Noty AN138fa Linear Technology
Wireless Power User Guide
Trevor Barcelo
Application Note 138
October 2013
OVERVIEW
An inductive wireless power system consists of a transmit
ter that generates a high frequency alternating magnetic
field and a receiver that collects power from that field.
The resonant coupled system described here provides for
increased power transmit distance and reduced alignment
sensitivity, with no need for a coupling core.
To build a wireless power system four items are required:
transmitter electronics, transmit coil, receive coil and
receiver electronics. The LTC4120 wireless synchronous
buck charger combined with minimal external circuitry
comprises the receiver electronics (Figure 1). Please see
the LTC4120 data sheet for more detail.
L, LT, LT C, LT M, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Figure 1. LTC4120 Receiver Demo Board
an138fa
AN138-1
Application Note 138
Figure 2. Implementation of Basic Transmitter Reference Design
Figure 3. Proxi-Point Transmitter Figure 4. Proxi-2D Transmitter
AN138-2
an138fa
Application Note 138
Transmitter Solutions
Currently there are four transmitter options available for
design or off-the-shelf purchase:
1. Basic: This wireless power design (Figure 2) was
developed by collaboration between PowerbyProxi
Inc. and Linear Technology. It is provided as an open
source reference design that can be used to integrate
the LTC4120 into a wireless power system. The details
of the push-pull current-fed resonant converter are
described later in this document.
2. Proxi-Point: This is an advanced transmitter (Figure 3)
that is available from PowerbyProxi. For further information visit www.powerbyproxi.com. It is ready to use
or incorporate directly into a product. Unlike the basic
transmitter, it offers features such as foreign metal detection, low standby power and a stable crystal-controlled
operating frequency. The transmit coil is built in.
3. Proxi-2D: This is an advanced transmitter (Figure 4) that
is available from PowerbyProxi. For further information visit www.powerbyproxi.com. It is ready to use or
incorporate directly into a product. Unlike Proxi-Point,
it is capable of charging multiple receivers simultaneously in any orientation on the 2D charging surface.
The transmit coil is built in.
4. Proxi Custom: If the above options are not suitable for
your application, a custom transmitter can be designed
and manufactured to meet your requirements. Please contact PowerbyProxi at info@powerbyproxi.com for further
information and pricing or visit www.powerbyproxi.com.
BASIC TRANSMITTER
The basic transmitter for the LTC4120, described in the
following sections, combined with a receive coil and
LTC4120-based receiver electronics can be used to
produce a wireless battery charging system. This wireless battery charging system enables evaluation of the
LTC4120 using standard components.
Basic is a resonant DC-AC transmitter. It is a simple, easy
and inexpensive transmitter designed to work with the
LTC4120. Pre-regulation is required to provide a relatively
precise DC input voltage to meet a given set of receive
power requirements. The basic transmitter does not feature
foreign object metal detection and can therefore cause
these objects to heat up. Furthermore, the operating fre
quency of the basic transmitter can vary with component
selection and load.
The system draws power from a DC power supply to wire
lessly charge multi-chemistry batteries. A block diagram
of the system is shown in Figure 5.
While the basic transmitter can be used to build a wire
less battery charging system, a Proxi-Point or Proxi-2D
transmitter is recommended for applications requiring
enhanced features as described in the Appendix.
-
-
-
DC POWER SUPPLY
COUPLING (TX + RX COIL)
R
X
LTC4120
CIRCUIT
an138 F05
TX CIRCUIT
Figure 5. Functional Block Diagram of Wireless Battery Charging System
TX COIL RX COIL
T
X
WIRELESS BATTERY CHARGING SYSTEM
BATTERY
an138fa
AN138-3
Loading...