【Repost】What is the basic principle of wireless charger? You will know after reading this
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Wireless charging has become popular after the release of the new generation of iPhone! Once, on the subway, I heard a little boy next to me say to the little girl: "I bought a wireless charger yesterday, and I can charge my phone by putting it on it. It's amazing!" So what is the basic principle of wireless chargers on the market? I hope this article can solve some confusion for many people who are already in the wireless charging industry or are preparing to enter the wireless charging industry. There are two tips before reading: This is not a popular science article, and some basic knowledge of electronics is required. If you are a salesperson in this field, you don't need to pursue the meaning of each noun, just understand the general logic. This article is not long. It only talks about pictures and answers four basic questions: 1. What are the components of wireless charging? The left side is TX, which is the transmitting end. The corresponding product is the wireless charging transmitter. The right side is Rx, which is the receiving end. The corresponding product is a mobile phone with wireless charging function. TX end: MCU, power full bridge, and LC resonant tank composed of inductor and capacitor, where the inductor is the transmitting coil. RX end: MCU, rectifier bridge, LDO, Charger chip, battery, and LC resonant tank, where the inductor is the receiving coil. 2. What is the power transmission path of wireless charging? The wireless charging transmitter inputs a DC voltage. The DC voltage passes through the power full bridge and generates an AC voltage at points SW1 and SW2, which is actually a square wave. The square wave is loaded at both ends of the LC Tank to generate an AC current. The AC current generates a magnetic field through the coil. The receiving coil senses this magnetic field and generates an AC current at the receiving LC Tank. The AC current is converted into a DC voltage through a rectifier bridge. The DC voltage then charges the battery through an LDO and a Charger. 3. What is the control circuit of wireless charging? In order to ensure the stability of the entire wireless charging system, VRECT needs to set a target voltage (Target Voltage) and control it through a feedback loop; in order to achieve high conversion efficiency, its value is usually set to be only slightly higher than LDO. The feedback loop will first collect the VRECT voltage and subtract it from the target voltage to generate an error signal (Control Error). The error signal will be transmitted to the MCU at the transmitter through the communication method specified by WPC, and the MCU will determine whether the receiver wants the transmitter to increase or decrease energy. MCU controls the energy of transmission by controlling three signals: input voltage power full bridge switching frequency power full bridge input duty cycle 4. What is the communication mechanism of wireless charging? The essence of conveying information is to change the signal. For example, if I wave to you and you see my hand changing, you know I am calling you. When the receiving end transmits information, a group of capacitors will be connected or disconnected on both sides of the LC Tank at the receiving end. The connection or disconnection of the capacitor will cause the equivalent impedance of the LC Tank at the transmitting end to change. The change in equivalent impedance will cause the current in the LC Tank at the transmitting end to change, and the voltage (Coil Voltage) at the connection between the capacitor and the inductor to change. This changing signal will be collected and demodulated, and transmitted to the MCU. The entire law of change is written in the WPC protocol. The MCU uses the WPC protocol to know what information the receiving end has told the transmitting end.
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