Typical offline applications include electronic ballast, fluorescent lamp replacement, traffic light, LED light bulb (cheap LED lights), streets and parking lighting, building lighting, mark etc. The development of LED is very quickly, now from 100L/W to the 120L/W white LED can be mass produced. From the most left in the drive for input part, there are two important parts: one is power conversion, including the isolation type and isolate type two; another is the drive, it will input voltage conversion ChengHeng flow to drive leds. So, not only can improve efficiency, still can simplify the circuit.
Showing is the basic structure of LED driver. Need explanation is, if 230V ac line with another for an optional transformer, the converter can provide up to 19W (NCP1014) or 25NCP1028) power. In addition, in the output part, but also increased the constant-current circuits and highest voltage control circuit. Among them, NCP1014LED drives are completely isolated communication - dc converter, applications for constant current optimized. However, the development of LED drive also exist great challenges, because the LED itself is linear elements, so at present mainly are faced with the problem is: the first, positive voltage with current and temperature changes; Second, different device of positive voltage difference; Third, "color dot" will with current and changes of temperature and drift; Fourth, LED must be work within the scope of specification requirements, so as to Membrane/ Diaphragm Filter Presses Manufacturers achieve reliable work. NCP1014 is a section offline pulse width modulation (PWM) switching voltage regulators, has integrated high voltage MOSFET, when using universal ac line power supply, the highest 8W output power can provide. In addition to the current limit besides, making drive products, we also want to consider its efficiency, cost, size, and many other factors. Drive main function is working conditions within the confine current; no matter how input conditions and forward voltage changes. In figure 3 applications, with NCP1351 coupled with a new MOSFET, making a drive, it can support the constant-current 350mA to 1A.
Using NCP4300A's constant voltage circuit which has the following advantages: electric voltage measurement for influenza is only 20% of the simple division way; Through the stabilized higher accuracy, load of less than 3 percent, and according to the component tolerance between the different; Has special voltage stabilizer and stabilized loop, can go to the lavatory to designers design parameters; Only in the biggest positive voltage exceed 36V need plug-in and using zener to steady pressure for NCP4300A.
Onsemi company NCP1014/28 off-line second-generation LED driver circuit diagram (wholesale LED christmas lights), among them, the blue part is the constant current circuit, also has the highest voltage stifle the circuit, ensure output voltage won't exceed design, and ensure the safety voltage range.
At present, the most common white LED is made by wiping yellow phosphorus in blue light-emitting diode.
In some more powerful applications, such as the design of more than 15W, common single chip drives will have power limits, so consider using discrete method to implement. In efficiency in the visual system, because the person can filter out the current ripple frequency, so if the switching frequency reach to 100Hz-150Hz, the "constant", the drive for dc current wouldn't need level, but can use nonlinear electricity to drive leds. From: china electronics wholesale.