With the advent of high-power LEDs , the service life of LEDs and power conversion efficiency have become the main considerations in the design of LED lighting systems. Based on Fairchild Semiconductor FAN100, a high-efficiency, high-stability LED lighting system is designed. The circuit, then analyzes the performance of the circuit, and finally performs experimental simulation. It can be seen from the simulation results that the system is relatively stable in the range of large temperature fluctuations. At present, there are two types of power input systems on the market: one type of front end is an AC power input system plus a back end current control module, such products include freezer light strips, indoor lamps, street lamps, table lamps, MRl6, ARlll, and the like. The other is an AC power direct input system that integrates AC/DC converters and constant current lines. These products include bulb-type LED lamps such as E27 and GU10, PAR lamps, T5 and T8 LED tubes. In this paper, the constant current source is used to drive the diode to emit light. When the current of the LED is reduced, the constant current source circuit collects the changed (decreased) current value. After amplification, it is transmitted to the control circuit. The control circuit inverts the sampled signal and outputs it. The pulse width is increased, and the output pulse having an increased width drives the power tube of the power conversion stage, so that the secondary output voltage is increased, so that the voltage across the series LED is also increased, and thus the current flowing through the LED is also increased. The current of the LED is kept constant. Similarly, if the current of the LED is increased for some reason, the control process is reversed. The constant current source driving method can overcome the inconsistency of the voltage drop of the high power LED tube. And the disadvantage of changing the current and luminous efficiency of the tube due to poor temperature characteristics. 1 hardware circuit 1.1 Introduction to FANl00 FANl00 is a primary-side regulated PWM controller that meets the critical needs of the high brightness (HB) light-emitting diode (LED) market. With built-in proprietary TRUECURRENTTM technology and a rigorous constant voltage (CV) range, the most accurate constant current (CC) control is achieved without the need for a secondary-side feedback circuit. By accurately constant current over a wide voltage range, the same circuit can be used for a different number of strings of LEDs, increasing design flexibility, reducing time to market, and extending the life of HBLEDs. Due to the high level of integration of these PSR PWM controllers, board space can be saved to match the trend of shrinking bulb dimensions. The FANl00 features a proprietary power-saving mode that provides turn-off time modulation to linearly reduce the PWM frequency under light load conditions. In addition, they minimize power consumption (standby power at no load) by reducing secondary-side feedback circuits and components. 1.2 overall circuit Figure 1 Constant current driver overall circuit FANl00 Description: 1 pin is the analog input, current detection, the peak current mode connected to the current sense resistor controls the constant voltage mode, and the current detection signal also provides the CC mode of the output current regulation. 2, 6 feet are the grounding terminal. Pin 3 is the analog output. 4 feet for analog output, voltage compensation. Pin 5 is an analog input, voltage terminal. Pin 7 is the voltage reference. Pin 8 is the drive power output. Working process: Frequency hopping PWM mode of operation, using minimal filtering components for EMI problem methods. The VDD pin (pin 7) is equipped with overvoltage protection and undervoltage lockout, pulse current limiting of the pulse and CC control to ensure overcurrent protection. The gate output is clamped at 15 V to protect the external MOSFET from overvoltage damage, and the internal overtemperature protection function is turned off and overheated when the controller is latched. The startup current is 10μA and the low startup current allows for a startup supply with a high resistance and low startup resistance power supply controller. A 1.5 MΩ, 0.25 W start-up resistor, 10μF/25 V is an AC to DC power adapter with a wide input range (100VAC to 240VAC). The FANl00 built-in provides better temperature compensation for constant temperature regulation in different environments. This internal compensation current is a positive temperature coefficient (PTC) current that compensates for the temperature change of the forward voltage drop diode. This change causes the output voltage temperature to rise. The sensor senses the entire current sense resistor voltage for current mode control and the pulse is used to limit the current by the pulse. The slope compensation built-in improves stability and prevents subharmonic oscillations due to peak current mode control. The FANl00 has a synchronous, active, tilted ramp built into each switching cycle.
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