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

This paper presents series capacitor dual inductor switching power convertor that features dual output capability and reduced V DD /2 switching voltage. The dual output capability allows circuit to be configured as DC/DC power converter with two distinct outputs, or a DC/AC power inverter. The output voltage range is limited to V DD /2, and it is therefore suitable for applications with high downscale ratio. The structure is based on a series capacitor topology which features reduced V DD /2 switching voltage for both channels and also reduced V DD /2 maximal ratings of switches and series capacitor. This reduces considerably the active area and dynamic (switching) power losses of the converter. Structure also feautures passive flying capacitor voltage balancing ensured by one reduced auxiliary capacitor.

Series Capacitor Dual-output DC/DC Converter and Power Inverter with Reduced Switching Voltage and Stress on Switching Devices

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. 

This paper proposes a hybrid converter with multiple sources for lithium battery charger applications. Since the output voltage of a lithium battery charger is very low, its charger needs a higher step-down voltage for a utility line source or a step-down voltage for PV arrays. In order to implement the battery charger with utility line and PV arrays sources to simultaneously supply power to battery, a flyback converter is selected for utility line sources, and a buck converter is adopted for PV arrays source. Due to leakage inductor of transformer in flyback converter, an active clamp circuit is introduced into flyback converter to recover the energy stored in leakage inductor. In addition, flyback and buck converters can adopt switch integration techniques to simplify circuit structure. With this approach, the proposed hybrid converter has less components, is lighter weight and has smaller size and higher conversion efficiency. Finally, a prototype of the proposed hybrid converter with output voltage of 5 V~8.4 V and output maximum current of 12 A has been implement to verify its feasibility. It is suitable for the lithium battery charger applications.

/pdf/hybrid-converter-with-multiple-sources-for-lithium-battery-3dogdh1m.pdf

Hybrid Converter with Multiple Sources for Lithium Battery Charger Applications

In this paper, a QR flyback converter using a self-driven active snubber (SDAS) was proposed to solve the problem of voltage surge in the switch of QR flyback converters. In the proposed converter, the SDAS consisting of a clamping capacitor and an active switch can be configured in parallel with the main switch or transformer to reduce the voltage surge in the switch. To confirm the steady-state characteristics of the QR flyback converter to which the proposed SDAS is applied, equivalent circuits for each state were constructed, and the equations and characteristics for each state were determined. A 60 W class small AC–DC adapter was constructed to confirm the effectiveness of the proposed converter and the control circuit method, and the experimental results were analyzed. The size of the experimental AC–DC adapter was 74×29×23 mm, and it had a high power density of 20 W/in3 or more. The experimental circuit was limited to the high power conversion efficiency of up to 91.56%, and the maximum voltage surge in the switch was approximately 450 V. One of the reasons for such high efficiency is the SDAS circuit, which sufficiently reduces the voltage surge of the QR flyback switch, compared with the RCD clamp circuit, and does not consume power in principle.

/pdf/a-high-efficiency-qr-flyback-dc-dc-converter-with-reduced-2g1abnb3.pdf

A High-Efficiency QR Flyback DC–DC Converter with Reduced Switch Voltage Stress Realized by Applying a Self-Driven Active Snubber (SDAS)

Active-clamp flyback converter is now widely used because higher efficiency is obtained with soft-switching technique. However, opto-coupler is always applied in the feedback loop to acquire the output signal. To avoid the non-linearity and temperature drift of the opto-coupler, a constant current digital control method with peak current control is proposed for primary-side regulation active-clamp (PSRAC) flyback in this paper. Considering the charge balance principle, the output current can be calculated and controlled with primary-side control and only one low speed digital to analogy converter (DAC), two comparators and a digital unit are required in discontinuous conduction modulation (DCM) mode. Based on the proposed method, constant output current is realized. The proposed control scheme was verified by a FPGA controlled 2.00-10.00V/2.00A ac-dc PSRAC flyback converter.

A Constant Current Digital Control Method for Primary-Side Regulation Active-Clamp Flyback Converter

In low power applications, primary-side regulation (PSR) flyback converter with discontinuous conduction modulation (DCM) mode is widely used to realize constant output current for its simple structure and low cost. In peak current control method, the output current can be predicted from the primary peak current, the demagnetization time and the switching period. Based on the current prediction, a pulse width modulation (PWM) mode and a pulse frequency modulation (PFM) mode are used. However, as the output current cannot be sampled directly in PSR flyback converter, traditional small-signal modelling method based on the control and output variables cannot be used. And there is no stability analysis for these constant current (CC) controlled PSR flyback converters. In this paper, a discrete matrix analysis method is proposed to analyze the stability of CC controlled PSR flyback converter. An iterative matrix of the control and output variable perturbations is obtained and the stability can be acquired from the eigenvalues. Oscillation occurs in above PWM mode and stable control is realized in PFM mode. An improved PWM mode is thus proposed and analyzed for stable control. The analysis is verified in a PSR flyback converter with 1.92A.

Stability Analysis of Constant Current Controlled Primary-Side Regulation Flyback Converter

Constant current controlled flyback converter is widely used in low power applications for its simple structure and low cost. In order to further improve the output power and the efficiency, active-clamp flyback converter with soft-switching technique is always used. To avoid the nonlinearity and temperature drift of opto-coupler in the feedback circuit, a constant current digital control method is proposed for a primary-side regulation active-clamp (PSRAC) flyback converter in this article. Soft-switching technique is realized in discontinuous conduction modulation mode with a modified active-clamp technique. To compensate the nonlinearity of the secondary diode current with primary-side regulation, a new output current estimation algorithm is put forward based on the charge balance principle. The output current is predicted from primary current and the auxiliary winding voltage, and constant output current control is realized with primary peak current control method. The cost is low as only one low speed digital-to-analog converter, three comparators and a digital controller are required. The proposed control scheme was verified by a field-programmable gate array controlled 5.4–10.8 V/1.80 A PSRAC flyback converter. The output current accuracy is within in 1.2% in different input and output condition and the peak efficiency is improved by 3.6% after active-clamp technique is used.

Due to the increasing resolution, the duty cycle in digital pulsewidth modulation (DPWM) is affected by the variation of external clock frequency or temperature, and the time error becomes larger and larger, even reaches a few nanoseconds. The increment of the duty cycle will affect the regulation performance of the converter and the output of DPWM. In this article, a delay-line DPWM architecture with a compensation module and a delay-adjustable unit based on delay-locked loop is proposed. The delay-adjustable unit is realized by using a multiplexer and some delay paths with different delay times, which effectively reduces the influence of temperature or the frequency changes from the input clock. Furthermore, a time compensation method is used to reduce the error generated by the critical path delays. A 10-bit DPWM with 781-kHz switching frequency is achieved on A-7 (xc7a100tfgg484) Xilinx FPGA, and the time error of the architecture decreases to around 500 ps. The duty cycle range is from 1.63% to 98.44%.

A Delay-Line DPWM Architecture With Compensation Module and Delay-Adjustable Unit Based on DLL

A digital single period control method for fast response and low cross regulation of the single-inductor dual-output (SIDO) DC-DC buck converter is introduced in this paper. The digital control method consists of two different algorithms for different scenarios, the zero current control algorithm is put forward to deal with the cross regulation, and the control sequence change method algorithm is adopted to improve the dynamic response of the SIDO buck converter. The experimental results demonstrate that the overall performance of the SIDO buck converter operating at the CCM mode can be improved effectively via the digital single period control method.

Daying Sun

Papers

A Constant Current Digital Control Method for Primary-Side Regulation Active-Clamp Flyback Converter

Stability Analysis of Constant Current Controlled Primary-Side Regulation Flyback Converter

A Constant Current Digital Control Method for Primary-Side Regulation Active-Clamp Flyback Converter

A Delay-Line DPWM Architecture With Compensation Module and Delay-Adjustable Unit Based on DLL

A Digital Single Period Control Method for Single-Inductor Dual-Output DC-DC buck converter