1. High reliability: Especially for components like LED street light drivers, which are installed at high altitudes, maintenance is inconvenient and costly.
2. High Efficiency: LEDs are energy-saving products, so the driver power supply must be highly efficient. Heat dissipation is crucial for the power supply's junction within the lamp fixture. Higher power supply efficiency means lower power loss, less heat generation inside the lamp fixture, and a smaller temperature rise, which helps slow down LED light decay.
3. High Power Factor: Power factor is the requirement of the power grid for the load. Generally, there are no strict requirements for appliances under 70W. Although a low power factor for a single appliance with low power consumption has little impact on the power grid, the large amount of lighting at night and the excessive concentration of similar loads can cause serious pollution to the power grid. For 30W~40W LED drivers, there may be certain requirements for power factor in the future.
4. Driving Methods: Currently, there are generally two driving methods: ① One constant voltage source supplies multiple constant current sources, with each constant current source independently powering each LED. This method offers flexible combinations; if one LED fails, it does not affect the operation of other LEDs, but the cost is slightly higher. ② Direct constant current power supply, with LEDs operating in series or parallel. Its advantage is lower cost, but it lacks flexibility and requires addressing the issue of ensuring that the failure of one LED does not affect the operation of other LEDs.
5. Surge Protection: LEDs have relatively poor surge protection, especially against reverse voltage. Therefore, strengthening protection in this area is crucial. Some outdoor LEDs, such as LED streetlights, are susceptible to surges from the power grid due to load switching and lightning strikes. Some of these surges can damage the LEDs. Therefore, LED driver power supplies must have the ability to suppress surge intrusion and protect the LEDs from damage.
6. Protection Functions: In addition to standard protection functions, the power supply should ideally include LED temperature negative feedback in the constant current output to prevent the LED temperature from overheating.
7. Protection: For lighting fixtures installed outdoors or in complex environments, the power supply structure needs to be waterproof, moisture-proof, and heat-resistant;
8. Safety Regulations: LED driver power supply products must comply with safety standards and electromagnetic compatibility requirements;
9. Other: For example, the LED driver power supply needs to be matched with the LED lifespan, etc.
1. According to the driving method, they are divided into constant current type and constant voltage type.
1) Constant Current Type: The characteristic of a constant current circuit is that the output current is constant, and the output voltage varies with the load resistance. A constant current power supply is a relatively ideal solution for driving LEDs and is not afraid of short circuits in the load. The LED brightness is also more consistent. Disadvantages: High cost, the load cannot be completely open-circuited, and the number of LEDs should not be too large because the power supply has a maximum current and voltage capacity.
2) Constant voltage type: The characteristic of a constant voltage drive circuit is that the output voltage is constant, and the output current varies with the load resistance, so the voltage will not be very high. Disadvantages: It is forbidden to completely short-circuit the load, and voltage fluctuations will affect the LED brightness.
2. Based on circuit structure, it can be divided into capacitor step-down, transformer step-down, resistor step-down, RCC step-down, and PWM control type.
1) Capacitor step-down: LED power supplies using capacitor step-down are easily affected by mains voltage fluctuations, resulting in excessive inrush current and low power supply efficiency, but they have a simple structure.
2) Transformer step-down: This method has low conversion efficiency, low reliability, and the transformer is bulky.
3) Resistor voltage reduction: This method is similar to capacitor voltage reduction, except that resistors require more power, resulting in lower power efficiency.
4) RCC step-down type: This method is more widely used, not only because of its wide voltage regulation range, but also because its power efficiency can reach more than 70%. However, its load voltage ripple is relatively large.
5) PWM control: The PWM control method deserves special mention because, currently, LED power supplies designed with PWM control are quite ideal. The output voltage or current of this type of LED driver power supply is very stable, and the power conversion efficiency can reach 80% or even more than 90%. It is worth noting that this type of power supply can also be equipped with multiple protection circuits.
3. Based on whether the input and output are isolated, they can be divided into isolated and non-isolated types.
1) Isolated Topology: Isolation is for safety reasons, using a transformer to separate the input and output. Common topologies include forward, flyback, half-bridge, full-bridge, and push-pull. Forward and flyback topologies are mostly used in low-power applications, requiring fewer components and being simpler to implement. Among them, the flyback topology has a wide input voltage range and is often combined with PFC. Its application is more widespread, especially the flyback isolated driver.
2) Non-isolated: Isolated drivers are generally powered by batteries, storage batteries, or regulated power supplies, and are mainly used in portable electronic products, mining lamps, automobiles and other electrical equipment.
