FEAT RE FEA ATURE


COVER


COVER STORY


CHARGING A BATTERY WITHOUT A CONNECTOR – MADE EA Y


S TonyArm trong, director of product m rketing, pow ke


Tony Armstrong, director of productmarketing, pow r products at Linear Technology Corporation explores the latest capabilities for designing a wireless pow r charging system


ower products at Linear Technology explores the l test capabi ties for designi g a w rel ss power charging system


conductor is placed into this time-varying field a current is induced.


,


One common occurrence in electronic systems is electrical transients such as lightning strikes froman external source or capacitor discharge,which could be an internal repetitive disturbance such as in the condenser discharge of an ignition system. Themagnetic field intensity is


proportional to themagnitude of the current flowing in the conductor. Energy is transferred froma conductor that produces the fields (the primary) to any conductor o n which the fields impinge (the secondary) via themagnetic coupling defined above. In a loosely coupled systemwhere the


coupling coefficient is low, a high frequency current does not pass for long distances along a conductor but rapidly loses energy because of the impedancemismatch along the cable, which causes the energy to be reflected back to the source or radiated into the air. Figure 1 shows a graphical


ots of products use a battery as the primary power source. Of course, we all know about the “i-something” products with the fruit logo on them. However, there are plenty of less glamorous products that serve equally deserv applications that also use


L


batteries. I am rving


talking about portablemedical devices, industrial sensors and even rotating or moving equipment. Unlike the benign consumer environment, these applications havemore stringent requirements such as the need for sterilisation and even the potentially explosive surroundings like those commonly found in oil refineries and chemical processing facilities. Inmany of these applications, a connector for charging purposes is


difficult or impossible to use. For example, some products require sealed enclosures


wireless charging capable A wireless charging solution adds value, reliability n these applications s cannot .


.


where connecto r and robustness i


WIRELESS POWER TRANSM SSION So if wireless charging is a good solution in those instances where a connector cannot be used, what is it and how is it accomplished? Well, a simple and straightforward definitionmight be: wireless power is the transmission of electrical energy froma power source to an electrical load without the use ofman- made conductors.


WIRELESS POWER ANSMISSIONI


However, this tends to be a little too simplistic to demonstrate the challenges involved in performing this process. Therefore, I wish to provide you with a more in-depth explanation before we


to protect sensitive electronics fromharsh move onto the constraints andmethods environments. Othersmay simply be too small to include a connector; and in products where the batte ry-powered application includesmovement or


start with the ba to overcome the


rotation, it is virtually impossible to have charging with wires.


Therefore, what alternativemethod can be employed to deal with these


circumstances? Well, it is clearly one that eliminates the connector and would be


12 JUNE 2016 12 JUNE 2016 || ELEC RO ELECTRONICS CS


flowing throug h a conductor such as a wire, carries electrical energy. When an electric current passes through a circuit (or wire) there is amagnetic field in the area surrounding the conductor. In a circuit with alternating current,


mare discussed. So, let’s sics: an electric current ,


Linear TiL near Te Technology’s echnology’s


LTC4120 wireless power receiver and batter harger integrates technology by


PowerbyProxi, Linear’s technology partner


owerbyProxi, Linear’s technology partner


LTC4120 wireless power receiver and battery charger integrates technology by


representation of loosely coupledwindings connected via amagnetic field It should b e noted that this figure also shows the LTC4120, whichwill be discussed inmore detail later in this article.


. When designing a wireless power


charging system, a key parameter is the amount of charging power that actually adds energy to the battery. This received power depends onmany factors, including the amount of power being transmitted, the distance and alignment between the transmit coil and the receive coil als o known as the coupling between the coils, and finally the tolerance of the transmit and receive components.


The primary goal in any wireless power design is to guarantee delivery of the required power under worst-case power transfer conditions. However, it is equally important to avoid thermal and electrical overstress in the receiver during best- case conditions. This is especially important when output power


there exists a time-varyingmagnetic field in the vicinity of the wire; and if a


requirements are lo w. Take for exampl e when the battery is fully charged or nearly fully charged and the coils are in close proximity to each other. In such a scenario, available power fromthe wireless systemis high, but demanded power is low. This excess power typically leads to high rectified voltages or a need


/ ELECTRONICS ELECTRONICS


CHARGING A BATTERY WITHOUT A CONNECTOR – MADE EASY


gy Corporation


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