1. Wide voltage input and low voltage dimming.
The voltage input range of LED driver with LYTSwitch-7 IC is 90V to 305V, and dimming can still be realized under low voltage input. At this time, some people will ask, why not do high input voltage dimming? Of course, there is no problem to realize high voltage input technically, but any country has a single voltage, either low voltage, such as Japan and the United States, or high voltage, such as China and Europe, so positioning LED drivers at high voltage or low voltage can meet the needs of users. However, in some countries, such as the United States, the lighting market is divided into commercial and civil, and the power supply voltage of commercial lighting is often high voltage input, so it has dimming function without high voltage input. LYTSwitch-7 LED driver IC can not only cope with wide voltage input range, but also realize low voltage dimming, and realize wide voltage input under the condition of keeping the output current unchanged. So it can meet the needs of commercial and civil lighting in the United States at the same time.
2. Integrated protection, higher security.
In the driving scheme of separation module, if you want to increase certain protection, you need to add more equipment to realize it. The circuit protection of PI is fully integrated. This has three advantages. First of all, in the case of input overvoltage surge, input overvoltage protection can protect LED load. For example, when the circuit encounters lightning, as long as there is lightning in the circuit, high voltage will appear on the bus, and the IC will stop the switching operation accordingly, and the LED lights behind will avoid the high voltage hazard; Second, it provides protection against output overcurrent, overvoltage (OVP), short circuit and open load. For example, when the load is open, the voltage will continue to rise, and the capacitor at the load end will be easily damaged, and the output overvoltage protection can protect the output capacitor in this fault situation. Thirdly, when the driver is overheated, the output current decreases, and finally the thermal return protection is completely closed. For example, when a building is on fire, with the increase of ambient temperature, the LED lights will not go out immediately, but the brightness will gradually dim, thus giving people inside a chance to escape. As shown in figure 1, what is even more amazing is that when the temperature reaches a higher level, the lamp will be completely extinguished, and once the outside temperature returns to the normal range, the lamp will automatically resume lighting.
Figure 1: advanced thermal management performance-the bulb can still provide lighting output under abnormal ambient temperature.
3. Three factors determine that EMI is very low and compatible with most SCR dimmers.
EMI is a problem faced by all dimming driver schemes. It is not only related to the cost of EMI filter components, but also related to the compatibility of SCR dimmer connected to the front end. The LED driver using LYTSwitch-7 has low EMI. Mainly from the following three reasons: First, the "quiet" source node (source potential) is used for heat dissipation. Because of its special MOSFET technology, the heat dissipation mode of IC in this scheme is through the source, but in the circuit structure with buck type and switch tube at the lower end, the potential of MOSFET source does not change with its switch, so it is a low noise node in electricity and EMI will be very low; Second, work in a critical mode. Because the inductor current works in critical conduction mode, its working frequency is constantly changing. Noise energy is distributed in different frequency points, so its EMI will be relatively low; Thirdly, the switch tube is located in the low-end circuit structure, which can increase the copper area of the source and reduce the copper area of the drain on the PCB board, which not only ensures the heat dissipation of the IC itself, but also takes into account EMI.
Low EMI can not only save the cost of EMI filter, but also help drivers to be compatible with most SCR dimmers in the market, thus improving the compatibility of lamps.
4. The unique algorithm can provide high power factor and accurate adjustment rate.
Figure 2: Inductor current distribution
How to realize accurate constant current control is a problem that many LED driver IC manufacturers have been considering. As shown in fig. 2, in order to achieve high power factor, the current of the switching tube usually changes with the waveform of the input voltage. However, once any noise and low-frequency disturbance appear at the input end, it will appear on the LED driving current at the output end with the response of the switching tube current, which will cause the response change of illumination brightness and affect people's visual experience. LYTSwitch-7 power integration scheme adopts current-limiting mode in a half-wave period, that is, the peak current of the inductor does not change with the input voltage, so the input noise can be suppressed, and the current at the output is insensitive to the input noise. The situation that the output lighting is influenced by AC power supply is avoided. The control of output constant current is realized by keeping the average value of inductance current in AC half-wave. Therefore, its constant current accuracy can be guaranteed under different input voltages, loads and mass production conditions. In addition, compared with the traditional control method, the peak current is relatively low, the utilization rate of MOSFET is high, and the energy storage inductance can also be reduced. In addition, the unique power supply mode of the scheme itself does not need to attach a coupling winding to the inductor, so a low-cost commercial standard inductor can be used. This greatly increases the attraction of the scheme. (Bian Xiao: Shenzhen Junhongsheng Electronics)