"Keywords:
Fairchild, fl7730, LED drive, dimming
Fairchild's fl7730 is a highly integrated PWM controller that provides enhanced performance for a single-stage flyback converter with its proprietary truecurrent ™ The topology simplifies the circuit design of LED lighting. The application voltage is 80vac ~ 308vac, the starting current is 20ua, and the working current is 5mA. Frequency hopping has better EMI performance, which is mainly used in LED lighting system. This paper introduces the main characteristics, block diagram, typical application circuit of fl7730 and the reference design circuit diagram of LED Driver with triac dimming 180v-265vac and 90-140vac of fl7730
FL7730MY: Single-Stage Primary-Side-RegulaTIon PWM Controller for PFC and LED Dimmable Driving
This highly integrated PWM controller, FL7730MY, provides several features to enhance the performance of single-stage flyback converters. The proprietary topology, TRUECURRENT ™, enables the simplified circuit design for LED lighTIng applicaTIons.
TRIAC dimming is smoothly managed by dimming brightness control without flicker. By using single-stage topology with primary-side regulaTIon, an LED lighting board can be implemented with few external components and minimized cost. It does not require an input bulk capacitor or feedback circuitry. To implement good power factor and low total harmonic distortion, constant on-time control is utilized with an external capacitor connected to the COMI pin.
Precise constant-current control regulates accurate output current versus changes in input voltage and output voltage. The operating frequency is proportionally changed by the output voltage to guarantee Discontinuous Conduction Mode (DCM) operation with higher efficiency and simpler design. The FL7730MY provides protections such as open-LED, short-LED, and over-temperature protections. Current-limit level is automatically reduced to minimize output current and protect external components in a short-LED condition.
The FL7730MY frequency-hopping function in the oscillator improves EMI performance. The FL7730MY controller is available in an 8-pin SOP package.
Main features of fl7730:
Compatible with Traditional TRIAC Control (No need to change existing lamp infrastructure: wall switch & wire)
Compatible with Non-Dimming Lamp Designs
Cost-Effective Solution without Input Bulk Capacitor and Feedback Circuitry
Power Factor Correction (PFC)
Accurate Constant-Current (CC) Control, Independent Online Voltage, Output Voltage,Magnetizing Inductance Variation
Line Voltage Compensation for CC Control
Linear Frequency Control for Better Efficiency and Simple Design
Open-LED Protection
Short-LED Protection
Cycle-by-Cycle Current Limiting
Over-Temperature Protection with Auto Restart
Low Startup Current: 20 μ A
Low Operating Current: 5mA
Frequency Hopping for Better EMI Performance
SOP-8 Package Available
Application Voltage Range: 80VAC ~ 308VAC
Fl7730 application:
LED Lighting System
2012-2-15 12:53:10 upload
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Figure 1. Fl7730 block diagram
2012-2-15 12:53:10 upload
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Figure 2. Typical application circuit diagram of fl7730
Reference design of triac dimming 8.4w LED Driver with fl7730
A LED has become a promising light source for replacing conventional lighting systems, such as fluorescent and incandescent lights. Especially in the conventional TRIAC dimmer infrastructure, there has been much research into development of an LED bulb compatible with TRIAC dimmers. Because the incandescent light source consumes a hundred watt with short life time, an LED bulb can be the excellent substitute with considerably less power dissipation and longer life.
The biggest recent issue of TRIAC dimmable LED bulb is dimmer compatibility. The conventional TRIAC dimmer was originally designed to handle hundreds of watts induced by incandescent bulbs. An LED bulb consuming less than 20W should interact with those dimmers composed of high-power devices. If the interaction between dimmer and LED bulb is not st abilized, visible flicker is perceptible.
To manage the interaction without flicker, some requirements for dimmer operation need to be considered.
TRIAC dimmer needs latching current at firing and holding current during TRIAC turn-on after firing. If those two currents are not met, TRIAC dimmer misfires and LED light flickers. The TRIAC dimmer blocks input line in the beginning of line cycle, then connects input line and LED bulb after firing. The TRIAC dimmer turns off if latching or holding current flowing through the dimmer is inadequate. The latching and holding currents are different from dimmer models. The typical range of latching and holding currents is around 5 ~ 50mA. Those operating requirement do not cause problems using i ncandescent bulbs due to high power consumption. An LED bulb with less than 20W output power cannot maintain this amount of current over the whole line cycle.
This application note provides a practical guideline of TRIAC dimmable LED bulb board design. Passive and active bleeder design guides detail how to maintain latching and holding current without visible flicker. Active damper design improves efficiency by minimizing the count of external components. The input filter design section covers the effec t of filter components on PF, THD, and EMI.
The following user guide supports the demonstration kit for the FL7730.
Triac dimming LED driver reference design main characteristics:
Compatibl
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