Versatile portable battery charging system protection scheme
Mobile devices are increasingly becoming an integral part of our daily life. Smart phones, for example, in addition to a simple phone call function, smart phones now also has a feature rich, social support network, web browsing, message sending, games, and a large high-definition screen can be used to. All of these features have made mobile phones a high power device. Battery capacity and energy density have been significantly improved to meet higher power demand. Charging 10 minutes to power a day for the equipment, while charging an hour to get 80% of the electricity, which has become the trend of high-end user experience. If the fast charging requirements and large battery capacity are combined together, the charging current of the portable device can reach 4A or even higher. This demand for high power supply to the battery power system design has brought many new challenges.
The utility model provides a portable battery charging protection circuit, including charging power supply, WS3206 chip, a processor and the lithium battery, the voltage input terminal of WS3206 chip and charge power supply is connected, the voltage output WS3206 chip end connected with a through a current sampling resistor and lithium batteries, voltage monitoring WS3206 chip terminal is connected through the voltage monitoring resistor with a lithium battery, connected signal input end of the processor and WS3206 chip, and processor and current sampling resistor connected. The utility model has the advantages of over voltage protection of the input voltage, over current protection of the battery over voltage, over current protection, over temperature protection, etc..
USB power supply
Portable devices usually use USB 5V power supply. Conventional USB port if the use of the USB2.0 specification, the maximum output current is 500mA, or if the use of USB3.0, the maximum output current is 900mA, which can not meet the requirements of the fast charging portable devices. USB adapter (dedicated charging port, that is, DCP) using the micro USB connection head can increase the output current to 1.8A. But unfortunately, the typical 5V/2A power adapter can only provide the total power of 10W. If you use this power adapter as a charger power supply, then the battery charger can only provide up to 2.5A of the charging current, and this is not enough to think that 4000mAh and a higher capacity of the battery pack fast charge. In order to improve the power, can we continue to increase the output current of the 5V Power Adapter? If we increase the cost and use a dedicated cable, it is theoretically possible. However, this approach will be subject to the following factors:
Higher adapter current (such as 2A or higher) requires a thicker cable and a dedicated USB connection head, which causes the system to increase the cost of the solution. In addition, due to the power loss and security issues to consider, the traditional USB cable can not fully meet the demand.
Depending on the length and diameter of the cable, the typical impedance of the adapter cable varies from 150 to 300mOhm. High adapter output current will cause the voltage drop of the whole cable, and then reduce the effective input voltage of the charger input. When the charger input voltage close to the battery charging voltage, the charging current will be significantly reduced, thereby prolonging the charging time.
In order to use the 5V/3A adapter for 180mOhm as an example, the voltage drop on the cable is 540mV. So the input voltage of the charger is 4.46V. We assume that the total resistance of the charger input to the battery pack is 150mOhm, which includes the charger power MOSFET of the DC resistance and the inductor resistance. Even if the charger can support the current 3A, but the 4.35V lithium ion battery charging, the maximum charge current is only 730mA. The charging current of less than 1A is obviously not high enough to meet the need of fast charging.
According to the above analysis, we must increase the input voltage of the power supply in order to provide sufficient voltage to avoid the charger into the low voltage drop mode. For these constraints, if the system requires more power than 10W or 15W, the best use of high voltage adapters, such as 9V or 12V. Under the same power, the high voltage adapter not only needs lower input current, but also has a greater input voltage margin. The only limitation of the high voltage adapter is the problem of backward compatibility. The high voltage adapter is inserted into a portable device for supporting the 5V input. If the system is not closed (due to over-voltage protection), the device will be damaged (due to the lack of adequate protection of the high voltage).
Due to the existence of these limiting factors, USD power supply adapter, and many other new hybrid high voltage adapter is flooding the market. The common characteristic of this kind of hybrid electric voltage adapter is that it can identify the system‘s voltage requirement by the handshake between the adapter and the system controller. The adapter to 5V as the starting output as the default value. Only when the system is confirmed to be able to support a higher voltage to achieve rapid charging, the voltage will be raised to a higher 9V or 12V. Communication between the system and the adapter can be achieved using VBUS, but also with a special handshake algorithm or signal to achieve through the D+ and D- lines. The new hybrid, adjustable voltage adapter can be used not only as a general power supply, but also as a conventional 5V voltage and a high input voltage system for fast charging.