lowpowerZONE Products for the week of January 31, 2011

Maxim Integrated Products Says…

MAX16840: LED solution enables drop-in replacements for halogen MR16 lamps
Solution enables the design of LED-based MR16 lamps that are compatible with most electronic transformers and cut-angle dimmers

Maxim Integrated Products introduced the MAX16840, an LED driver that employs a proprietary architecture to ensure flicker-free, dimmable operation with electronic transformers and cut-angle dimmers. Maxim's patent-pending approach enables the design of retrofit LED lamps that can replace halogen MR16s without any changes to the existing electrical infrastructure. This removes an important obstacle to commercial viability, allowing end users to enjoy all the benefits of LED lighting with substantially lower deployment costs.

Designing LED retrofit lamps

To facilitate adoption, LED retrofit lamps must be compatible with electronic transformers and cut-angle dimmers. These transformers and dimmers are designed for the perfectly resistive loads of traditional halogen lamps. LED drivers, however, are very nonlinear and not purely resistive loads. As a consequence, LED lamps flicker, do not dim, and in some cases do not turn on at all when used with the existing electrical infrastructure.

The MAX16840 solves this problem by using a unique, patent-pending approach to control the input current of the lamp. By actively shaping the input current it ensures flicker-free operation with most electronic transformers and dimmers. This enables LED lamp designers to create drop-in replacements for halogen MR16s, thus eliminating the costly infrastructural upgrades required by competitive solutions.

EN-Genius Says…

Before all our houses are wired for dc lighting the “tweenie” stage of conversion from incandescent lighting to LEDs – avoiding the nasty government-mandated environmento-guilty CFLs – is to have some form of conversion products for existing sockets. Most of those are, hopefully, going to come from products that directly take 85 Vac – 250 Vac inputs and provide direct driving to the LEDs, and one of those may have been announced by Diodes Inc. in this last week. This Maxim part takes another but equally welcome approach in offering a conversion path for 12 Vac sourced halogen fixtures, normally in the very familiar MR16 spot format, and for other low-voltage lamps.

The challenge with such an LED driver is allowing the use of not just the 12 Vac input but also allowing for existing dimming equipment to be used: either trailing-edge dimming with electronic transformers or leading-edge dimmers with magnetic transformers. Maxim does this with patent-pending constant-frequency average current shaping to compensate – like a gamma corrector – for the inherently non-linear characteristics of the LED.

The Maxim solution also allows for a design where the input capacitance can be ceramic, eliminating the most-likely-to-fail electrolytic capacitor of other designs. This latter becomes crucially important when you see manufactured fittings from Asia continually built using under-voltage-rated electrolytics to save costs with 80 V devices used in 110 Vac products and 6.3 V devices used in 12 Vac products.

Maxim integrates the switching MOSFET in the MAX16840 (48 V rated with a 200 mΩ Rds(on)) and the design allows for buck, boost and buck-boost topologies. An external npn driver is required to provide a moderate turn-on load for electronic transformers with the driver turned off when the undervoltage lock-out threshold is passed (about 5 V). Overvoltage protection is also provided.

Maxim only let themselves down on this product by the paranoia exhibited by releasing only the front page of the data sheet. This is unacceptable for a $2 billion company in the analog space and suggests an insecurity that is rather unbelievable – and undoubtedly allowed to be fed by senior management.

The ten or so components required for operation of the MAX16840 should allow for the system incorporation in the body of an MR16 fitting quite handily. The part can deliver up to 20 W. This will be a high volume product.

The MAX16840 is in a thermally-enhanced TDFN-10 specified over the -40ºC to +125ºC temperature range with pricing at $2.01 in 1000-piece lots.

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