• Classification of LED driver power supply

1. According to the driving mode, it is divided into constant current type and constant voltage led driver

a) Constant current type: The characteristic of the constant current type circuit is that the output current is constant, and the output voltage changes with the change of the load resistance. The constant current type power supply to drive the LED is an ideal solution and is not afraid of the load short circuit, and the LED brightness is consistent. Disadvantages: The cost is expensive, the load is completely open-circuited, and the number of LEDs should not be too many, because the power supply has a maximum withstand current and voltage.

b) Constant voltage type: The characteristic of constant voltage driving circuit is that the output voltage is constant, the output current changes with the change of the load resistance, and the voltage will not be very high. Disadvantages: It is forbidden to completely short-circuit the load, and voltage fluctuations will affect the brightness of the LED.

2. According to the circuit structure, it is divided into capacitor step-down, transformer step-down, resistor step-down, RCC step-down, PWM control type

a) Capacitive step-down: The LED power supply adopting the capacitive step-down method is easily affected by the fluctuation of the grid voltage, the impact current is too large, and the power supply efficiency is low, but the structure is simple

b) Transformer step-down: This method has low conversion efficiency, low reliability, and heavy transformer;

c) Resistive step-down: This method is similar to the capacitive step-down method, except that the resistor needs to consume more power, so the power supply efficiency is relatively low;

d) RCC step-down type: This method is more widely used, not only because of its wide voltage regulation range, but also its power utilization efficiency can reach more than 70%, but its load voltage ripple is relatively large;

e) PWM control type: I have to mention the use of PWM, because for now, the LED power supply designed by PWM control method is ideal. The output voltage or current of this LED driving power supply is very stable, and the power conversion The efficiency can also reach 80%, or even more than 90%. It is worth noting that this power supply can also be equipped with multiple protection circuits.

3. According to whether the input and output are isolated, it can be divided into isolated and non-isolated

a) Isolation type: Isolation is to isolate the input and output through the transformer for safety. Common topologies include forward, flyback, half-bridge, full-bridge, and push-pull. Forward and flyback topologies are mostly used in low-power applications, with few devices and simple operation. Among them, the flyback has a wide input voltage range and is often combined with PFC. Its more widely used is the flyback isolation driver.

b) Non-isolated: Isolated drivers are generally powered by batteries, storage batteries, and regulated power supplies, and are mainly used for portable electronic products, miner's lamps, automobiles, and other electrical equipment

• The importance of LED driver

Itt is difficult to supply LEDs with normal power due to the steep forward volt-ampere characteristics of LEDs. so It cannot be directly powered by a voltage source like an ordinary incandescent lamp, otherwise the voltage fluctuation will increase slightly, and the current will increase to the extent that the LED will be burned. In order to stabilize the working current of the LED and ensure the normal and reliable operation of the LED, various LED drive circuits with "ballast function" have emerged as the times require. The simplest is to connect a ballast resistor in series, while the more complicated one is a "constant current driver" composed of many electronic components.

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