Design of high performance led driver based on SEPIC topology

Abstract

LEDs are current driven devices. So it is essential to maintain the stability of LED current. Variation of temperature may cause of instabilities and bifurcations in the LED driver. Driving LEDs from an offline power source faces design challenges like it has to maintain low harmonics in input current, to achieve high power factor, high efficiency and to maintain constant LED current and to ensure long lifetime. This work proposes the technique of harmonics reduction by using parametric optimization of Single Ended Primary Inductor Converter (SEPIC) based LED driver. Without optimization of SEPIC parameters input energy will not be properly transferred to the load and this un-transferred energy will be transmitted to the source. Consequently, the quality of input current will be hampered i.e. harmonics will contaminate the input current. Focussing this, we proposed the design of a non-isolated integrated-stage single-switch constant current LED driver operating in Discontinuous Conduction Mode (DCM) in SEPIC incorporating the design of control circuit with soft start mechanism. This LED driver has achieved a good efficiency (90.6%) and high-power factor (0.98) with reduced harmonics (3.35%). System stability has been determined and simulation studies are performed to confirm the validity of the LED driver circuit. A laboratory prototype is built to verify the functionality and performance of the proposed LED driver. There are also some design challenges for a multicolor LED driver like precise control of color consistency i.e. to maintain Corelated Color Temperature (CCT) and luminous intensity. A bicolor blended shade white LED system is formed by using warm color LED source of CCT 1000K and cool color LED source of CCT 6500K. The overall CCT is the blended CCT of the two LED sources. This work also approaches the method of nonlinear optimization of LED currents of both sources for reducing deviation of blended CCT from the target in order to achieve desired CCT from the two LED sources of the multicolor LED driver. These optimized LED currents in the two strings are maintained by the control circuit of the SEPIC. The obtained deviation of CCT is 43K, precision is above 99.15%, which is not perceived by human eyes. Another design challenge is to drive LEDs to maintain low harmonics in the input current. This work again proposes the harmonic reduction technique by using parametric optimization of SEPIC based bicolor LED driver. The Non-linear Constrained Parametric Optimization Methodology is deployed to refine the SEPIC parameters to have the least value of Total Harmonic Distortion (THD). The power loss analysis has been performed to minimize losses in order to enhance efficiency. Measured THD (4.37%), P.F. (0.96) and efficiency (92.8%) are satisfactory. Over voltage protection mechanism is incorporated in the experimental driving system for safety count. The system stability has been ensured.