Circuit analysis of wireless charger

Wireless charging has entered reality from dream and turned from concept to commodity. In recent years, it has led a new trend in mobile phones, electric vehicles and other fields. It proves that wireless charging technology has a very broad market prospect. The following is a micro distance wireless charger circuit scheme. This scheme is a feasibility exploration experiment. Then, let's learn about the circuit analysis of the wireless charger scheme!
Scheme and principle of wireless charger
The wireless charger scheme converts DC into high-frequency AC, and realizes the wireless power supply through the mutual inductive coupling between the primary and secondary coils without wired connection. The basic scheme is shown in the figure.
The wireless charger is composed of power transmitting circuit, power receiving circuit and charging control circuit.
Power transmission department
The power supply of the transmitting unit of the wireless charger scheme includes 220V AC and 24V DC, which are selected by the relay J. According to the principle of AC priority, the normally closed contact of relay J in the figure is connected with DC (battery BT1). Usually S3 is on.
When AC power is supplied, the rectified and smoothed DC adsorption relay J of about 26V acts in the form of AC power supply, the DC power supply BT1 is disconnected from the power transmission circuit, and LED1 (green) emits light to indicate its state.
The 24V DC power selected by the relay J is mainly supplied to the transmitting coil L1. In addition, it is supplied to the integrated circuit IC2 after being depressurized by IC1 (78l12). Therefore, in order not to make the action of J affect the stable action of the transmitting circuit, the capacitance of capacitor C3 must be more than 2200uf
The wireless transmission of power is actually realized through the mutual inductance of transmitting coil L1 and receiving coil L2, in which L1 and L2 constitute the primary and secondary coils of coreless transformer. In order to ensure sufficient power and as high efficiency as possible, it is appropriate to select a high modulation frequency and consider the high-frequency characteristics of the equipment.
Generally, the distance between the receiving coil L2 and the transmitting coil L1 is only a few centimeters, which is close to coaxial, so high transmission efficiency can be obtained. The principle of charging control circuit unit is shown in Figure 2-3.
The effective value of 1.6mhz sine wave voltage induced by L2 is about 16V (no-load). After bridge rectification (composed of four 1N4148 high-frequency switching diodes) and C5 filtering, about 20V DC is obtained. As the power supply of the charging control unit.
As the prototype of the feasibility exploration experiment, the wireless charger scheme is only for small capacity lithium-ion batteries and lithium polymer batteries of about 100mah. It is suitable for pocket digital products such as MP3, MP4 and Bluetooth headset. There are no obstacles in principle to popularize it into high-capacity batteries. Of course, from laboratory prototypes to market products, there may be long and arduous work such as electromagnetic radiation leakage, cost control and product technology, market entry and consumption start.
The above is the circuit analysis of the wireless charger scheme. For more information, please feel free to contact us!