Primary-side Regulation Flyback Research Articles

An Improved Constant Current Control Scheme for Multimode PSR Flyback Converter

For low cost and wide power range, the constant current (CC) control scheme for multimode primary-side regulation (PSR) flyback converter is prevalent in low and medium power applications. Although some multimode CC control schemes have been presented to raise CC accuracy, the current deviation caused by the mode conversion and inherent propagation delay remains unsolved. An improved CC control scheme is adopted to mitigate the influence of propagation delay or mode conversion on CC accuracy, which can be added into an IC controller with no extra pin penalty. The proposed scheme is implemented in 0.18lm 5V/40V BCD process. The experimental results reveal that the deviation of the output current is within 1 0.8% under different input and load conditions.

Digital Voltage Sampling Scheme for Primary-Side Regulation Flyback Converter in CCM and DCM Modes

Primary-side regulation (PSR) flyback topology with discontinuous conduction modulation (DCM) mode has been widely used in low-power application due to its high stability, wide input voltage range, low cost, and low standby power. To improve the output power, continuous conduction modulation (CCM) mode is always introduced. However, in CCM mode, conventional PSR voltage-sampling method cannot realize high precision of output voltage or the voltage sampling method requires complex control of high cost. In this paper, a simple digital voltage sampling scheme with two reference voltages outputted from a digital-to-analog converter (DAC) is put forward to trace the “accurate-point” voltage for DCM and CCM modes. In CCM mode, the sampling voltage error of the “knee-point” voltage can be compensated just by inserting DCM switching cycle to obtain the “accurate-point” voltage. Voltage difference between DCM mode and CCM mode will be eliminated, and high precision is easily realized. The proposed method is verified in a 20V, 65W PSR flyback converter. The sampling method only requires a low speed DAC, three comparators and a digital controller. The output voltage precision is within 0.6% with universal input voltage.

A Constant Current Control Scheme for Primary-Side Controlled Flyback Controller Operating in DCM and CCM

Primary-side regulation (PSR) flyback converters operating in discontinuous conduction mode (DCM) are widely used in low-power applications. In DCM, the peak current control method for PSR flyback is generally adopted to achieve constant current (CC) output. However, there are few effective schemes suitable for DCM and continuous conduction mode (CCM) operation of PSR flyback converters due to the difficulty in estimating the output information correctly, especially in the case of analog circuit control. In this article, a control scheme based on midpoint sampling method is proposed to achieve a high-precision CC control, which operates seamlessly as the operating mode switched between DCM and CCM. In order to verify the feasibility and performance of the proposed control, a control IC with the proposed CC control scheme has been implemented in 0.18 μm 5 V/40 V BCD process. The experimental results show that the deviation of the output current is within ±1.93% under different input and load conditions.

Stability Analysis of Constant Current-Controlled Primary-Side Regulation 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, demagnetization time, and switching period. Based on the current prediction, a pulsewidth 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 modeling method based on the control and output variables cannot be used. Moreover, there is no stability analysis for these constant current (CC)-controlled PSR flyback converters. In this article, 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 the above PWM mode, and a 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 1.92 A.

New Digital Control Method for Improving Dynamic Response of Synchronous Rectified PSR Flyback Converter With CCM and DCM Modes

In order to improve the dynamic response of synchronous rectified primary-side regulation (PSR) flyback converter with CCM and DCM modes, a novel digital control method is proposed. In a dynamic process, when output voltage is detected to fluctuate greatly, two special working modes called light-to-heavy mode and heavy-to-light mode are introduced. The output capacitor will be quickly charged and discharged by an optimized control scheme to make the output voltage's dynamic fluctuation smaller. On the other hand, during the dynamic process control, for eliminating overshoot and oscillation when the output voltage returns to the reference voltage, the load is detected by the output voltage slope to determine the appropriate operating mode. With the proposed control method, the dynamic performance can be greatly improved. An field programmable gate array (FPGA)-controlled 20-V/5-A synchronous rectified PSR flyback converter is established to verify the proposed control scheme. In the prototype test, compared to the traditional multimode control, the undershoot voltage and overshoot voltage of the proposed control scheme are improved from 5.02 to 1.63 V and 3.15 to 1.73 V, respectively. The undershoot and overshoot recovery times are reduced from 83.43 to 1.79 ms and 40.32 to 1.85 ms, respectively.

A Digital Control Scheme for PSR Flyback Converter in CCM and DCM

Due to the simple structure and low cost, the primary-side-regulation (PSR) flyback converter is widely used in small power applications. As the output voltage is sampled from auxiliary winding in PSR flyback converter, some sampling error exists, especially when continuous conduction mode (CCM) is introduced for higher power. To improve the constant voltage accuracy, a novel digital controlled sampling strategy is proposed. This scheme uses a digital ramp sampling method to sample output voltage in both discontinuous conduction mode (DCM) and CCM, and proposes a voltage adjustment strategy to adjust sampling errors in CCM without weakening the stability in the load-switch process. Finally, the experimental results validate the presented scheme and show that the output voltage error is less than 0.6% in a 20-V, 5-A PSR flyback prototype.

A Low-Cost Constant Current Control Method for DCM and CCM in Digitally Controlled Primary-Side Regulation Flyback Converter

Primary-side regulation (PSR) flyback converter with a discontinuous conduction modulation (DCM) mode is widely used in small-power applications. To introduce higher output power, a continuous conduction modulation (CCM) mode is used in which an analog to digital converter of high cost is always required. In this paper, to reduce the cost, a novel digital peak current control method is proposed to realize constant output current control in both DCM mode and CCM mode. However, there exists a time length calculation error that cannot be avoided in the critical condition between DCM mode and CCM mode. The output current will be lower than the nominal output current. Thus, a hysteretic multimode control method with two pulse width modulation modes and two pulse frequency modulation modes is utilized to eliminate the time length calculation error. In the proposed control, only a low-speed digital to analog converter and three comparators are used, which greatly reduced the cost, and high accuracy of output current can be obtained. The proposed control scheme was then verified through a field-programmable gate array (FPGA)-controlled 3.76–15 V/3.76 A PSR flyback converter. In the prototype, the accuracy of the output current is within ±1.5% for the universal load range.

Analysis of a Time-Length Compensation Algorithm for Elimination of Subharmonic Oscillation and Application in a Digitally Controlled Primary-Side Regulation Flyback Converter

Subharmonic oscillation mostly happens in the continuous conduction modulation mode. Digital slope compensation and digital reposition compensation are two digital realized compensation methods to eliminate subharmonic oscillation. In the above two methods, a fast digital to analog converter (DAC) for slope voltage shaping or an analog to digital converter (ADC) for current sampling is required. In order to reduce the cost and simplify the compensation, a matrix analysis method is first put forward to analyze the generation mechanism of subharmonic oscillation in the primary-side regulation (PSR) flyback converter with peak current control. Based on the matrix analysis method, a simple time-length compensation algorithm is presented to eliminate subharmonic oscillation. Only the switch-on time is applied to compensate the primary peak current or the switching period of the next switching cycle. No subharmonic oscillation occurs and only a low-speed DAC is required. The cost is low as the fast DAC or ADC is removed. A 48-W PSR flyback converter is implemented to verify the above analysis. Experiments prove that the matrix analysis method is feasible, and the time-length compensation algorithm is effective to eliminate subharmonic oscillation. It can be promoted to eliminate subharmonic oscillation in different control methods and other power topologies.

Novel Digital Control Method for Improving Dynamic Responses of Multimode Primary-Side Regulation Flyback Converter

In order to improve the dynamic responses of multimode controlled primary-side regulation flyback converter, a novel digital control method is proposed in this paper. A new DAC sampling method, which can capture the output voltage during dynamic transition, is introduced. Based on it, a dynamic module which can monitor the variation of the output voltage to improve the dynamic performance is proposed. In a 5-V/1-A primary-side regulation flyback converter, the maximum undershoot voltage and overshoot voltage of the proposed control scheme in this study are 0.472 and 0.192 V, respectively. They are much lower compared to 1.296 and 0.584 V in the traditional control scheme. The maximum undershoot and overshoot recovery times are reduced from 10.86 to 1.29 ms and 126.3 to 53.68 ms, respectively. The proposed control scheme was then verified by a FPGA controlled prototype.

High-Precision Digital Constant Current Controller with Demagnetization-Time Compensation for Primary-Side Regulation Flyback Converter

A novel digital constant output current controller with demagnetization-time compensation for flyback converter is proposed in this paper. The secondary winding demagnetization time [Formula: see text] is sampled from the comparison module output signal by output voltage sampling state machine. The ratio between [Formula: see text] and switching period [Formula: see text] is kept constant by bidirectional counter module to achieve constant output current based on invariable primary-side peak-current. Meanwhile, demagnetization-time compensation is proposed in order to enhance load regulation ratio. The compensation [Formula: see text] acquired from a look-up table, is utilized to compensate the impacts caused by the delay [Formula: see text] from the process of sampling the signal of [Formula: see text]. The digital controller (DC) is implemented by hardware description language Verilog HDL. Experimental results of the proposed 2A constant current output flyback converter based on FPGA(EP2C8Q208C8N) indicate that the constant current precision is within [Formula: see text]1% in a wide range of universal-input AC voltage from 110[Formula: see text]V to 240[Formula: see text]V and the voltage load range between 2[Formula: see text]V and 8[Formula: see text]V.