Maxim has introduced an off line LED driver claimed to provides flicker-free dimming from maximum brightness to zero with most leading-edge (triac) and trailing-edge (transistor) dimmers.
Aimed at self-contained LED lamps, MAX16841 can operate from universal inputs (90 to 265Vac) and does not always need electrolytic capacitors.
"Electrolytic capacitors are usually the first component to fail in the driver circuit," said the firm. "If electrolytic capacitors are present from an existing design, the MAX16841 lets the lamp continue to operate even when those capacitors fail."
Maxim's chip attempts to solve the well known LED-dimmer incompatibility problem (see below) by actively shaping the input current.
"The driver ensures flicker-free operation with most electronic transformers and dimmers," claimed the firm. "Dimming efficiency improves because the 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."
This last point is important as most, but not all, LED compatibility schemes involve a power-wasting resistor.
The 16841 can be designed into isolated (fly-back) and non-isolated (buck) configurations.
Constant-frequency control is used, shifting from continuous conduction to discontinuous conduction (DCM to CCM) depending on the input voltage.
Operation is specified over -40 to +125°C.
There is a video
Curiously
According to the Maxim website the device status is 'Active: In Production', however only a two page 'preliminary' data sheet is available.
Has anyone managed to buy these chips?
Has anyone received the full data sheet?
Perhaps under non-disclosure agreement?
Answers please to
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The Problem of Dimming in a Retrofit Application
LEDs are intrinsically dimmable and can be dimmed to zero without significant colour change.
However, the I-V characteristic of an LED+driver is vastly different from an incandescent bulb.
Conventional walls dimmers are not just optimised to work with incandescent loads, they depend on the characteristics of incandescent loads to work at all.
Unless LED bulbs are specifically made to work with dimmers - and there are chips from many manufacturers to allow this (with varying degrees of success) - the lamp-dimmer combination will not work.
"When [simple] 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," said Maxim
The two most common sorts of dimmer are: leading-edge (triac) and trailing-edge (transistor).
Both operate by becoming open circuit to the load through a portion of each mains half cycle.
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," said Maxim.
Maxim has its own solution to dimmer-LED incompatibility - described above.
Many others have been featured in Electronics Weekly including RAIS and various systems using ballast resistors to maintain sufficient current flow.
Few of them dim to zero without diverting significant current into a resistor.
