This paper proposes a single-stage light-emitting diode (LED) driver based on an inverted buck topology, using current path control switches. The proposed circuit consists of a control circuit, a bridge diode, and an inverted buck converter with multiple switches connected to the LED segments in parallel. Whereas the typical buck LED driver operates with a fixed LED forward voltage, the proposed driver operates with a variable LED forward voltage, according to the input voltage level. Because of this capability to adjust the LED forward voltage, it can reduce the current ripple and the switching frequency with a small inductance value. In addition, it enables operation with LED lamps of a wide voltage range, while simultaneously achieving small dead-angles. The detailed operation principles are described, and the design considerations for the proposed driver are discussed. The proposed driver circuit and control operation are verified experimentally using a 7 W hardware prototype with four LED segments. The obtained experimental results show that, under a 110 Vrms input voltage, the proposed driver achieves a power factor of 0.94 with a small dead-angle and an efficiency of 94 %.
- Buck power factor collection (PFC)
- Constant off-time control
- Light-emitting diode (LED) driver
- Scalable LED string
PROPOSED CIRCUIT DIAGRAM:
Fig. 1. Proposed single-stage LED driver..
EXPECTED SIMULATION RESULTS:
Fig. 2. Simulation results for the proposed LED driver operated at
110Vrms/60 Hz. (a) Overall waveforms. (b) Switching waveforms at input peak
This paper proposes an offline LED driver based on the inverted buck converter. The proposed driver is configured as a hybrid combination of buck topology and multiple switches, which connect to the several LED segments. The proposed driver can reduce both the switching frequency and the LED current ripple using relatively small inductors, because it can adjust the LED forward voltage according to the input voltage level. In addition, it has small dead-angles and achieves high efficiency values when used with high output voltages. The features and operation principles of the proposed LED driver have been described in detail. The overall schematic was presented, and its control method discussed. A 7 W prototype LED driver was implemented and tested. The obtained experimental results verify the operation and performance levels of the proposed driver. At 110 Vrms, it exhibits simultaneously a high efficiency (94 %) and a high PF value (0.94).
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