120VAC offline LED driver board ADM00766 and LED load board ADM00767 main features (Figure)

Microchip's CL88020 is an off-line LED driver with an input voltage of 120VAC and 8.5W of LED power. The device includes the CL88020 LED driver, six resistors and a bridge rectifier. It has programmable overtemperature protection, allowing THD to be thick and optional to reduce light load output. Ripple, using only one external ceramic storage capacitor, TRIAC dimming compatible, mainly used in LED lights and LED lighting fixtures. This article describes the main features of the CL88020, block diagrams and typical application circuits, as well as 120VAC offline LED driver board ADM00766 and LED load board ADM00767 main features, circuit diagrams, bill of materials and PCB design drawings.

The CL88020 LED Driver Integrated Circuit (IC) is anoff-line sequenTIal linear LED driver designed to provide 8.5W of LED power from a 120 VAC nominal inputvoltage.

CL88020 is designed to drive a long string of inexpensive, low-current LEDs directly from the AC mains. Abasic driver circuit consists of Microchip Technology Inc.'s CL88020 LED driver IC, six resistors and a bridgerecTIfier. Two to four addiTIonal components are opTIonalfor various Level of transient protection, also with a low-cost NTC to assure remote overtemperature protection (OTP). No capacitors, EMI filters, or power factorcorrection circuits are needed unless the corresponding modified light output ripple feature is desired.

A string of series/parallel LEDs is tapped at four locations. Four linear current regulators sink current at eachtap through a single control point and are sequentiallyturned on and off. High efficiency is achieved by shuttingoff upstream regulators when downstream regulatorsachieve regulation. Input current easier than trying to control multiple currentpaths, thus tracking the input sine wave voltage.

CL88020 uses a self-commutation techniqueusing only the tap currents themselves; this techniqueinherently provides smooth transitions from one regulator to the next, without relying on tap voltages or therectified AC to coordinate the transitions.

Key features of CL88020:

• Optimized for 120 VAC Nominal Input Voltage
- 120VAC ± 15% input voltage
• Targeted for 8.5W Output Power
• Programmable Overtemperature Protection
- Provides Gradual Reduction in Light Outputwith Increasing Temperature
• Active Line Regulation
- Provides Fairly Constant Output Power overVariations in AC Line Voltage
- Typical Line Regulation of –12% to +0%
• Four Taps with Two Current Set Resistors
- Allows Optimization of THD
• Optional Reduced Light Output Ripple
- Provides Continuous Power to the LED
- Eliminates Strobing
- Uses an External Ceramic Storage Capacitor
• TRIAC Dimmer Compatible
• Available in a Thermally Enhanced 8-Lead SOICPackage with Heat Slug
- Larger Creepage Distances between HighVoltage and Low Voltage Pins