Brief description of 18650 battery 3500mah lithium circuit design and electrical performance

　　The arrangement of the LEDs and the specification of the LED light source determine the basic driver requirements. The main function of the LED driver is to limit the current flowing through the LED within a certain range of operating conditions, regardless of changes in the input and output voltages. The most commonly used method is to use a transformer for electrical isolation. The article discusses factors that need to be considered in LED lighting design.

　　1. General requirements for LED drivers

　　Driving LEDs faces many challenges. For example, the forward voltage will change with changes in temperature and current, and the forward voltage of LEDs from different individuals, different batches, and different suppliers will also be different; in addition, the color point of the LED It will also drift with changes in current and temperature.

　　In addition, multiple LEDs are usually used in applications, which involves the arrangement of multiple LEDs. Among various arrangements, driving a single string of LEDs in series is preferred because this method provides excellent current matching performance regardless of how the forward voltage changes or how the output voltage (Vout) drifts.

　　Of course, users can also use other arrangements such as parallel, series-parallel combinations, and cross-connections for applications that require matching LED forward voltages and gain other advantages. For example, in a cross connection, if one of the LEDs is open due to a fault, the driving current of only one LED in the circuit will be doubled, thereby minimizing the impact on the entire circuit.

　　The arrangement of the LEDs and the specification of the LED light source determine the basic driver requirements. The main function of the LED driver is to limit the current flowing through the LED within a certain range of operating conditions, regardless of changes in the input and output voltages. The basic working circuit diagram of the LED driver is shown in Figure 2. The so-called isolation means that there is no physical electrical connection between the AC line voltage and the LED (i.e. input and output). The most commonly used method is to use a transformer for electrical isolation instead of Isolation does not use high-frequency transformers for electrical isolation.

　　It is worth mentioning that in LED lighting design, the AC-DC power conversion and constant current drive circuits can adopt different configurations:

　　1) Integral configuration, that is, the two are integrated and located within the lighting fixture. The advantages of this configuration include optimizing energy efficiency and simplifying installation;

　　2) Distributed configuration, that is, the two exist separately. This configuration simplifies security considerations and increases flexibility.

　　According to different application requirements, the LED driver can use constant voltage (CV) output, that is, the output is a clamped voltage under a certain current range; it can also use constant current (CC) output, and the output design can strictly limit the current; or Constant current and constant voltage (CCCV) output operation may be used, that is, constant output power is provided, so the forward voltage of the LED as a load determines its current.

　　Generally speaking, LED lighting design needs to consider the following factors:

　　Output power: involves LED forward voltage range, current and LED arrangement, etc.

　　Power supply: AC-DC power supply, DC-DC power supply, directly driven by AC power supply

　　Functional requirements: dimming requirements, dimming method (analog, digital or multi-level), lighting control

　　Other requirements: energy efficiency, power factor, size, cost, fault handling (protection characteristics), standards to be followed and reliability, etc.

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