There are many varieties of LED electronic display products, but their common features are that they must use a DC power supply and a low operating voltage of a single device, and a conversion circuit must be used when using the city power. For different use cases, there are different solutions in the technical realization of the LED power converter.

According to the power supply voltage, LED drivers can be divided into three categories: one is battery-powered, mainly used for portable electronic products, driving low-power and medium-power white LEDs; the other is power supply greater than 5, which is powered by a stabilized power supply or a battery Power supply, such as step-down, step-down and step-down DC converters (converters; the third is directly powered by mains (110V or 220V) or corresponding high-voltage direct current (such as 40~400V), which is mainly used for camel high power White LED, such as step-down DC/DC converter.

1. Battery-powered drive scheme

The battery supply voltage is generally 0.8~1.65V. For low-power lighting devices such as LED displays, this is a common use case. This method is mainly suitable for portable electronic products to drive low-power and medium-power white LEDs, such as LED flashlights, LED emergency lights, energy-saving desk lamps, etc. Considering that it is possible to work with a AA battery and have the smallest volume, the best technical solution is a charge pump boost converter, such as a boost DC Zhuang (converter or boost (or A few of the charge pump converters of buck-boost type are drivers that use LDO circuits.

2. High voltage and dry driving scheme

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

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

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

When using the mains power to drive the LED, it is necessary to solve the problem of voltage reduction and rectification, but also to have a relatively high conversion efficiency, a smaller volume and a lower cost. In addition, the issue of security isolation should be resolved. Taking into account the impact on the power grid, electromagnetic interference and power factor issues must also be resolved. For medium and low power LEDs, the best circuit structure is an isolated single-ended flyback converter. For high-power applications, bridge conversion circuits should be used.

For LED driving, the main challenge is the non-linearity of the LED display. This is mainly reflected in the fact that the forward voltage of the LED will change with current and temperature, the forward voltage of different LED devices will be different, the “color point” of the LED will drift with the current and temperature, and the LED must be within the requirements of the specification. Work within the range to achieve reliable work. The main function of the LED driver is to limit the current under working conditions, regardless of changes in input conditions and forward voltage.

For the LED drive circuit, in addition to constant current stabilization, there are other key requirements. For example, if you need to perform LED dimming, you need to provide PWM technology, and the typical PWM frequency for LED dimming is 1~3kHz. In addition, the power handling capacity of the LED drive circuit must be sufficient, powerful, able to withstand a variety of fault conditions, and easy to implement. It is worth mentioning that because the LED is always at the optimum current and will not drift.

In the selection of LED display drive schemes, the inductance boost DC/DC was considered in the past. In recent years, the current that the charge pump driver can output has risen from a few hundred mA to 1.2A. Therefore, these two The output of the type of actuator is similar.