MAX31840 is an LED driver IC for dimmable 12V MR16, as well as AR111 and other 12V lighting applications. This next-generation MR16 LED driver integrates a number of value-added functions: deep dimming, bleeder control, constant brightness control, and a boost FET; while significantly improving electronic transformer compatibility with standard trailing-edge dimmers.
The driver incorporates a proprietary circuit that enables deep dimming down to ~1%; an improvement over others that only dim down to 10% or 20%. An integrated bleeder and constant brightness controller enables the MAX31840 to operate flicker-free, with a broad range of electronic transformers. An optimized compensation circuit and boost FET are integrated to further reduce BOM and board space. The MAX31840 commes in an 8-pin, 3 x 3 mm TDFN enhanced power package and is rated over the -40°C to +125°C operating temperature range.
Maxim’s data sheet enlarges on the dimming characteristic; Controlled by the same dimmer, a Halogen bulb appears to be more dim-able compared with a LED replacement. The brightness of a Halogen bulb is proportional to the cube of the average voltage across its inputs. For an LED replacement, the brightness is linearly proportional to the average voltage across it. The deep dimming circuit adjusts the LED-on duration accordingly and at the limit cuts down the LED-On duration to a minimum at an input phase of about 15%. The deep dimming profile is more gradual at both low and high duties, as seen in the graph below. The MAX31840 controls the boost regulator and bleeder to maintain continuous input current, while lowering the power delivered to the LED’s, in order to achieve this dimming profile.