In the eyes of modern people, mobile phones have long become an indispensable tool in life, and the advent of smart phones is even more popular in the past. High-power and high-power chargers for smartphone screens are naturally indispensable. Today, I will explain the principle of smart chargers. At present, rechargeable batteries have the characteristics of large discharge current and long service life. They are widely used in a variety of electronic products. When used together, the charging process is different for the same different batteries. Here is a detailed explanation about this problem.
Different batteries should use different charging control techniques. Commonly used control techniques include: negative voltage increment control, time control, temperature control, high voltage control technology, etc. Among them, the voltage negative increment control is one of the more advanced control methods recognized at present. When charging, when a negative increase in battery voltage is measured, it can be determined that the battery has been fully charged, thereby converting the charging to trickle charging. Time controls the predetermined charging time. When the charging time is reached, the charger stops charging or turns to trickle charging. This method is safer. The temperature control method is that when the battery reaches a full state, the battery temperature rises faster, and the battery temperature or temperature change is measured to determine whether to stop charging the battery. The high voltage control judges the charging state according to the allowable voltage of the rechargeable battery. This method is more flexible. This article introduces a smart charger that can charge nickel-cadmium batteries (Nicd), nickel-hydrogen batteries (NiMH) and lithium-ion batteries, and has the ability to automatically detect rechargeable batteries.
Charger design ideas
When designing a universal smart charger, it is necessary to fully consider the charging characteristics of the three kinds of batteries, and give different charging modes and corresponding algorithms for the characteristics of each battery.
Ni-MH/Ni-Cd battery charging mode
These two kinds of nickel batteries have similar charging characteristic curves, so the same charging algorithm can be used. The main charging control parameters of these two types of batteries are -ΔV and temperature θ.
The criterion for the conversion of Ni-MH/Ni-Cd battery from pre-charge to standard charge is: ①The voltage level of a single cell is 0.6～1V; ②The battery temperature is -5～0C. The criterion for battery saturation charging is: ①The battery voltage drops or Close to zero growth-ΔV= 6～15 mV/cell; ②High battery temperature θmax>50℃; ③Battery temperature rise rate dθ/dt ≥1.0℃/min. Because temperature changes are easily affected by the environment, the actual variables used to distinguish each stage of charging are mainly -ΔV, θmax, and the detection of -ΔV requires sufficient A/D resolution and current stability. -ΔV The measurement and A/D resolution, the stability of the charging current and the internal resistance of the battery have the following relationships: when the internal resistance of the battery is equal to 50Ω (close to saturation charging), the charging current = 1200mA, the current drift is equal to 5%, a single cell battery The charging voltage is 1.58V, and the battery voltage change caused by the current drift is 3mV.
Li-ion battery charging mode
When the lithium ion battery is charged and sampled, the measured voltage is the online voltage of the battery. Generally, the online voltage is higher than the static voltage (related to the internal resistance). In the charger design, the measurement of the conversion judgment for each stage of the lithium ion battery charging The only parameter is online voltage, and the voltage sampling deviation is less than 0.05 V.