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Dimmable LED Light Bulbs

Nearly all dimmer commonly mounted in the wall or for desk lamp. The triac dimmer can work perfectly with the incandescent light bulb, but not LED lamp or CFL lamp. Triac dimmer cannot drive LED directly, since LED is not pure resistive load. It needs a LED driver to drive LED. And most of LED driver cannot accept Triac output to adjust LED brightness. LM3445 is a chip designed for Triac application in the market. With using LM3445, we can dim the LED with triac dimmer, and use back the traditional architecture in the luminophor.

The LM3445 is an adaptive constant off-time AC/DC buck (step-down) constant current controller designed to be compatible with triac dimmers. The LM3445 provides a constant current for illuminating high power LEDs and includes a triac dim decoder. The dim decoder allows wide range LED dimming using standard triac dimmers. The high frequency capable architecture allows the use of small external passive components. The LM3445 includes a bleeder circuit to ensure proper triac operation by allowing current flow while the line voltage is low to enable proper firing of the triac. A passive PFC circuit ensures good power factor by drawing current directly from the line for most of the cycle, and provides a constant positive voltage to the buck regulator. Additional features include thermal shutdown, current limit and VCC under-voltage lockout.

• Triac dim decoder circuit for LED dimming
• Application voltage range 80VAC – 270VAC
• Capable of controlling LED currents greater than 1A
• Adjustable switching frequency
• Low quiescent current
• Adaptive programmable off-time allows for constant ripple current
• Thermal shutdown
• No 120Hz flicker
• Low profile 10 pin MSOP Package
• Patent pending drive architecture

Applications
• Retro Fit Triac Dimming
• Solid State Lighting
• Industrial and Commercial Lighting
• Residential Lighting

Since LM3445 is the driver controller, which means that the external switch FET is required. So the driving capability is depends on the selection of external MOSFETs. So it can handle high current mutiple die LED.

LM3445 is not able to drive incandescent lamp, bceause incandescent lamp has different characteristic from WLED. The LM3445 provides a constant current for illuminating high power LEDs and includes a "Triac Dim Decoder". The dim decoder allows wide range LED dimming using standard triac dimmers. The voltage input for LM3445 is not important, But the AC Frequency has two kinds, It is 50Hz or 60Hz.

PWM dimming bulb can not be used in TRIAC dimmer fixture. But the LED bulb with LM3445 can be used in TRIAC dimmer fixture.

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