SUMMARYHere, we propose a single-stage alternating current/direct current electrolytic capacitor-less light-emitting diode (LED) driver, which applies interleaving flyback topology to reduce the peak-to-average ratio of LED driving current. With this approach, the peak current through LEDs is reduced, so the lifetime requirement of LEDs can be satisfied for an electrolytic capacitor-less LED driver. A new transformer with two interleaving auxiliary windings is applied to this driver. Based on this approach, compared with other electrolytic capacitor-less LED drivers, an important advantage of this driver is that it can be easily created, without additional control circuits. We will explain the operation principle and control strategy of the proposed driver in detail and will use experimental results taken from a 24-V 350-mA prototype to demonstrate its performance.
In order to improve the light-load efficiency of active clamp forward converter with synchronous rectifier (SR), power loss analysis of the converter operating in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) are presented in this study. The light-load efficiency of normal ACF converter with SR is low because the output inductor current can go negative when operating in CCM. Considering the fixed frequency control only, to shift the converter's operating mode from CCM to DCM at a critical point of output current at light-load is a solution for efficiency improvement. Based on the CCM and DCM power dissipation models proposed in this study, the power loss characteristics of the converter are analysed, and the critical shift point of output current can be derived, which has also been verified by an experimental prototype.
This paper presents a comprehensive theoretical analysis and an accurate calculation method of the dead-time required to achieve zero-voltage-switching (ZVS) in a battery charger with the phase-shifted full-bridge (PSFB) topology. Compared to previous studies, this is the first time that the effects of nonlinear output filter inductance, varied Miller Plateau length, and blocking capacitors have been considered. It has been found that the output filter inductance and the Miller Plateau have a significant influence on the dead-time for ZVS when the load current varies a lot in battery charger applications. In addition, the blocking capacitor, which is widely used to prevent saturation, reduces the circulating current and consequently affects the setting of the dead-time. In consideration of these effects, accurate analytical equations of the dead-time range for ZVS are deduced. Experimental results from a 1.5kW PSFB battery charger prototype shows that, with the proposed analysis, an optimal dead-time can be selected to meet the specific requirements of a system while achieving ZVS over wide load range.
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