Variable off time current-mode floating buck controller - A different approach

Abstract

Switch-mode power supplies have become the premier choice for LED backlighting applications. This paper introduces a new current-mode floating buck controller architecture, used for driving constant current through a string of LEDs. Unlike state-of-the-art controllers, this architecture is based on fixed peak current and variable OFF time as the current control method. An innovative time modulator is added to provide a constant feedback loop response regardless of external components. The proposed controller architecture is designed, implemented in a 0.5µm CMOS process and its performances are validated by simulations and measurements.

Application enhancement for driving large strings of LEDs

“…2). It varies up to a threshold internally generated by the controller [3]. Its maximum value (V PEAK - Fig.…”

“…It has a variable switching frequency, enabling adequate LED driving for a wide range of application parameters (input voltage, inductor value, number of LEDs) [3].…”

“…The proposed converter architecture was implemented using our previously introduced controller fabricated in a 0.5μm 5V CMOS technology [3] [4]. The NDD05N50Z device was used as the SW transistor, the same as in simulations.…”

“…This paper proposes a technique for enhancing the number of series connected LEDs driven by a current-mode floating buck converter with external power switch. Previously, we proposed a converter controller, implemented in a low cost CMOS technology, which adjusts the switching frequency in order to accommodate various values for the input voltage, number of LEDs and inductor [3] [4]. This controller is limited to driving a maximum of 4 series connected LEDs only, at input voltages up to 20V [4].…”