USB chargers， PD chargers , and PD power adapters are ubiquitous in our lives, mainly used to charge our electronic devices, which mostly use lithium-ion batteries. Lithium batteries are currently widely used, with the ability to be repeatedly used and recharged; they are the ideal energy source for portable electronic devices. Compared with other batteries, lithium batteries have the following characteristics:
High output voltage: the open circuit voltage is usually 3.6V, while the open circuit voltage of nickel-cadmium batteries and nickel-metal hydride batteries is 1.2V.
Large storage capacity: The characteristics of lithium batteries are their high energy density and large energy storage capacity. With the same output power, the volume and weight of lithium batteries are not only half lighter than nickel-metal hydride batteries, but also 20% smaller in size.
Discharge rate: The charging speed of lithium batteries is very fast. It only takes 1-2 hours to fully charge and reach the maximum energy state. At the same time, the leakage of lithium batteries is minimal. Even if they are left idle for 10-60 days and then used again, they can still provide power and work normally. The self-discharge rate of lithium batteries is low, less than 8%/month, far lower than the 30% of nickel-cadmium batteries and 40% of nickel-metal hydride batteries.
Lithium batteries have no “memory effect”, so they can be charged without decreasing their capacity when not fully discharged. However, if a lithium battery is overcharged after fully charged, it will damage the battery.
During the charging process of lithium batteries by USB chargers or PD chargers, the battery’s voltage and charging current will change with the charging time. Charging lithium batteries requires controlling their charging voltage, limiting charging current, and accurately detecting battery voltage. The charging characteristics of lithium batteries are completely different from those of nickel-cadmium and nickel-metal hydride batteries. Lithium batteries can be charged at any point during their discharge cycle, and can very effectively maintain their charge, with a longer retention time than nickel-metal hydride batteries. They are also lightweight, with a weight only half that of nickel-cadmium batteries of the same capacity, and have a mass density four times higher than nickel-cadmium batteries. When lithium batteries begin to charge, the voltage rises slowly, while the charging current gradually decreases. When the battery voltage reaches around 4.2V, the voltage basically remains unchanged, while the charging current continues to decrease.
The method for determining whether a lithium battery is fully charged is to use an ammeter to detect its charging current, and end the charging when the charging current drops to a certain value, such as when the charging current of a lithium battery drops to 30mA (around 5% of the initial charging current). Also, the battery voltage can be measured, with charging ending after a delay of 10-20 minutes after reaching 4.2V. Typically lithium batteries come with a high-precision battery protection board or voltage detection circuit to prevent overcharging, and their charging voltage should not exceed 4.25V.
Post time: May-31-2023