18650 battery

Entry-level CCR charging solution for rechargeable 18650 battery

Since the trickle charger device is eliminated, the CCR-based charging circuit shown here supports major battery technologies. This CCR-based charging circuit can be implemented in a variety of applications, from AAs used every day in a home environment to portable devices and portable power tools. Background Rechargeable 18650 battery are widely used in portable electronic devices such as mobile phones, tablets, MP3 players, and digital cameras as a necessity in daily life in modern society. OEMs can more effectively support the functions of their devices by charging these 18650 battery efficiently to showcase products that provide longer service life and improved user experience. As a result, OEMs will gain a competitive advantage and become a larger market. How to use CCR (Constant Current Regulator) devices to create a low-power, low-cost, high-efficiency charging solution for rechargeable 18650 battery that covers a variety of applications. The charger (to prevent the battery from being affected by long-term operating damage) (to not feel uncomfortable every time the user is charged), to optimize the rate at which the charging process is carried out, such as to terminate the process It should play an important role in battery charging. By implementing a simple controller mechanism, you can terminate these charges in a timely manner. Types of Chargers Chargers can use continuous DC or pulsed DC power schemes. Before each system output there is a constant level that is maintained throughout the charging period and does not change, which does not affect the total charge that has entered the battery. Instead, a trickle-type expression will be filled step by step for lower capacity 18650 battery such as those in more widely used mobile devices is commonly used. The capacity of a battery in one hour is expressed as C. To further illustrate this, consider a battery with a rated current of 800μAh. If this battery were to be charged at 0.5C, a charging current of 400μA would be required for 2 hours. Battery Technology In addition to the C value, the charging current required for a rechargeable battery depends on the technology on which the battery is based. Each technology currently in use has properties that are more suitable for specific types of applications. The most commonly used rechargeable battery technologies include: Nickel Metal Hydride (NiMH) – This is a very high storage capacity compared to other technologies, allowing higher levels of charge to be stored in a smaller battery. Nickel Cadmium (NiCad) – Has a longer life and lower self-discharge levels than NiMH. NiCad is the lowest cost battery production method of the three technology options. Lithium Ion 18650 battery – Suitable for outdoor applications and is a way to create lightweight 18650 battery that operate at lower temperatures. This technology requires a relatively short charging time and can handle more charging cycles than alternative technologies such as NiCad or NiMH. Simple Charging Solution A typical charging circuit is shown in Figure 1. The circuit consists of a voltage reference, power supply, LED indicator, controller, and CCR. NiMH 18650 battery have a nominal voltage of 1.2V/cell and should be charged to 1.5V~1.6V/cell. There are several different techniques that can be used to decide when to end charging. These include peak voltage detection, negative delta voltage, delta temperature (dT/dt), temperature thresholds, and timers. High-end chargers can combine all of these together. CCR chargers use a peak voltage detection circuit that terminates the charging process when a predetermined peak voltage is reached. This peak voltage is 1.5V per cell, allowing the battery to be charged to about 97% of its maximum capacity. NiCad 18650 battery work in much the same way, so they can be charged in the same way. The charging cycle for lithium-ion 18650 battery is more complicated. Common practice here is to charge the battery at 4.2V/cell between 0.5V and 1C charge capacity, followed by a trickle charge. During the charging process, the temperature rise of lithium-ion 18650 battery should be kept below 5°C. If the temperature rises above this value, it indicates a potential for fire. The highest battery temperature is in the trickle charge portion of the charge cycle, where the risk of ignition is highest. Typically, some type of smart IC is used to monitor and control the battery charge to prevent this risk. Simple Charging Circuit Let's first discuss the different parts of the charging circuit. Battery Calculation Formula A comparator is used to compare the battery voltage to Vref. Connected to the inverting input is the battery voltage. To avoid oscillations in the comparator, hysteresis is added to the setup to improve system performance, which is achieved by placing the feedback resistor Rh between the output and the non-inverting input. The 1.0kΩ resistor R3 is used to make the ratio of R3 to Rh as simple as possible. By adjusting Rh, the hysteresis loop bandwidth can be varied. Increasing Rh means narrowing the bandwidth, and decreasing Rh means increasing the bandwidth. The bandwidth of the hysteresis loop must be greater than 200mV because the battery voltage will drop slightly after charging is completed (see Figure 3). The formula for calculating the high and low voltages at the inverting input is: Battery Calculation Formula Figure 4 shows the details of the entire charging circuit. These include the PNP transistor, NPN transistor, comparator, programmable precision reference voltage, and Q4 and Q5 in parallel with the two CCRs. Q4 and Q5, connected in parallel, are used to regulate the current. It is also possible to connect two or more CCRs in parallel within the charging circuit to achieve all the necessary currents. Two bipolar junction transistors (BJTs), Q3 and Q6, are used as switches to control the charging current. The base of Q6 is controlled by the comparator output through a 5.6kΩ resistor R6. The collector of Q6 is connected to the base of Q3 through a 1.0kΩ resistor R5. When the comparator output goes low, Q6 turns off and Q3 turns off, thus terminating the charging current. An LED is connected in series with Q7 to indicate that the battery is charging and to provide continuous current. This state turns off when the battery is fully charged. In recent electronic system designs, engineers are striving to develop products that are more energy-efficient and more reliable while limiting power consumption. Reducing the input voltage is one way to improve circuit performance. Therefore, a low VCE(sat) transistor and a low VF Schottky diode are included in the charging circuit. The power dissipation level is very important for the operation of the CCR. When all voltages drop across the CCR, the battery is charged with a continuous current, which, as already discussed, leads to an increase in the temperature of the CCR. When the device begins to float, the current decreases until it reaches a stable point. To minimize the temperature rise of the CCR, many of the voids found on the circuit board are covered with copper. The cathode of the CCR is connected to this copper area for heat dissipation. Note that when multiple CCRs are used in parallel, the power consumed by the individual CCRs is not the total charging current, but the voltage multiplied by the current through the CCR. Figure 5 shows the power dissipated by the CCR over time. The charging circuit shown in Figure 4 can be used to set a programmable precision reference suitable for Vref. The battery voltage and Vref are connected to the comparator inputs. When the battery voltage is below Vref, continuous current is delivered to the battery through the CCR. When the battery voltage equals Vref, charging is complete. This circuit design recommends the use of the TL4313 terminal programmable shunt regulator and LM311 comparator from ON Semiconductor. By eliminating the trickle charge during charging, the need to include a smart IC (for lithium-ion battery technology) is eliminated. This helps keep the battery in a safe operating area and prolongs its life. Since the trickle charger device is eliminated, the CCR-based charging circuit detailed here can be used with all major battery technologies (NiCad, NiMH, Li-ion). In this way, CCR-based charging circuits are implemented in many applications (supporting a wide range of charging currents), from AAs used every day in a home environment to portable devices and portable power tools. Application note AND9031 from ON Semiconductor provides detailed circuits and operating results.

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