A novel on-chip step-dimmer for low cost AC-powered HV-LED driver

Abstract

This letter proposes a novel on-chip step-dimmer using an analog dimming method for a high PF AC-powered LED driver. The full AC LED driver can achieve a very high PF and a low THD by using a self-adaptive power processing circuit while delivering a best-in-class dimming performance with the proposed step-dimmer. Under the control of the dimming signal, the dimming voltage is step-adjusted from 1.0 V to 2.5 V, the average LED current can be changed from 40% to 100% of the nominal LED current value. To verify the feasibility of the proposed scheme, an 8-string 4.4 W AC-powered LED driver with the proposed step-dimmer was designed and simulated using a 0.35 um-700 V BCD Magnachip process. The gained results verify that the proposed step-dimmer can maintain a high performance of the AC LED driver under different dimming modes with a PF and a THD around 0.998 and 6%, respectively.

Line voltage compensation technology for AC-direct multiple-string LED drivers

“…The experimental results show that the output luminance variation is less than 2.0% (1.5%) under 110 V/AC (220 V/AC) AE15% conditions. The proposed technology can also be implemented in other soft self-commutating LED driver topologies, including the structures described in [7], [9] and [10].…”

“…The LED driver described in [10] proposed a variable current level, but only for dimming functions. Unlike the switched mode power supply (SMPS) solutions designed for universal AC input [11,12], one of the major flaws for the AC-direct multiple-string LED driver is the luminance variation due to the AC-mains voltage tolerance.…”

A high power factor LED driver with dual sampling loop feedback control

“…Furthermore, a dimming function has notable benefits such as a comfortable sight and energy saving. The conventional architectural dimming system is based on analog [26] or TRIAC dimmer [27,28] to control current amplitude for regulating lighting brightness. However, LED has fast ignition, so the industry typically uses the PWM dimming [29][30][31][32].…”