Design of smart charger hardware for lithium ion battery

Lithium-ion batteries have high energy weight and energy-to-volume ratio, no memory effect, many times of re-charging, long service life and lower price. A good Battery Charger gives the battery a long life. The intelligent charger designed by C8051F310 single-chip microcomputer has high measurement accuracy, can control the magnitude of charging current, adjust in time, and can judge the charging time according to the state of charging, and terminate charging in time to avoid the battery passing. Charge.

This article discusses the use C8051F310 device Lithium Ion Battery Charger's design. Generating a PWM pulse width modulation using software-controlled charging Power Supply, charging current required to accommodate the different stages. The temperature sensor monitors the battery temperature and detects the battery charging voltage and current through AD conversion and related calculations to determine which stage the battery reaches. Make the Li-ion Battery Charger have a longer life and a more efficient charging method.

designing process

1 charging principle

The characteristics of the battery uniquely determine its safety performance and efficiency of charging. The best way to charge a battery is determined by the chemical composition of the battery (lithium, nickel, nickel, or SLA ). Still, most charging solutions include the following three phases:

● Low current regulation stage

● Constant current stage

● Constant voltage stage / charge termination

All batteries are charged by transferring energy to themselves. The maximum charging current of one battery depends on the rated capacity of the battery ( C ). For example, a battery with a capacity of 1000mAh can charge 1C when the charging current is 1000mA . (1 times the battery capacity) can also be used 1 / 50C (20mA) or less current to charge the battery. However, this is just a normal low current charging method and is not suitable for fast charging solutions that require short charging times.

Most chargers in use now charge both the low current charging method and the rated charging current, that is, volume charging, which is usually used in the initial stage of charging. At this stage, the initial self-heating effect of the chip, which will cause the termination of the charging process, is minimized. Volume charging is usually used in the intermediate stage of charging, and most of the energy of the battery is stored at this stage. In the final stage of battery charging, most of the charging time is usually consumed at this stage, and the value of current, voltage or both can be monitored to determine when to end charging. Similarly, the end scheme relies on the chemistry of the battery. For example, most lithium-ion battery chargers keep the battery voltage at a constant value while detecting the lowest current. Nickel-cadmium and NiCd batteries use a rate of change in voltage or temperature to determine the end time of charging.