LED electronic display screens have a wide variety of products, but their commonality is that they must use a DC power supply and a low working voltage of a single device. When using mains power, conversion circuits must be used. For different usage situations, there are different schemes for the technical implementation of LED power converters.

According to the level of power supply voltage, LED drivers can be divided into three categories: one is powered by batteries, mainly used in portable electronic products to drive small and medium power white LEDs; The second is the power supply that is greater than 5, powered by a regulated power supply or battery, such as a step-down or step-down DC converter; the third is directly powered by a mains supply (110V or 220V) or corresponding high-voltage DC power (such as} 40-400V), mainly used for driving high-power white LEDs, such as step-down DC/DC converters.

1. Battery powered drive scheme

The battery power supply voltage is generally 0.8~1.65V, which is a common use case for low-power lighting devices such as LED displays. This method is mainly applicable to portable electronic products, driving small and medium power white LEDs, such as LED flashlights, LED emergency lights, energy-saving desk lights, and so on. Considering that it is possible to work with a No. 5 battery and have a minimum volume, the best technical solution is a charge pump boost converter, such as a boost DC converter or a boost (or boost) charge pump converter, with a few drivers using LDO circuits.

2. High voltage dry sum driving scheme

The low-voltage power supply scheme with a voltage higher than 5 uses a dedicated regulated power supply or battery to supply power to the LED. The voltage supplied to the LED is always higher than the voltage drop of the LED tube, that is, always greater than 5V, such as 6V, 9V, 12V, 24V, or higher. In this case, it is mainly powered by a regulated power supply or battery for driving LED lights. This power supply scheme must solve the problem of power supply voltage reduction. Typical applications include solar lawn lamps, solar garden lamps, and lighting systems for motor vehicles.

3。 Drive scheme directly powered by mains or high-voltage direct current

This solution is directly powered by mains power (100V or 220V) or corresponding high-voltage DC power, and is mainly used to drive high-power white LED lamps. Mains power drive is a power supply method with the highest price ratio for LED displays, and it is the development direction for the popularization and application of LED lighting.

When using mains power to drive LEDs, it is necessary to solve the problems of voltage reduction and rectification, as well as to have higher conversion efficiency, smaller volume, and lower cost. In addition, the issue of security isolation should be addressed. Considering the impact on the power grid, electromagnetic interference and power factor issues should also be addressed. For medium and small power LEDs, the optimal circuit structure is an isolated single ended flyback converter. For high-power applications, bridge converter circuits should be used.

The main challenge for LED drivers is the nonlinearity of LED displays. This is mainly reflected in the fact that the forward voltage of LEDs varies with current and temperature, and the forward voltage of different LED devices varies. LED "color dots" drift with current and temperature, and LEDs must operate within the range required by the specifications to achieve reliable operation. The main role of LED drivers is to limit current under operating conditions, regardless of input conditions and forward voltage changes.

For LED driver circuits, there are other key requirements besides constant current and current stabilization. For example, if LED dimming is required, PWM technology needs to be provided, and the typical PWM frequency used for LED dimming is 1 to 3 kHz. In addition, the power processing capability of LED driver circuits must be sufficient and powerful, capable of withstanding multiple fault conditions, and easy to implement. It is worth mentioning that LEDs are always in a state of non drift at the most suitable current.

In the selection of LED display screen drive schemes, it was previously believed that inductive boost DC/DC drives have increased the output current of charge pump drivers from a few hundred milliamperes to around 1.2A phase in recent years. Therefore, the output of these two types of actuators is similar.