Wireless Power for the Mass Market

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Wireless charging is predicted to experience huge growth over the next few years. Currently the vast majority of wireless charging applications are accomplished over quite short distances, but in the future they will operate over much longer distances, and also direct the power automatically to target devices that require charging. Longer ranges and directional tracking will open new applications and bring many benefits to users. For example, in the medical field, wireless charging could be used to power implants inside the patient’s body. Device manufacturers have been hesitant to use rechargeable batteries in critical applications as patients have shown that they can be forgetful when it comes to charging. Automatically charging those implants as the patient goes about his or her business will allow rechargeable batteries in devices that can be full implanted inside the body. Usually these devices, such as heart pacemakers are implanted just under the patient’s skin for easier access to replace batteries. However, there are a few barriers to overcome before the technology gains widespread adoption. For example, if a metallic object comes between the charger and the device being charged, it can heat up. EMI from distributing relatively large amounts of power could also interfere with other devices in range.

Renesas is claiming that the company has made advances in wireless charging technology that solves some of these issues. It talked about those advancements at the International Solid-State Circuits Conference (ISSCC) in San Francisco, February 19-23. In the paper, Renesas presented the company's single-chip wireless power transmitter solution, claiming that it was the first that measures AC and DC transmitter power. This technique allows transmitted power to be measured more accurately, and detects any mismatch between the power transmitter (PTx) and the power receiver (PRx) power levels. It also is capable of detecting metallic objects directly between the transmitter and receiver. The presentation also included details of a new transmitter technology that features adaptive Zero-Voltage Switching (ZVS) to reduce EMI and provide higher power transmission efficiency, allowing wireless power transmission up to 15W with a Qi PRx and up to 40W with proprietary PRx solutions.

Adaptive ZVS ensures that the power MOSFETs switch after their drain-source voltage has dropped to 0V, reducing switching losses and increasing efficiency. The adaptive ZVS technology operates over wide load conditions and is ideal for half-bridge inverters powering varying loads. ZVS technology also reduces EMI by lowering the amount of energy that is converted into electromagnetic noise. When compared to the conventional methods, using ZVS decreases EMI by 4 decibel (dB) and can increase the PTx efficiency by 1.7% or more.

ZVS also helps extend the operational life of power systems in many applications by auto-calibrating the initial threshold of the comparator. Additionally, the system has a highly programmable PWM generator, which controls the transmitter power delivery characteristics to ensure that the device being charged receives the right amount of power. This improves the accuracy and stability of the charging process and provides more control over the delivered power.

The technical enhancements presented at ISSCC have been applied to some of Renesas’ wireless power transmitter ICs that are available today.

http://renesas.com/wirelesspower