Rechargeable battery and stand-alone fast charger circuit diagram

Rechargeable batteries have become a standard power source for today's electronic products, especially portable devices: laptops, handheld navigators, mobile phones, etc. These products need to consume more and more power, and rechargeable battery capacity is not growing fast enough to meet their needs. The main reason for the increase in power consumption is the enhancement of device functions. The increase in power consumption of portable devices makes the use of rechargeable batteries cheaper and more environmentally friendly than standard batteries.

Stand-alone Ni-MH battery fast charger

The temperature and terminal voltage of a rechargeable nickel-metal hydride battery gradually increase as the battery is charged, and begin to decrease after the battery is fully charged. Therefore, the main task of the NiMH battery charger is to detect this mutation point and interrupt charging, or switch from fast charging to trickle charging. Additionally, continuous monitoring of temperature and voltage during charging provides system safety. DS2711/DS2712 charger has the above functions. Additionally, they can operate stand-alone and do not require a microcontroller or microprocessor monitoring. This series of products is specially designed for a single AA or AAA rechargeable battery , and is also suitable for two batteries connected in series or parallel. DS2711 adopts a linear control structure, and DS2712 adopts a switching control structure. To maximize operating time and conserve battery energy, these chargers have 4 charging modes: precharge, fast charge, float charge and trickle charge. In float charge mode, the charging rate is switched to a lower rate after the battery is fully charged.

In addition to the monitoring function, the DS2711/DS2712 charger also has an internal timer that sets the maximum charge time through an external resistor connected to the TMR pin. The fast charge time can be set from 0.5 to 10 hours. The float time has been set to half the maximum charging time (0.25 to 5 hours). In fast charging mode, if the maximum charging time is exceeded, the charger will switch from fast charging mode to float charging mode and reset the timer. The timer starts timing the float charge process, and if the predetermined float charge time is reached, the charger will switch from float charge mode to trickle mode.

VP1 and VP2 are used to monitor the voltage, and THM1 and THM2 are used together with the thermistor to monitor the temperature of the battery. TMR (timer) and RSNS (sense resistor) are used to set the charging time and charging current. Another feature of the DS2711/DS2712 is the ability to detect battery charging failures and alkaline primary batteries. If these conditions occur, the charger will shut down on its own.

Stand-alone lithium-ion battery fast charger

Because there is no need to detect the rate of voltage change (dV/dt), lithium-ion battery chargers are simpler than nickel-metal hydride batteries. At the same time, because lithium-ion batteries are very sensitive to overcharge, the charger requires a precise 4.2V±50mV power supply to ensure constant power charging. As for NiMH batteries, the charger not only requires voltage monitoring, but also other monitoring functions (temperature, timing, etc.).

The stand-alone lithium-ion battery charger MAX8601 has a built-in so-called Vbatt controllable voltage source, which can provide 4.2V±0.021V at +25℃, or provide 4.2V±0.034V accuracy at 40℃<85℃. When charging a lithium-ion battery through the VBATT connection, the charger can maintain constant output power (Figure 5), and an external resistor (to the SETI pin) and an external capacitor (to the CT pin) can set the charge current and internal timing. The charger also monitors the temperature of the battery through a negative temperature coefficient resistor.

The main advantage of the MAX8601 charger is that it can charge the battery via an external adapter or USB port. The USB port can provide 100mA and 500mA current according to the setting of the USEL pin. The chip automatically selects the external power source (main adapter or USB). If both power sources are present at the same time, it will select the main adapter for charging. Any power supply must be able to provide a minimum voltage of 4.5V. The DS2711/DS2712 and MAX8601 are stand-alone chargers with multiple monitoring functions (voltage, current, temperature , timing, etc.) that require neither microcontroller monitoring nor power surge protection, and provide clear and simple External switching.