The active clamp flyback (ACF) converter has been widely adopted because of the feature of isolation, soft-switching, and high conversion efficiency. On the other hand, due to the characteristic of the circuit cost reduction and the fast control response, the primary-side regulation (PSR) has become a popular control method for isolated power converters. However, high precision PSR strategies for ACF converters are not exposed. Therefore, the aim of this article is to propose a high precision PSR strategy for the ACF converter. Relations between the primary-side current and the secondary-side current are analyzed and derived. Both of the continuous conduction mode operation and the discontinuous conduction mode operation will be considered. The output voltage control mode or the output current control mode can be selected via the proposed strategy. In addition, a secondary-side losses compensation (SSLC) strategy is developed to deal with the non-ideal circuit characteristics as well as to enhance the control accuracy. Operational principles and thorough mathematical derivations will also be revealed. Finally, both simulation and experimental results obtained from a 100 W prototype circuit demonstrate the performance and feasibility of the proposed PSR and SSLC strategy. Validations show that the control accuracy of the output voltage and the output current are 98.54% and 98.42%, respectively.

An Active Clamp Flyback Converter With High Precision Primary-Side Regulation Strategy

The active clamp flyback (ACF) converter has been widely adopted because of the feature of isolation, soft-switching, and high conversion efficiency. On the other hand, due to the characteristic of the circuit cost reduction and the fast control response, the primary-side regulation (PSR) has become a popular control method for isolated power converters. However, high precision PSR strategies for ACF converters are not exposed. Therefore, the aim of this article is to propose a high precision PSR strategy for the ACF converter. Relations between the primary-side current and the secondary-side current are analyzed and derived. Both of the continuous conduction mode operation and the discontinuous conduction mode operation will be considered. The output voltage control mode or the output current control mode can be selected via the proposed strategy. In addition, a secondary-side losses compensation (SSLC) strategy is developed to deal with the non-ideal circuit characteristics as well as to enhance the control accuracy. Operational principles and thorough mathematical derivations will also be revealed. Finally, both simulation and experimental results obtained from a 100 W prototype circuit demonstrate the performance and feasibility of the proposed PSR and SSLC strategy. Validations show that the control accuracy of the output voltage and the output current are 98.54% and 98.42%, respectively. 

The Renewable energy system, electric vehicle, and telecommunication applications require relatively stable power converters with a high gain and enhanced noise immunity A study of three different types of current-mode controllers for high-gain ultra-lift Luo-converter (ULC) is discussed in this paper The stability of a constant frequency peak current-mode controller (PCM), an average current-mode controller (ACM) and a variable frequency hysteresis current-mode controller (HCM) are analyzed based on small-signal characteristics Using mathematical modeling of the controllers, the closed-loop transfer functions such as control voltage to output voltage, current loop gain, inductor current to control voltage, and audio susceptibility are obtained These transfer functions along with MATLAB simulation results for PCM, ACM and HCM controllers are compared Then, the component losses of the ULC converter using PCM, ACM and HCM controllers are calculated and an efficiency comparison of different control techniques is done Investigations of the voltage and current stresses of the switch and diodes are also carried out Finally, a prototype is fabricated to validate the performance of the converter

Investigation of ultra-lift Luo-converter with peak, average and hysteresis current-mode control

In this paper, a feedback compensator (FBC) and a Feedforward compensator (FFC) are proposed to construct a novel compensated peak current mode control pulse width modulation (CPC-PWM) for primary-side controlled flyback converters. Using the proposed FBC, the PWM duty cycle of an abnormal operating flyback converter would be descended to limit the output current for reducing power dissipation. Using the proposed FFC, the effect of delay time would be descended to reduce the over-flow current for increasing the current accuracy. In this paper, the operating principle and mathematical model are described and analyzed. Then, the component values are well designed to satisfy the electrical specifications. Finally, a prototype is designed and realized to access system performance. The experimental results show that the proposed CPC-PWM can validate in a wide input voltage range and output short conditions, which also has good current accuracy and reduces power dissipation by about 68%.

A Compensated Peak Current Mode Control PWM for Primary-Side Controlled Flyback Converters

For small size, low cost, and wide power range, the constant current (CC) control scheme suitable for both discontinuous conduction mode and continuous conduction mode (CCM) is prevalent in low and medium power applications. However long and short periods (LSP) emerge due to the inner control relationship of conventional flyback converter especially in CCM. An adaptive over current protection (OCP) control scheme is adopted to eliminate LSP. A threshold regulator and a calibrated protector are used to correct the OCP threshold dynamically in the proposed OCP circuit. To verify the feasibility and performance, the proposed scheme has been implemented in $0.18~\mu \text{m}$ BCD process. The experimental results show that the LSP is eliminated and deviation of the CC is within ±1.04% under different input and load conditions.

An Elimination Scheme of Long and Short Periods for Flyback Converter

Primary-side flyback converter (PSR) is widely used among small and medium power applications for its simplicity and cost effectiveness. However, it is hard to measure the current of secondary side due to the special structure characteristic of PSR. Conventionally, a peak current measurement strategy is adopted to measure the current of primary inductor. However, the sampling method is just for one conduction mode and is affected by the propagation delay between the control signal and actual turn- off instant of mosfet . Thus, a compensation circuit is needed to improve the accuracy, which leads to a large area and cost of the controller. In this work, a kind of average inductor current measure and control strategy for multimode is introduced. The average inductor current measurement strategy is based on the Miller stage to recognize the state of the mosfet, which eliminates the error caused by the mosfet . The average current of primary inductor is obtained and there is no need to estimate the rising slope and the peak value of the inductor current. To verify the feasibility of the proposed method, a controller for charging application is fabricated integrated with the proposed method. Hardware experimental results show that the control system can properly operate in multimode. The accuracy of constant output current is ±1% and the line regulation of the system is 1.6% under the input line voltage ranges from 85 to 265 Vac.

Qiang Wu

Papers

Average Inductor Current Measure and Control Strategy for Multimode Primary-Side Flyback Converters