The design procedure of receiver coil of wireless charger

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The design procedure of receiver coil of wireless charger

When we don't understand wireless charging, we will naturally feel that it must be a very complex project. In fact, this is not the case. We just need to make a wireless charging transmitting coil and a wireless charging receiving coil to create a simple wireless charging environment. Now we can try it. The basic design steps of the receiver coil of the wireless charger are as follows.

(1) confirm the need for Wireless charger reception.

(2) understand the limitations of physical design: xy and Z size limits of the coil; estimate the interface clearance.

(3) select the following parameters: the power required by the load; the expected coupling coefficient between TX and Rx coils; the allowable space of Rx coils.

(4) use the circuit to run the simulation under the best condition of receiving the positioning.

(5) display the load line curve and judge whether the curve is acceptable.

(6) create a receiving coil characteristic specification that can be sent to the magnetic component supplier; create RX user BOM.

(7) build and test the prototype on a tester designated by Ti.

(8) end of coil design.

Shielding materials

The wireless charger changes from 220V power supply to a sympathetic electromagnetic field, and then the sympathetic electromagnetic field generates a sympathetic electromagnetic field, and then the sympathetic electromagnetic field changes to current charging; when the sympathetic electromagnetic field encounters metal, it will produce electronic eddy current, which will produce skin effect on the metal, generate heat energy on the metal, reduce the charging efficiency and waste electric energy. And the interference to the main board of the line affects the normal operation of the whole charger. With ferrite sheet (thickness 0.4-0.6mm), the permeability can reach up to 800. Through high magnetic flux, it can provide a circuit for the sympathetic magnetic field, which can improve the efficiency.

Shielding materials have two main functions:

(1) provide a low impedance path for magnetic flux, so that there are very few energy lines that can affect surrounding metal objects.

(2) use less turns to realize a higher inductance coil to reduce the coil resistance (the more turns, the higher resistance).

Thick shielding materials that absorb a large amount of magnetic flux (they have high flux saturation points) can be used to prevent the material behind the RX coil from heating up. When TX or RX with calibration magnet is encountered, the efficiency of thick shielding material is less affected than that of thin shielding material.

Manufacturers such as Vishay, TDK, Panasonic, E & E, elytone and mingstar can all provide typical shielding materials, which can help minimize efficiency degradation.

Please note that high conductivity ferrite materials (e.g. iron powder, etc.) are not always better than gapped materials. Although ferrite materials have high magnetic conductivity, the saturation point of flux is low when the thickness of shielding material decreases. This factor must be carefully considered.