Wireless Power Rectifier Overvoltage Protection via Transistor Inversion
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Solution Overview
Problem
Conventional wireless charging systems are inadequate in protecting devices from overvoltage situations, especially when power transfer exceeds 20 W, leading to excessive device operating temperature and potential malfunction due to insufficient impedance modification.
Innovation Solution
A wireless power receiving circuit with a transistor-based rectifier and control logic that compares the rectified output voltage to a reference voltage, asserting control signals to turn on all transistors simultaneously when an overvoltage is detected, thereby increasing impedance and reducing power reception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the inputs of the rectification circuit are shorted to ground to reduce impedance, then the rectifier receives less power, but the impedance modification is insufficient when power transfer exceeds 20 W, leading to excessive device operating temperature
Solution Approach 1:
Instead of shorting the inputs to ground (conventional approach), the patent connects the inputs to a voltage source that matches the safe operating voltage. This inversion of the conventional approach creates a much larger impedance mismatch, dramatically reducing power transfer to safe levels while avoiding excessive temperature rise.
Solution Approach 2:
The patent changes the impedance parameter by connecting to a voltage source with specific voltage characteristics rather than ground. This parameter change (from 0V ground connection to matched voltage source connection) creates sufficient impedance modification to reduce power transfer below 20W to safe levels, preventing overheating.
2Power
If the rectification circuit impedance is reduced by shorting inputs to ground, then power transfer is limited, but the impedance modification is a function of switch on-resistance which is insufficient for high power applications
Solution Approach 1:
The patent inverts the conventional grounding approach by connecting to a matched voltage source instead. This inversion creates far greater impedance modification effect, making power transfer limitation effective even at high power levels while ensuring reliable overvoltage protection.
Solution Approach 2:
The patent introduces a matched voltage source as an intermediary between the rectifier inputs and ground. This intermediary provides the appropriate impedance characteristics to effectively limit power transfer, serving as a mediator that achieves both power limitation and reliable protection.
3Reliability
If conventional overvoltage protection is used with switching to ground, then some protection is provided, but excessive power is still dissipated in the switches due to insufficient impedance modification
Solution Approach 1:
Instead of switching to ground (conventional), the patent switches to a matched voltage source. This inversion dramatically increases impedance modification, reducing power dissipation in the switching elements while maintaining effective overvoltage protection.
Solution Approach 2:
The patent converts the harmful effect of power dissipation in switches into a beneficial impedance matching effect. By connecting to a matched voltage source rather than ground, the switching elements experience much lower power dissipation while the impedance mismatch provides effective protection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces received power by approximately 6 dB compared to prior art designs, providing robust overvoltage protection and preventing device malfunction.
Implementation Method 1
a transmitter system 12 powers a primary coil 13 with alternating current, resulting in an oscillating magnetic field at the primary coil 13. A secondary coil 19 in a receiver 18 placed in proximity to this primary coil 13 will resonate with the field due to magnetic coupling between the primary coil 13 and secondary coil 19, leading to a corresponding alternating current in the secondary coil 19 according to Faraday's law of induction.
Implementation Method 2
By rectifying the alternating current in the secondary coil 19 using a rectification circuit within a power pick-up unit 20, output power DC power can be produced for use in powering a load 21.
Data Source
AI summary
A wireless power receiving circuit includes a transistor based rectifier receiving an AC input voltage, and control logic receiving an overvoltage signal. The control logic generates control signals for controlling turn on of transistors within the transistor based rectifier based upon the overvoltage signal so as to cause the transistor based rectifier to produce a rectified output voltage from the AC input voltage. A comparator compares the rectified output voltage to a reference voltage and asserts the overvoltage signal if the rectified output voltage is greater than the reference voltage. In response to assertion of the overvoltage signal, the control logic asserts the control signals to simultaneously turn on all transistors of the transistor based rectifier.