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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.

The design of an RF‐power amplifier using the distributed network synthesis in order to achieve the required performance over an operating frequency range is presented. The transfer function of distributed matching circuits, which are useful for the design of RF‐power amplifiers, is derived using an equal ripple approximation. Element values of the network used to match device models are calculated in terms of minimum insertion losses and ripples for a specified network topology. To verify the performance of synthesized circuits, the results are applied to the design of an RF transistor power amplifier with an appropriate device‐modeling technique. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 207–211, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11171

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