A weak voltage analog dimming method for high precision light emitting diode (LED) current control with N-Bits analog static offset calibration (N-Bits ASOC), dynamic offset cancellation (DOC) and K-times dimming duty to voltage (KD2V) conversion is presented. The N-Bits ASOC circuit decreases the analog dimming error to V OSMAX /2 N − 1 by pre-calibrating the error amplifier offset. Moreover, through a smart combination of KD2V circuits and DOC amplifier, the KD2V and DOC operational amplifier magnify the dimming reference and LED current sense voltage K-times, respectively, which reduces the residual dimming error K-times without any modification to the LED current sampling resistor. Based on the 0.18µm 5V/40V Bipolar-CMOS-DMOS (BCD) process, experimental results for a cell phone backlighting driver show that the analog dimming I LED error reduces to 30µA at maximum 200mV LED current feedback voltage. This deviation mostly keeps constant through a dimming duty range of 0.5% to 100% and V IN range of 2.7V to 5.5V. Furthermore, a 200-sample measurement data suggests that this method is effective even when dimming duty is smaller than 0.5% for mass production.INDEX TERMS LED analog dimming, pulse width modulation (PWM) dimming, dynamic offset cancellation (DOC), analog static offset calibration (ASOC).
Good teaching effect comes from effective teaching design. In this article, we combined the advanced teaching concept BOPPPS model with Tina virtual simulation software to develop the teaching design. BOPPPS model is an effective and efficient teaching model. It includes six parts such as bridge-in, objective, preassessment, participatory learning, postassessment, and summary. In this article, bridge-in is introduced by practical examples of triode amplifier circuits. Objective includes knowledge objective, ability objective, and value objective. Preassessment is realized by simulating the triode output characteristic. Participatory learning is presented by simulating three kinds of basic amplifier circuits and analyzing simulation results. Besides that, flipping classroom is designed to stimulate students’ learning enthusiasm and innovation ability. Postassessment is completed by asking some questions. Summary is completed by students and supplemented by teachers. In this process, different simulation waveforms are obtained by using the Tina virtual software to simulate the various circuits layer by layer. Practice has shown that the proposed method not only improves students’ ability of analyzing and designing practical circuits, but also stimulates students’ learning enthusiasm. Teaching design ideas become clearer, and the teaching quality is improved.
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