Offline LED Driver for Retrofit Lamps Dims to Zero Light Intensity Without Flicker

The Problem of Dimming in a Retrofit Application
A dimmer increases or decreases the amount of power supplied to the lamp, thus 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 that reaches 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 seamlessly, 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 very nonlinear and not ideally compatible with the purely resistive loads of the dimmers. As a consequence, when LED lamps are inserted into an existing electrical infrastructure with dimmers, the LED lamps generally flicker, do not dim, and in some cases do not turn on at all.

The MAX16841 solves this dimming problem with a unique, proprietary 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 intensity and without the need for costly infrastructural upgrades.


Flexibility Optimizes Efficiency in All Operating Conditions
The MAX16841 can be designed in isolated (flyback) and nonisolated (buck) configurations and is, therefore, ideal both for high-AC line voltages (220VAC to 230VAC) and low-AC line voltages (100VAC to 120VAC). 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, since sufficient hold current is already guaranteed by the switching regulator itself.

Universal Input Expands Applications, Reduces Design Time and Cost
The MAX16841 can be configured for a universal input (90VAC to 265VAC), thus providing its flicker-free dimming in retrofit applications across the globe. With no need for separate LED drivers to satisfy international voltage requirements, the MAX16841 also reduces inventory and design costs.

Extends Lamp Lifetime and Saves Space
The MAX16841 can be designed in without electrolytic capacitors. This extends the lifetime of the LED lamp, since 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 which fits in small form factors.

Additional Details
The MAX16841 is fully specified over the -40 degrees Celsius to +125 degrees Celsius temperature range. It is available in an 8-pin SOIC package. Prices start at $1.35 (1000-up, FOB USA).