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LED driver for retrofit lamps dims to zero light

LED driver for retrofit lamps dims to zero light

Maxim Integrated Products announces the MAX16841, an offline LED driver that enables flicker-free dimming from maximum light intensity down to zero with leading-edge (triac) and trailing-edge (transistor) dimmers. Constant frequency control optimizes efficiency at both low and high ac line voltages. With a 90 to 265 Vac input range, the MAX16841 is a universal fit for Japanese, Chinese, U.S., and European dimmer models.

It allows easy replacement of incandescent and halogen lamps, thereby eliminating compatibility issues with preinstalled dimmers. The MAX16841 prolongs the life of the LED lamps because it can operate without electrolytic capacitors. Eliminating those capacitors also saves space and cost. This LED driver is suitable for retrofit dimmable LED lamps and universal LED bulbs in industrial, commercial, and residential lighting applications.

A dimmer increases or decreases the amount of power supplied to the lamp, increasing or decreasing the light emitted. Today, the two most common ways to vary the voltage are through leading-edge (triac) and trailing-edge (transistor) dimmers. Both types of dimmers operate by removing a portion of the ac waveform to regulate the amount of power reaching the lamp. As their names suggest, the leading-edge dimmer removes the leading edge of the waveform just after it passes through zero, while the trailing-edge dimmer removes the portion just before it passes through zero. Leading-edge dimmers are suitable for use with resistive or inductive loads, while trailing-edge dimmers are suitable for use with resistive or capacitive loads.

To retrofit traditional lamps easily, LED lamps must be compatible with both leading-edge and trailing-edge dimmers. These dimmers are typically designed for the perfectly resistive loads of traditional halogen and incandescent lamps. LED drivers, however, are nonlinear and not ideally compatible with the purely resistive loads of the dimmers. So, when LED lamps are placed into an existing electrical infrastructure with dimmers, the LED lamps generally flicker, will not dim, and in some cases do not turn on at all.

The MAX16841 solves this dimming problem with a unique approach to control the lamp’s input current. By actively shaping the input current, the driver ensures flicker-free operation with most electronic transformers and dimmers. Now LED lamp designers can reliably create drop-in replacements for halogen and incandescent lighting with dimming down to zero light and without the need for costly infrastructure upgrades.

The MAX16841 can be designed in isolated (flyback) and nonisolated (buck) configurations and is, therefore, suitable both for high-ac line voltages (220 to 230 Vac) and low-ac line voltages (100 to 120 Vac). A constant-frequency control scheme improves efficiency by using the optimal conduction mode (DCM or CCM), depending on the input voltage. Dimming efficiency also improves because the MAX16841’s current-control technique does not require current bleeders for the hold current of the dimmer, because sufficient hold current is already guaranteed by the switching regulator itself.

The MAX16841 can be configured for a universal input (90 to 265 Vac), providing its flicker-free dimming in retrofit applications around the globe. With no need for separate LED drivers to satisfy international voltage requirements, the MAX16841 also reduces inventory and design costs.

The MAX16841 can be designed in without electrolytic capacitors. This extends the lifetime of the LED lamp, because electrolytic capacitors are usually the first component to fail in the driver circuit. If electrolytic capacitors are present from an existing design, the MAX16841 lets the lamp continue to operate even when those capacitors fail. Eliminating electrolytic capacitors also reduces the cost and size of the driver. The MAX16841 is fully specified over the -40° to 125° C temperature range.

For more information, contact Maxim Integrated Products, 120 San Gabriel Dr., Sunnyvale, CA 94086. Phone: (408) 737-7600.


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