coupled to an external device such as an audio speaker 24 that
requires voltage at a greater level than that provided by the
battery. In this case, converter 10 may act as a boost converter
and step up the battery voltage to provide the appropriate higher
voltage level to the external device through power link 32 (which
may be any suitable power conduit).
[0025] Another external application for converter 10 may include
the use of the boost function to provide the voltage necessary to
drive a communications link such as a USB port. For example, as
mentioned above, mobile device 20 may be coupled to an external
device which is a USB slave device, such as memory stick 26. In
this case, converter 10 may act as a boost converter and step up
the battery voltage from device 20 to provide the voltage necessary
to drive memory stick 26 through USB link 34. In some embodiments,
the amount of boosting may be programmable or selectable to
multiple different levels to support various different
applications. Thus, mobile device 20 may use converter 10
bi-directionally, i.e., to regulate inbound power and boost
internal battery voltage in the opposite direction for use with
other applications.
[0026] An example of one specific implementation involving a USB
bus, in accordance with an embodiment of the invention, includes
configuring converter 10 to comply with the USB "On The Go"
specification for driving and communicating with USB slave devices.
For example, converter 10 may be installed in a digital camera and
be used to drive its USB connection so it may couple to a memory
stick and transfer digital image files (not shown). In this case,
the camera, which is usually a slave device when coupled to a PC,
becomes the host device, and supplies power via the USB link to the
memory stick, and supervises communications. Thus, converter 10,
operating in the boost mode, may boost the camera battery voltage
such that it supplies a voltage between about 4.75 and 5.25 volts
with a rated current limit of about 500 mA to the power bus of the
USB link from the camera's battery. In cases where the slave device
requires less than about 100 mA, the lower voltage threshold may be
reduced to about 4.4 volts.
[0027] It will be understood from the foregoing that although the
power paths described above may include conventional power cables
and/or a communications link such as a USB link, that any other
suitable power conduit may be used, if desired. For example, other
communications links that use host/slave configurations may be used
such as FireWire (IEEE 1394), Ethernet (IEEE 802), etc. if desired,
and that converter 10 may be configured to provide the appropriate
voltage to drive such links. Moreover, converter 10 in device 20
may be configured such that it provides power to charge the battery
of a second mobile device rather than power a USB link (e.g.,
through a communications links rather than driving a communications
link (e.g., PDA to PDA, or PDA to digital camera through a
communications or power link, etc.)).
[0028] Furthermore, it will be appreciated that although the above
describes converter 10 as including buck and boost converters, any
other suitable DC to DC converters may be implemented in a similar
bidirectional configuration, including, but not limited to buck,
boost, buck-boost, inverting, flyback, push-pull, H-bridge, Cuk or
SEPIC configurations for bidirectional power conversion. In some
embodiments, it is desirable to construct converter 10 using
configurations that do not require a transformer to reduce size,
weight and/or cost.
[0029] One possible implementation of converter 10 is generally
illustrated as converter 100 in FIG. 2. As shown, converter 100
includes terminals 111, 113, 115 and 117, switches 102 and 104,
inductor 106, and capacitors 108 and 110. Voltage source 112
generally represents an external power source, such as an AC/DC
wall adapter or USB host, but may also represent an external load
such as a USB memory stick or other host application. Voltage
source 114 generally represents an internal power source, such as a
battery or other storage element. Source 114 can act as a load when
charging the battery, and act as a power source when providing
power to an external host application such as the USB memory stick
mentioned earlier. Typically, either voltage source 112 or voltage
source 114 are actively supplying power to converter 100 at any one
given time. Both are shown in converter 100 to provide a
comprehensive overview of the converter topology.
[0030] In some embodiments, buck/boost mode selection is determined
by a combination of user input and conditions on voltage source 112
and 114. If the user enables the converter to function as a buck
converter, (e.g., through a switch (not shown)) converter 100 will
operate as such if voltage source 112 is currently available.
Voltage source 114 may be present as a battery when buck mode is
enabled. converter 100 may be configured operate in a two or three
mode configuration. In a two mode configuration, converter 100 may
switch between buck and boost modes. In a three mode configuration,
converter 100 may switch between buck and boost mode and include a
standby mode when neither conversion mode is desired. Such
embodiments may employ two or three position switches,
respectively, with each switch position corresponding to an
operating mode.
[0031] If the user enables converter 100 to function as a boost
converter, it will operate as such provided that voltage source 114
is available and substantially no voltage is already present on
source 112. This prevents converter 100 from attempting to drive
terminals 111 and 113 when input power is already available.
However, in some embodiments, some voltage is permissible such as
the case where boost mode is used to charge battery 112, which is
not fully depleted.
[0032] In one embodiment, bidirectional converter 100 is intended
for use as a USB dual role device. Dual role devices may act as a
host or as a peripheral and can supply or receive power. The roles
may be determined by mode selection circuitry (not shown in FIG.
2). In some embodiments, the input of a user selectable switch as
described above.
[0033] In other embodiments, the mode of operation may be
determined by the type of connector that is connected converter 100
(e.g., in a device 20). For example, a USB cable for On-The-Go
applications may have a mini-A plug on one end and a mini-B plug on
the other. The USB device has a mini-AB receptacle and can mate
with either plug. The plugs typically contain an ID pin that
designates whether converter 100 will need to operate as a type A
device (power source) or a type B device (power sink).
[0034] If a mini-B plug is connected to terminals 111 and 113, the
ID pin will have a characteristic that allows the mode circuit to
select the proper mode of operation (e.g., a resistance greater
than 100 kOhms to ground). The mode selection circuitry then
configures converter 100 to operate as a step down converter and
provide power from source 112 to battery 114.
[0035] If, however, a mini-A plug is connected to terminals 111 and
113, the mode selection circuitry senses a different characteristic
on the ID pin (e.g., a resistance of less than 10 ohms to ground).
In this case, the mode circuit configures converter 100 to operate
as a step up converter and provide power to terminals 111 and
113.
[0036] In the first mode of operation, converter 100 may function
as a buck converter and convert a voltage applied by voltage source
112 to a lower level at terminals 115 and 117. When operating in
the buck mode, voltage source 114 may be coupled to converter 100
such that it absorbs and/or stores power from source 112, or, in
some embodiments, may be electrically disconnected from converter
100 (not shown). The resulting voltage generated across terminals
115 and 117 may be used to provide power to a mobile device and may
be coupled to a power bus for that purpose.
[0037] Assuming source 114 is coupled such that it stores or
absorbs power provided by source 112, converter 100 may operate as
follows. Generally speaking, voltage source 112 provides incoming
power such as rectified input voltage to converter 100. Switches
102 and 104 are controlled such that the converter alternates
between charging and discharging phases to provide a desired
voltage at terminals 115 and 117. For example, when switch 102 is
closed and switch 104 is opened, voltage source 112 is coupled to
inductor 106. This causes energy from voltage source 112 to be
stored on inductor 106 (i.e., a charging phase) and power to be
supplied to terminals 115 and 117 via the increasing current
through the inductor. When switch 102 is opened and switch 104 is
closed, energy stored on inductor 106 is transferred to the load at
terminals 115 and 117 (i.e., a discharging phase). By controlling
the duty cycle of the two switches (Time one switch is closed with
respect to the total time both switches are closed), the amount of
energy transferred to the load on terminals 115 and 117 can be
adjusted to provide a relatively smooth and regulated output
voltage at terminals 115 and 117.
[0038] Converter 100, however, may also operate in the reverse
direction as a boost converter. For example, assuming source 112
now represents the voltage bus of a communication link such as a
USB link or an external load such as a speaker, converter 100 may
operate as follows. Similar to the buck converter above, switches
102 and 104 are controlled such that the converter alternates
between charging and discharging phases to provide a desired
voltage. For example, when switch 104 is closed and switch 102 is
opened the load at terminals 111 and 113 is isolated from inductor
106 and energy from voltage source 114 is stored on inductor 106
(i.e., a charging phase).
[0039] When switch 104 is opened and switch 102 is closed the
energy stored in inductor 106 is provided to the load at terminals
111 and 113 (i.e., a discharging phase). In this switching
configuration the voltage at terminals 111 and 113 is greater than
that of the source 114. By controlling the duty cycle of the two
switches, the amount of energy transferred to the load on terminals
111 and 113 can be adjusted to provide a relatively smooth and
regulated output voltage at terminals 111 and 113.
[0040] There are several well known methods for controlling the
duty cycle of switching converter 100 to provide a regulated output
voltage such as Current-Mode control or Voltage-Mode control. In
either control method, the main switch (switch 102 in step down
mode, switch 104 in step-up mode) is turned ON at the beginning of
every period and the output voltage is connected to the inverting
terminal of an error amplifier while a reference is connected to
the non-inverting terminal (not shown).
[0041] In a voltage mode converter, the output of the error
amplifier is compared to a sawtooth ramp. When the ramp voltage
exceeds the error amplifier voltage the main switch turns OFF and
the synchronous rectifier (switch 104 in step down mode, switch 102
in step up mode) turns ON for the rest of the period. If the output
voltage is less than a reference voltage, the output of the error
amplifier increases, which in turn increases the duty cycle and
thus the output voltage. By adjusting the output of the error
amplifier the duty cycle of the main switch can be increased or
decreased to regulate the output voltage.
[0042] In current mode control, the output of the error amplifier
represents the desired inductor current and is compared to the
current through the main switch. When the main switch is on, the
inductor current is rising. When the inductor current rises above
the output of the error amplifier, the main switch is turned OFF
and the synchronous rectifier is turned ON for the rest of the
cycle. By adjusting the output of the error amplifier the inductor
current can be increased or decreased to regulate the output
voltage. In some cases a sawtooth ramp is added to the switch
current signal to eliminate a well known instability. The details
of these control methods can be found in many switching power
supply texts known in the art such as "Switching Power Supply
Design" by Abraham I. Pressman.
[0043] Thus, as can be seen from the above, a simple bidirectional
power converter which uses all (or virtually all) of the same
circuit components is provided. Converter 100 is useful for
multiple mobile and other applications.
[0044] One possible specific embodiment of converter 100
constructed in accordance with the principles of the present
invention is shown in FIG. 3 as converter 200. Converter 200
illustrates converter 100 operating in buck mode and thus certain
components associated with boost mode operation have been omitted
for simplicity.
[0045] Converter 200 is similar in many respects to the converter
shown in FIG. 2 and generally includes components and functional
blocks which have been numbered similarly to denote similar
functionality and general correspondence. For example, Converter
200 includes voltage source 212 (voltage source 112 in FIG. 2),
inductor 206 and capacitor 210 (inductor 106 and capacitor 110
respectively in FIG. 2), battery 214 (voltage source 114). PMOS
transistor 202 and NMOS transistor 204 (switches 102 and 104,
respectively in FIG. 2) and terminals 211, 213, 215, and 217
(terminals 111, 113, 115 and 117 in FIG. 2). Converter 200 also
includes control circuit 205, mode circuit 209 and may include
optional battery charger circuit 218 and diode 219.
[0046] In operation, converter 200 may be set to operate in buck
mode by an external signal (manual or automatic) and/or internally
by sensing signals at terminals 211 and 213 and 215 and 217 and
selecting the proper mode of operation (e.g., by comparing signals
at these terminals). This may be accomplished by mode circuit 209
which may include comparison, sensing or other circuitry used to
determine the appropriate mode of operation. As mentioned above,
one way this may be accomplished is by sensing conditions on an ID
pin at node 250. Converter 200 may also sense the voltage at node
211 through path 251 with mode circuit 209 to confirm the voltage
level is as expected based on conditions sensed at node 250. In
some embodiments, if the sensed voltage level at node 211 does not
agree with the conditions sensed at node 250, mode selection
circuitry 209 may place converter 200 in a standby state, or may
rely on the voltage measured at node 211 in making mode selection
decisions.
[0047] Once buck mode is selected, control circuit 205 generates
the control signals used to drive PMOS switch 202 and NMOS switch
204 such that converter 200 operates in buck mode. In some
embodiments, control circuit 205 may include control circuitry such
as pulse width modulation circuitry and drive circuitry suitable
for switching PMOS switch 202 and NMOS switch 204 ON and OFF.
[0048] Thus, in operation, control circuit 205 alternates converter
200 between charging and discharging phases to provide a desired
regulated output voltage across terminals 215 and 217. For example,
when control circuit 205 turns PMOS switch 202 ON, and NMOS switch
204 OFF, voltage source 212 is coupled to inductor 206. This causes
energy from voltage source 212 to be stored on inductor 206 and
power to be supplied to terminals 215 and 217 via the increasing
current through the inductor. When control circuit 205 turns OFF
PMOS switch 202 and turns ON NMOS switch 204 inductor 206
discharges and provide energy to battery 214, capacitor 210 and
terminals 215 and 217. In some embodiments, converter 200 may
include optional battery charging circuitry 218 and diode 219. The
charging circuitry 218 may be used to control the charging of
battery 214 when voltage source 212 is present to charge the
battery. The regulated voltage across terminals 215 and 217 may
also be further used to drive a load such as that associated with
powering a consumer electronic device. Optional diode 219 provides
current from the battery to supply system load across terminals 215
and 217 when voltage source 212 is not present or when the system
load exceeds current available from voltage source 212 when
present.
[0049] By controlling the duty cycle of the two switches, control
circuit 205 adjusts the amount of energy transferred to the load on
terminals 215 and 217 to provide a relatively smooth and regulated
output voltage at terminals 215 and 217 and to battery 214.
[0050] Optional battery charger 218 may further condition the
regulated voltage such that it also provides a substantially
constant current and constant voltage to battery 214 to facilitate
charging. Moreover, in some embodiments, converter 200 may include
sensing path 203, which may be used to monitor input current from
voltage source 212. Exceeding an input current threshold may cause
control circuit 205 to adjust the duty cycle of PMOS switch 202
until input current returns to below the threshold limit.
[0051] Referring now to FIG. 4, converter 300 is shown, which is a
representation of converter 200, operating in the opposite
direction in boost mode. Accordingly, certain components associated
with buck mode operation have been omitted for simplicity. Because
virtually all the same components are used and perform the same or
very similar function, the component designation numbers remain the
same.
[0052] As in converter 200, converter 300 may be set to operate in
boost mode by an external signal (manual or automatic) and/or
internally by sensing signals at terminals 211 and 213 and 215 and
217 and selecting the proper mode of operation (e.g., by comparing
signals at these terminals. This may be accomplished by mode
circuit 209 which may include comparison, sensing or other
circuitry used to determine the appropriate mode of operation. As
mentioned above, one way this may be accomplished is by sensing
conditions on an ID pin at node 250. Converter 300 may also sense
the voltage at node 211 through path 251 with mode circuit 209 to
confirm the voltage level is as expected based on conditions sensed
at node 250. In some embodiments, if the sensed voltage level at
node 211 does not agree with the conditions sensed at node 250,
mode selection circuitry 209 may place converter 200 in a standby
state, or may rely on the voltage measured at node 211 in making
mode selection decisions.
[0053] Once boost mode is selected, control circuit 205 generates
the control signals used to drive PMOS switch 202 and NMOS switch
204 such that converter 300 operates in boost mode. Control circuit
205 alternates converter 300 between charging and discharging
phases to provide a desired boosted output voltage across terminals
211 and 213. For example, when control circuit 205 turns PMOS
switch 202 OFF and NMOS switch 204 ON the load at terminals 211 and
213 becomes isolated from inductor 206 and energy from battery 214
is stored on inductor 206.
[0054] When control circuit 205 turns ON PMOS switch 202 and turns
OFF NMOS switch 204 the energy stored in inductor 206 is provided
to the load and produces a boosted voltage at terminals 211 and
213. The regulated voltage across terminals 211 and 213 may be used
to power a communications link, such as a USB link, and/or may be
further used to drive a load such an audio speaker, etc.
[0055] Moreover, in some embodiments, sensing path 203 may be used
by control circuit 205 to monitor the output current of converter
300. Exceeding an output current threshold may cause control
circuit 205 to adjust the duty cycle of NMOS switch 204 until
output current returns to below the threshold limit. For example,
such current sensing may be performed to ensure that the current
supplied is within the range specified by a communications link,
such as a USB link. In addition, it will be understood that while
in boost mode, battery 214 may be driving both converter 300 and
any associated load, such as consumer electronics.
[0056] Referring now to FIG. 5, converter 400 is shown, which is a
more detailed representation of converter 200 in FIG. 3, operating
in buck mode. In some embodiments, converter 400 may be disposed on
an integrated circuit 301. Converter 400 is similar in many
respects to the converter shown in FIG. 3 and generally includes
components and functional blocks which have been numbered similarly
to denote similar functionality and general correspondence. For
example, circuit 400 includes voltage source 312 (voltage source
212 in FIG. 3), inductor 306 and capacitor 310 (inductor 206 and
capacitor 210 respectively in FIG. 3), battery 314 (battery 214 in
FIG. 3), PMOS transistor 302 and NMOS transistor 304 (switches 202
and 204, respectively in FIG. 3), control circuit 305 (control
circuit 205), mode circuit 309 (mode circuit 209), optional battery
charging circuit 318 (charger 218) and terminals 311, 313, 315, and
317 (terminals 211, 213, 215 and 217 in FIG. 3). Converter 400 also
includes amplifier circuits 320, 322 and 324 and may further
include diodes 330 and 332.
[0057] In operation, converter 400, like converter 200, may be set
to operate in buck mode by an external signal (manual or automatic)
or internally by sensing signals at input/output terminals and
selecting the proper mode of operation. This may be accomplished by
mode circuit 309 to determine the appropriate mode of
operation.
[0058] For example, mode circuitry 309 may sense conditions at an
ID pin coupled to node 350 to determine whether to operate in buck
or boost mode. Assuming buck mode characteristics are sensed (e.g.
a resistance greater than 100 kOhms to ground on the ID pin), mode
selection circuitry 309 configures converter 400 as a buck
converter. In this case, mode circuit 309 connects the output of
amplifier 320 to control circuit 305 through switch 352. In some
embodiments, mode circuit 309 may disable or turn OFF amplifier 324
when converter 400 operates in buck mode.
[0059] Converter 400 may also sense the voltage at node 311 through
path 351 with mode circuit 309 to confirm the voltage level is as
expected based on conditions sensed at node 350. In some
embodiments, if the sensed voltage level at node 311 does not agree
with the conditions sensed at node 350, mode selection circuitry
309 may place converter 400 in a standby state, or may rely on the
voltage measured at node 311 in making mode selection
decisions.
[0060] In a USB embodiment, if a voltage greater than 4.3V and/or
greater than the battery is present on source 312, as determined by
a comparator in the mode selection circuitry 309, converter 400 may
automatically operate as a step-down converter and charge the
battery and provide power to terminals 315 and 317. In some
embodiments, an optional microcontroller or user can also use path
350 to adjust power settings, such of converter 400 such as between
100 mA and 500 mA modes for USB embodiments, or put converter 400
in standby through logic inputs to the mode selection circuitry
(not shown).
[0061] Once buck mode is selected, control circuit 305 generates
the control signals used to drive PMOS transistor 302 and NMOS
transistor 304 such that converter 400 operates in buck mode.
Although shown as PMOS and NMOS transistors, switches 302 and 304
may be implemented as any suitable semiconductor or armature type
switches with any suitable polarity or configuration. In the case
where switch 302 is a PNP power transistor, Schottky diodes may be
coupled in parallel to avoid transistor saturation in one or both
directions. Moreover, in some embodiments, control circuit 305 may
include control circuitry such as pulse width modulation circuitry
and drive circuitry suitable for switching PMOS transistor 302 and
NMOS transistor 304 ON and OFF.
[0062] In operation, converter 400 may receive a rectified input
voltage at terminal 311 from a wall socket or other power source.
Control circuit 305 operates in conjunction with amplifiers 320 and
322 and alternates converter 400 between charging and discharging
phases to provide a desired regulated output voltage across
terminals 315 and 317. When control circuit 305 turns PMOS
transistor 302 ON, and NMOS transistor 304 OFF, voltage source 312
is coupled to inductor 306. This causes energy from voltage source
312 to be stored on inductor 306 and power to be supplied to
terminals 315 and 317 via the increasing current through the
inductor.
[0063] When the control circuit 305 turns OFF PMOS transistor 302
and turns ON NMOS transistor 304 inductor 306 discharges and
provide energy to terminals 315 and 317. The current paths from
input 311 to inductor 306, via PMOS transistor 302, and from ground
to inductor 306, via NMOS transistor 304, are shown by the top most
dotted lines. Amplifier 320 compares the output voltage 315 of
converter 400 with a preset reference signal REF1.
[0064] If the output voltage is less than REF1, amplifier 320 will
provide an error signal that causes control circuit 305 to increase
the duty cycle of PMOS transistor 302 and provide more power to
terminals 315 and 317 until the output voltage is substantially
equal to REF1. If the output voltage is greater than REF1,
amplifier 320 will provide an error signal that causes control
circuit 305 to decrease the duty cycle of PMOS transistor 302 and
reduce power to terminals 315 and 317 until the output voltage is
substantially equal to REF1.
[0065] In embodiments that include optional battery charging
circuitry 318, charger 318 may further condition the output voltage
such that it also provides a substantially constant current and
constant voltage to output voltage 315 above the battery voltage
314 to facilitate charging. In this case the non-inverting terminal
of amplifier 320, connected to the battery 314, provides a
regulation point for the output voltage 315. The regulation point
of 315 is generally set slightly higher than the battery voltage to
allow correct operation of the battery charging circuitry 318.
[0066] Generally speaking, amplifier 320 will set the regulation
point based on the signals at both non-inverting inputs (e.g., will
regulate to the higher of the two applied voltages). The current
path from input 311 to battery 314 is generally shown by the
downward dotted line that passes through charger 318. Current flow
directly into the battery from inductor 306 is blocked by diodes
330 and 332. A suitable such charging circuit may be found in the
LTC 4088. In this operating mode, the regulated voltage across
terminals 315 and 317 may also be further used to drive a load such
as that associated with powering a consumer electronic device.
[0067] By controlling the duty cycle of the two switches, amplifier
320 generates an error signal that causes control circuit 305 to
adjust the amount of energy transferred to the load on terminals
315 and 317, providing a relatively smooth and regulated output
voltage at terminals 315 and 317. Moreover, in some embodiments,
converter 400 may include sensing path 303, which may be used to
monitor input current from voltage source 312 through resistor 340
(which is compared to the threshold set by REF2). Exceeding an
input current threshold may cause amplifier 322 to produce an error
signal that causes control circuit 305 to reduce the duty cycle of
PMOS transistor 302 until input current returns to below the
threshold limit. If the current drawn by the system at terminal 315
exceeds the current available from converter 400 due to input
current limiting, the battery will supply the difference through
internal diode 330 and external diode.
[0068] Referring now to FIG. 6, converter 500 is shown, which is a
more detailed representation of converter 300 in FIG. 4, operating
in boost mode. In some embodiments, converter 500 may be disposed
on an integrated circuit package 301. Converter 500 is similar in
many respects to the converter shown in FIG. 4 and generally
includes components and functional blocks which have been numbered
similarly to denote similar functionality and general
correspondence. For example, circuit 500 includes battery 314
(battery 214 in FIG. 4), inductor 306 and capacitor 310 (inductor
206 and capacitor 210 respectively in FIG. 4), PMOS transistor 302
and NMOS transistor 304 (switches 202 and 204, respectively in FIG.
4), control circuit 305 (control circuit 205), mode circuit 309
(mode circuit 209) and terminals 311, 313, 315, and 317 (terminals
211, 213, 215 and 217 in FIG. 3). Converter 500 also includes
amplifier circuits 320, 322 and 324 and may further include diodes
330 and 332.
[0069] In operation, converter 500, like converter 300, may be set
to operate in boost mode by an external signal (manual or
automatic) or internally by sensing signals at input/output
terminals and selecting the proper mode of operation.
[0070] For example, mode circuitry 309 may sense conditions at an
ID pin coupled to node 350 to determine whether to operate in buck
or boost mode. Assuming boost mode characteristics are sensed (e.g.
a resistance of less than 10 Ohms to ground), mode selection
circuitry 309 configures converter 500 as a boost converter. In
this case, mode circuit 309 connects the output of amplifier 324 to
control circuit 305 through switch 352. In some embodiments, mode
circuit 309 may disable or turn OFF amplifier 320 when converter
500 operates in boost mode.
[0071] Converter 500 may also sense the voltage at node 311 through
path 351 with mode circuit 309 to confirm the voltage level is as
expected based on conditions sensed at node 350. In some
embodiments, if the sensed voltage level at node 311 does not agree
with the conditions sensed at node 350, mode selection circuitry
309 may place converter 500 in a standby state, or may rely on the
voltage measured at node 311 in making mode selection
decisions.
[0072] In USB embodiments, mode circuit 309 may configure converter
500 to operate as a step up converter to power up terminals 311 and
313 provided that there sufficient battery voltage on terminals 315
and 317 (e.g., greater than about 2.8V for a typical single cell
LiIon battery). This can be determined using path 353 in
conjunction with a comparator in mode circuit 309. In some
embodiments, a microcontroller (not shown) or user can place
converter 500 in standby mode via path 350 and power down terminals
311 and 313. This may occur when the peripheral device no longer
needs power. If the peripheral device later needs power from
converter 500 it can request it from the microcontroller/user using
the Session Request Protocol (SRP). The microcontroller/user can
then re-enable the step-up converter through path 350.
[0073] To prevent accidental back-driving of an external input
supply on terminals 311 and 313 during boost mode, mode circuit 309
may determine if there is already more than about 4.3V on the
terminals when the ID pin has less than 10 ohms to ground. If such
voltage is already present, the mode circuit 309 will not enable
the converter. This case is possible if a mini-B plug with a faulty
ID pin is connected to terminals 311 and 313.
[0074] Although shown as PMOS and NMOS transistors, switches 302
and 304 may be implemented as any suitable semiconductor or
armature type switches with any suitable polarity or configuration.
In the case where switch 302 is a PNP power transistor, Schottky
diodes may be coupled in parallel to avoid transistor saturation in
one or both directions. Moreover, in some embodiments, control
circuit 305 may include control circuitry such as pulse width
modulation circuitry and drive circuitry suitable for switching
PMOS transistor 302 and NMOS transistor 304 ON and OFF.
[0075] In operation, converter 500 receives an input voltage at
terminal 315 from battery 314. Control circuit 305 operates in
conjunction with amplifiers 322 and 324 and alternates converter
500 between charging and discharging phases to provide a desired
boosted output voltage across terminals 311 and 313. For example,
when control circuit 305 turns PMOS transistor 302 OFF and NMOS
transistor 304 ON the load at terminals 311 and 313 becomes
isolated from inductor 306 and energy from battery 314 is stored on
inductor 306 (i.e., a charging phase). When control circuit 305
turns ON PMOS transistor 302 and turns OFF NMOS transistor 304 the
energy stored in inductor 306 is provided to the load and produces
a boosted voltage at terminals 311 and 313. The current path from
battery 314 to inductor 306 is shown by upward bound dotted lines
passing through diodes 330 and 332. Diodes 330 and 332 ideally have
a low forward voltage drop to minimize power loss. Though shown as
diodes, 330 and 332 may be implemented using MOSFETs and
comparators to more accurately approximate the "ideal diode"
function. The "Ideal diode" function described is practiced on the
LTC4088 manufactured by Linear Technology Corporation of Milpitas
Calif., the assignee of this patent application.
[0076] Amplifier 324 compares the output voltage of converter 500
with a preset reference signal REF3. If the output voltage is less
than REF3, amplifier 324 will generate an error signal that causes
control circuit 305 to increase the duty cycle of NMOS transistor
304 and provide more power to terminals 311 and 313 until the
output voltage substantially equals REF3. If the output voltage is
greater than REF3, amplifier 324 will generate an error signal that
causes control circuit 305 to decrease the duty cycle of NMOS
transistor 304 and reduce power to terminals 311 and 313 until the
output voltage substantially equals REF3. By controlling the duty
cycle of the two switches, amplifier 324 adjusts the amount of
energy transferred to the load on terminals 311 and 313 providing a
relatively smooth and regulated boosted output voltage at terminals
311 and 313.
[0077] The regulated voltage across terminals 311 and 313 may be
used to power a communications link, such as a USB link, and/or may
be further used to drive a load such an audio speaker, etc. The
current path from battery 314 to output terminal 311 is shown by
upward bound dotted lines passing through diodes 330 and 332,
through inductor 306 and PMOS transistor 302 to output terminal 311
(through filter capacitor 308). In this operating mode, the voltage
provided by battery may also be further used to drive a load such
as that associated with powering a consumer electronic device at
terminal 315.
[0078] Moreover, in some embodiments, converter 500 may include
sensing path 303 and amplifier 322, which may be used to monitor
the output current of converter 500 through resistor 340 (which is
compared to the threshold set by REF2). Exceeding an output current
threshold may cause amplifier 322 to reduce the duty cycle of NMOS
transistor 304 until output current returns to below the threshold
limit. For example, such current sensing may be performed to ensure
that the current supplied is within the range specified by a
communications link, such as a USB link.
[0079] Although preferred embodiments of the present invention have
been disclosed with various circuits connected to other circuits,
persons skilled in the art will appreciate that it may not be
necessary for such connections to be direct and additional circuits
may be interconnected between the shown connected circuits without
departing from the spirit of the invention as shown. Persons
skilled in the art also will appreciate that the present invention
can be practiced by other than the specifically described
embodiments. The described embodiments are presented for purposes
of illustration and not of limitation, and the present invention is
limited only by the claims which follow.
* * * * *