C. K. Tse

Color Control System for RGB LED With Application to Light Sources Suffering From Prolonged Aging

This paper presents a unified approach to controlling the white color point of the red/green/blue (RGB) light-emitting diode (LED) existing in all aging states. In contrast to conventional color control systems where the average driving currents of the primary-color LEDs can become saturated when the LEDs have undergone prolonged aging, which causes the resulting white color point to go out of regulation, the proposed method avoids this problem by adjusting the color set points when a predefined threshold current is reached by one or more of the primary-color LEDs. It is shown that the method can effectively maintain the white color point of RGB LED at the desired value when the primary-color LEDs are subjected to an accelerated aging through repetitive current stress cycles.

Application of duality principle to synthesis of single-stage power-factor-correction voltage regulators

The duality principle is applied to derive new single-stage power-factor-correction (PFC) voltage regulators. This paper begins with an application of duality transformation to conventional discontinuous-conduction-mode buck, buck-boost and boost converters. The resulting dual converters operate in the discontinuous capacitor voltage mode. These new converters provide the same PFC property, but in the dual manner. It is proved that in the practical case of the input being a voltage source, the mandatory insertion of inductance between the voltage input and the ‘dual PFC converter’ does not affect the power-factor-correcting property. A new single-stage PFC regulator is derived by taking the dual of a well-known circuit based on a cascade of conventional boost and buck converters. Analytical design expressions are derived, illustrating the relation between current stress and component values. Experiments are performed to confirm the operation of the circuit and its power-factor-correcting capability. Copyright

Elimination of electrolytic capacitor in LED power supplies by two-phase driving approach

A two-phase driving approach for light-emitting-diode (LED) applications is proposed in this paper. In the approach, two rectangular AC sources are employed so that the output current ripple can be significantly reduced. It leads to the elimination of electrolytic capacitor from the driver circuit. The approach is realised by a dual asymmetrical half-bridge converter with LEDs as the load. Considering the mandatory lighting standard for an AC/DC LED driver, the half-bridges are preceded by a valley-fill circuit for meeting the input power factor (PF) and current harmonic distortion requirements. Unlike other existing interleaved LED drivers that can only obtain low current ripples in certain operating points, the proposed approach can maintain a constant output current at all times even under large duty cycle dynamics due to the use of a valley-fill circuit. To validate the feasibility of the proposed approach, a 13 W prototype is built and tested experimentally.

A SYMBOLIC CIRCUIT MODELING PROGRAM FOR DC/DC POWER CONVERTER CIRCUITS

In this letter a computer-based symbolic circuit modeling program, applicable to any arbitrary PWM dc/dc converter circuit, is presented. From the circuit description, this program automatically ge...