Chung-Yi Lin

A High-Efficiency Dimmable LED Driver for Low-Power Lighting Applications

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 single-ended 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.

A High-Efficiency AC-to-DC Adaptor With a Low Standby Power Consumption

A two-stage burst mode control scheme for an AC-to-DC adaptor is proposed in this paper. An upper limit for the output voltage is set to turn off both AC/DC and DC/DC controllers at no load. The burst-mode operations of the DC/DC and the AC/DC converters are in turn enabled when reaching the lower limit of the output voltage. Load analysis at standby mode is performed. A 50-mW no-load power loss is observed on an 80 W/12 V prototype adaptor.

Phase-Shifted Full-Bridge Series-Resonant DC-DC Converters for Wide Load Variations

This paper presents the design of a phase-shifted full-bridge series resonant converter (PS-FB SRC). The proposed FB SRC features a novel two-mode operation. It is operated in series resonant mode at normal loads. The switching frequency is varied to regulate the output voltage. The fixed-frequency phase-shifted pulse width modulation, on the other hand, is used to adjust the effective duty cycle and regulate the output voltage at light loads. The proposed converter exhibits high conversion efficiency for wide-range load conditions. The relationships among the voltage gain, the switching frequency, and the effective duty cycle are discussed and analyzed. Finally, a 48-V/42-A prototype is implemented. Experiments are conducted to verify the theoretical analysis.

A Single-Stage Soft-Switching Flyback Converter for Power-Factor-Correction Applications

This letter presents a single-stage soft-switching Flyback converter for power-factor-correction (PFC) applications. High power factor and high conversion efficiency can be achieved by a simple single-stage circuit with soft-switching features. The operation principles and design criteria for the studied PFC converter are analyzed and discussed. A laboratory prototype is also built and tested. Finally, the experimental waveforms for this prototype circuit are shown to verify the feasibility of the proposed scheme.

Analysis and Design of a Push–Pull Quasi-Resonant Boost Power Factor Corrector

This paper proposes a novel power-factor corrector (PFC), which is mainly composed of two-phase transition-mode (TM) boost-type power-factor correctors (PFCs) and a coupled inductor. By integrating two boost inductors into one magnetic core, not only the circuit volume is reduced, but also the operating frequency of the core is double of the switching frequency. Comparing with single-phase TM boost PFC, both the input and output current ripples of the proposed PFC can be reduced if the equivalent inductance of the coupled inductor equals the inductance of single-phase TM boost PFC. Therefore, both the power-factor value and the power density are increased. The proposed topology is capable of sharing the input current and output current equally. A cut-in-half duty cycle can reduce the conduction losses of the switches and both the turns and diameters of the inductor windings. The advantages of a TM boost PFC, such as quasi-resonant (QR) valley switching on the switch and zero-current switching (ZCS) of the output diode, are maintained to improve the overall conversion efficiency. Detailed analysis and design procedures of the proposed topology are given. Simulations and experiments are conducted on a prototype with a universal line voltage, a 380-V output dc voltage and a 200-W output power to verify its feasibility.

Improved control-to-output characteristics of a PWM buck-boost converter

An 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. Copyright

Analysis and design of an active-clamping zero-voltage-switching isolated inverse-SEPIC converter

This paper presents an active-clamping zero-voltage-switching (ZVS) isolated inverse-SEPIC converter. The high voltage spikes when turning off the switches are eliminated. The energies stored in the parasitic elements can be recycled to achieve the ZVS of switches. Therefore, the conversion efficiency increases substantially, yet with a reduced circuit cost. Detailed analysis and design of the proposed topology are described. Experimental results are recorded for a prototype converter with a DC input voltage ranging from 130 to 180 V, an output voltage of 12 V and a rated output power of 120 W, operating at a switching frequency of 65 kHz. The average active-mode efficiency is above 88%. Copyright

Analysis and design of a half-bridge LLC series resonant converter employing two transformers

This paper presents a two-transformer LLC series resonant converter (SRC), which is derived from incorporating two identical converters. The proposed converter allows a low-profile power supply design for liquid crystal display (LCD) TVs and servers. The presented converter can equally share the total load current between two transformers and the output rectifier modules. Therefore, the heat problem can be effectively relieved. The steady-state analysis and design of this new two-transformer LLC SRC are described. The experimental results are recorded for a prototype converter with an output voltage of 12thinspaceV, an output power of 300 W, and a resonant frequency of 74 kHz. Copyright

Analysis and design of a two-transformer active-clamping forward converter with parallel-connected current doubler rectifiers

A new two-transformer active-clamping forward converter with parallel-connected current doubler rectifiers (CDRs) is proposed in this paper. The presented DC–DC converter is mainly composed of two active-clamping forward converters with secondary CDRs. Only two switches are required and each one is the auxiliary switch for the other. The circuit complexity and cost are thus reduced. The leakage inductance of the transformer or an additional resonant inductance is employed to achieve zero-voltage-switching (ZVS) during the dead times. Two CDRs at the secondary side are connected in parallel to reduce the current stresses of the secondary windings and the ripple current at the output side. Accordingly, the smaller output chokes and capacitors decrease the converter volume and increase the power density. Detailed analysis and design of the presented two-transformer active-clamping forward converter are described. Experimental results are recorded for a prototype converter with a DC input voltage of 130−−180V, an output voltage of 5 V and an output current of 40 A, operating at a switching frequency of 100 kHz. Copyright

Analysis and design of a push–pull DCM boost power factor corrector

A novel power factor corrector (PFC) composed of two-phase discontinuous conduction mode (DCM) boost PFCs and a coupled inductor is proposed in this paper. By coupling the two-phase boost inductors into the same magnetic core, both the circuit volume and the input ripple current are reduced. Therefore, the power factor (PF) value and the power density are improved. In addition, the output capacitor size can be smaller. The proposed topology distributes the input current and output current equally for the two phase modules. A cut-in-half duty cycle can decrease the conduction losses of the switches, and both the turns and diameters of the inductor windings, which help more to the reduction of the circuit volume. The advantages of a DCM boost PFC, such as natural zero-current-switching (ZCS) of the output diode, a natural PFC function, and the simplified EMI filter design, are maintained. Detailed analysis and design of the proposed topology, and the experimental results on a prototype with a 380-V output voltage and a 200-W output power are provided.