Drivers ensure flicker-free dimming of tunable LEDs

8th September 2015
Posted By : Nat Bowers
Drivers ensure flicker-free dimming of tunable LEDs

Providing both analogue and PWM dimming control, the AL179x single-, dual-, triple- and quad-channel DC to constant current (DC/CC) LED driver ICs have been unveiled by Diodes Incorporated. When combined with an AC/DC power conversion block and an MCU, these current-ratio-optimised regulators provide a cost-effective, scalable and easy-to-implement solution for smart connected lighting applications that use tunable white and colour LED bulbs.

Operating from a 6.5 to 30V input voltage range, the AL1791/2/3/4 constant-current regulators can drive up to four independent LED channels with a maximum of 500mA per channel or 1.5A total drive current for the AL1792/3/4, or 1A maximum for the AL1791. Each channel can be individually controlled down to 0.125% with 500Hz to 10kHz flicker-free PWM dimming or with analogue dimming down to 1.25%. Using the same pin for both inputs ensures the appropriate analog or PWM dimming response.

Support for deep dimming (to below 1%) is important because the human eye perceives light strength as the square root of the measured light, which is proportional to the dimming current. Similarly, while the human eye only notices flicker below 120Hz, the ability to operate PWM dimming above 1kHz avoids problems with e-Flicker, which is the flicker picked up by cameras such as those found in smart phones that can result in dark bands on still images. The AL179X is capable of high frequency PWM for deep dimming applications: 10kHz at 1.0%, 4kHz at 0.4% and 1kHz at 0.1%.

The AL179x LED drivers all feature an enable pin for low standby power, internal protection for LED string open/short-circuit and under voltage lockout, over-temperature protection with thermal shutdown and auto-recovery and full fault reporting as well as LED power-good reporting. An integrated low-side current sink topology allows for either lower cost common-anode LED connections or different anode voltages for improved energy-efficiency. All devices operate over an ambient temperature range of -40 to +125°C and are packaged in the same 14-pin UDFN-4030 package, which allows for easy scalability of LED driver design in smart, connected-lighting applications.

The single-channel AL1791AFE-13 is available from $0.64 each in 1,000 unit quantities. The AL1794EV1 evaluation board is available on request.


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