This paper integrates a novel primary-side regulation (PSR) scheme with a single-stage high-power-factor (PF) ac-dc light-emitting-diode (LED) driving circuit. The driving circuit is based on the combination of a buck-boost PF corrector and a flyback converter. The component amount, cost, and size can be significantly reduced by replacing the secondary-side regulation with the PSR. In this way, not only high performance but also low cost and small system size can be achieved. Above 0.97 PF and 82% efficiency are obtained from a 12-W (60 W replaced) LED bulb driver prototype.

A Novel Primary-Side Regulation Scheme for Single-Stage High-Power-Factor AC–DC LED Driving Circuit

This paper presents an approach to efficiency optimization in digitally controlled flyback dc-dc converters over wide ranges of operating conditions. Efficiency is characterized and optimized based on power loss modeling and multivariable nonlinear constrained optimization over power-stage and controller parameters. A valley switching technique is adopted to reduce MOSFET turn-on switching loss in discontinuous conduction mode. An optimization procedure is formulated to minimize power loss weighted over a range of operating points, under a cost constraint. A lookup table-based digital controller is applied to achieve on-line efficiency optimization by programming switching frequencies and operating modes based on the efficiency optimization processes. The proposed on-line efficiency optimization approach is verified by experimental results on a low cost 65 W flyback dc-dc prototype.

Efficiency Optimization in Digitally Controlled Flyback DC–DC Converters Over Wide Ranges of Operating Conditions

This paper proposes a primary-side control scheme for low-power light-emitting diode (LED) driver with Flyback topology. With average primary-side current signal and transformer auxiliary winding voltage signal, the output current can be derived and regulated precisely by the proposed control scheme without any isolated feedback circuit. Furthermore, the proposed primary-side control scheme can be implemented with power factor correction control to achieve high input power factor, which is usually required for LED drivers. Since the triode for alternating current (TRIAC) dimming is very popular in practical application, it is preferred that the LED driver can also be compatible with TRIAC dimming. With the proposed control scheme, the input characteristic of the LED driver is resistive like an incandescent bulb. No extra dummy load is needed to provide the TRIAC holding current. Both the output current signal and TRIAC dimming signal can be obtained at the primary side, the TRIAC dimming function can be easily implemented and linear dimming characteristic can be achieved. Detailed operation principles and design considerations of the proposed control scheme are presented in the paper. The experimental results from a 15-W prototype verify the theoretical analysis.

A Primary-Side Control Scheme for High-Power-Factor LED Driver With TRIAC Dimming Capability

A primary-side controlled method is commonly used in flyback LED driver to regulate output current by employing an auxiliary winding. However, owing to intrinsic propagation delay in real-world circuits, a primary-side controlled flyback converter experiences a worse line regulation. This paper proposes a smart output current estimation scheme to improve line regulation for constant on-time control, and it can be compatible with the current flyback topology. A 9.5-W prototype of the proposed flyback LED driver has been fabricated in Nuvoton Technology Corporation 0.6-μm 5-V/40-V CMOS process. The maximum switching frequency is set to around 100 kHz with universal-line input, single-stage power factor correction for LED lighting applications. Experimental results prove that the proposed scheme can improve the line regulation within 1.5% and the power efficiency can be up to 89.7%.

An Adaptive Output Current Estimation Circuit for a Primary-Side Controlled LED Driver

Primary-side sensing (PSS) technique can be used for output voltage or current regulation by employing an auxiliary winding for the sensing of the output voltage without using an additional opto-coupler for output feedback isolation. However, the sensed voltage may be corrupted by switching noises due to leakage inductance, winding resistance, uncertainty of winding parameters, and nonlinearity of the magnetic core, therefore, the sensed voltage can only achieve limited accuracy. This paper makes an error analysis of the PSS technique due to the leakage inductance and other key parameters when applying to flyback converters. Computer simulation has been carried out to verify the proposed error analysis method. The developed error analysis method can be used to improve the design of the flyback transformer and PSS algorithm for the development of more advanced digital primary-side controller in applications to flyback converters.

https://ir.nctu.edu.tw:443/bitstream/11536/17615/1/000277660000016.pdf

Primary-side sensing error analysis for flyback converters

Voltage feedback in flyback converters is typically done with the assistance of opto-couplers, to preserve electrical isolation. However the output voltage also exists (in part) across the primary side switch when in its off state. This paper investigates the extraction of the output voltage within one switching cycle. Good results are obtained from a flyback converter with a novel control circuit using cycle by cycle control. The converter works in both continuous and discontinuous mode of operation.

P. Meaney

Papers

Primary side control circuit of a flyback converter