Abstract-This paper presents a dimmable light-emitting diode (LED) driver with adaptive feedback control for low-power lighting applications. An improved pulsewidth modulation dimming technique is studied for regulating the LED current and brightness. Under universal input voltage operation, high efficiency and high power factor can be achieved by a coupled inductor singleended primary inductance converter power factor correction (PFC) converter with a simple commercial transition-mode PFC controller. The operation principles and design considerations of the studied LED driver are analyzed and discussed. A laboratory prototype is also designed and tested to verify the feasibility.Index Terms-Coupled inductor single-ended primary inductance converter power factor correction (SEPIC PFC), dimmable light-emitting diode (LED) driver, universal input voltage.
SUMMARYAn indirect control variable for improving the control-to-output characteristics of a Pulse Width Modulation (PWM) buck-boost converter is introduced in this letter. The voltage gain and the small-signal model of the buck-boost converter are reviewed. The actual voltage command at one input of the PWM comparator is from the proposed indirect control variable and the peak value of the high-frequency PWM carrier. The resulted voltage gain function appears proportional to this indirect control command. Also the dependence of the DC gain of the control-to-output transfer function on the duty cycle is eliminated. Experimental results conform well to the theoretical analysis.
SUMMARYA new method is proposed in this paper to distribute the steady-state output voltage errors in a two-output forward converter. The cross regulation between the two output voltages are described in terms of the circuit parameters. An objective function is formed for each of the two outputs to track its reference within the specified error. The legitimate duty cycle range is located through the transfer characteristics between the duty cycle and the load currents. The weighting feedback gains of the two output voltages can be determined by the presented control scheme which optimizes the objective function. The proposed method is suitable for a two-output system without a dominant load. Experiments on a prototype are conducted to show that there exist a duty cycle range and a set of weighted feedback gains minimizing the defined objective function.
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