Design and Analysis of RCD Clamp Circuit in Flyback Converters
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This paper considers about ignored factors by past research work such as effects of forward and reverse recovery characteristics of the clamping diode and the leakage inductance Lsof the secondary side on RCD parameter design. The influence of the diode forward recovery on voltage spike of the power switch and reverse recovery on RCD clamp circuit power loss and parameter design is analyzed. Detailed analysis is given to reveal that the leakage inductance of the secondary increases the energy absorbed by the RCD clamp circuit as well as the primary leakage inductance. Meanwhile, a revised RCD parameter design method is proposed based on the existing design method, by taking consideration of forward recovery and reverse recovery characteristics of the clamping diode and the secondary leakage inductance Ls. Both simulation and experimental results validate the feasibility of the proposed design method.Keywords:
Leakage inductance
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Clamp
Leakage (economics)
Voltage spike
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In this paper, a novel active clamp Flyback-Forward converter is proposed for large voltage gain and high power applications. The interleaved configuration on the primary side is employed to handle the large input current. An improved voltage doubler configuration is adopted on the secondary side to make the output diodes sustain only half of the high output voltage. Furthermore, the output diode voltage stress can be auto-balanced due to the inherent series structure of the coupled inductors. Therefore, the low voltage stress diodes can be used to enhance the circuit performance. Moreover, the active clamp circuits can be employed to recycle the leakage energy and absorb the possible turn-off voltage spikes on the primary power devices. In addition, zero-voltage-switching (ZVS) soft switching operation is achieved for all the active switches during the switching transition. The output diode reverse-recovery problem is alleviated due to the leakage inductance, leading to a great reduction of switching losses. Finally, a 40 V-input 380 V-output 1 kW prototype is built to demonstrate the effectiveness of the theoretical analysis.
Voltage doubler
Leakage inductance
Flyback diode
Voltage spike
Peak inverse voltage
Clamper
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An active clamp high step-up boost converter with a coupled inductor is proposed in this paper. In the proposed strategy, a coupled inductor is adopted to achieve a high voltage gain. The clamp circuit is included to achieve the zero-voltage-switching (ZVS) condition for both the main and clamp switches. A rectifier composed of a capacitor and a diode is added to reduce the voltage stress of the output rectifier diode. As a result, diodes with a low reverse-recovery time and forward voltage-drop can be utilized. Since the voltage stresses of the main and clamp switches are far below the output voltage, low-voltage-rated MOSFETs can be adopted to reduce conduction losses. Moreover, the reverse-recovery losses of the diodes are reduced due to the inherent leakage inductance of the coupled inductor. Therefore, high efficiency can be expected. Firstly, the derivation of the proposed converter is given and the operation analysis is described. Then, a steady-state performance analysis of the proposed converter is analyzed in detail. Finally, a 250 W prototype is built to verify the analysis. The measured maximum efficiency of the prototype is 95%.
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Rectifier (neural networks)
Leakage inductance
Peak inverse voltage
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The fundamental limitations of the current topologies for isolated high step-up dc-dc conversion are summarized. The primary-parallel-secondary-series structure is employed in this paper to handle the large input current, sustain the high output voltage and extend the voltage gain. A novel active clamp boost converter with coupled-inductors is proposed for high step-up applications. The third windings of the coupled-inductors have the function of voltage gain extension and the switch voltage stress reduction. The active clamp circuit serves for the interleaved two phases, which reduces the circuit complexity. Both the main and the auxiliary switches of the proposed converter are zero voltage transition performances during the whole switching transition. Meanwhile, the leakage energy is recycled by the active clamp circuit. The rectifier voltage stress is reduced by the primary-parallel-secondary-series structure. The rectifier reverse-recovery problem is alleviated by the leakage inductance. Experimental results for a 40-V-to-760-V converter verify the significant improvements in efficiency.
Leakage inductance
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Clamper
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An isolated interleaved zero voltage switching (ZVS) Flyback-Forward boost type converter with active clamp scheme is designed in this paper. Both the main and the clamp switches canswitching losses operate with ZVS soft switching performance to reduce the switching losses. Furthermore, the leakage energy is recycled and the turn-off voltage spikes on the main switches are absorbed by the active clamp circuit. In addition, there are two coupled inductors in the designed converter and the secondary windings of the coupled inductors are in series to achieve boost type conversion. The coupled inductor can work in the Flyback mode when the corresponding main switch is in the turn-on state and in the Forward mode when it is in the turn-off state, which takes full use of the magnetic core and improves the power density. Experimental results verified the theoretical analysis and the effectiveness of the ZVS Flyback-Forward converter.
Flyback diode
Voltage spike
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In this paper,a novel single-stage PFC converter, which integrated a Buck-Boost converter with a Flyback converter, was presented applicable for LED lamp driver. The proposed circuit could enhance the efficiency via the innovative structure, which recycled the leakage inductance energy, alleviate voltage spike and ringing on MOSFET without a snubber circuit, improved the electromagnetic interference(EMI) and efficiency. The basic operating principle and analysis was introduced in detail and the circuit parameter was analyzed and calculated. When the Buck-Boost and Flyback worked in Discontinuous current mode(DCM), the bulk capacitor voltage was unchanged with the load, thus the high voltage stress problem was avoided. A prototype of a 8 W single-stage LED driver was built, and the correctness of theoretical analysis was validated by experiments.
Snubber
Leakage inductance
Voltage spike
Buck converter
Ringing
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In this paper, a step-up active-clamp SEPIC with bi-transformer is presented for battery sourcing application. Two voltage double circuits are connected in series at secondary side, thus, the output voltage could be increase compared with the conventional isolated SEPIC converter. The voltage double circuit at secondary side provides high voltage gain and limits the voltage spike on output diodes. The interleaved operation in output side reduces ripple current and output capacitance. The active-clamp technique is used to reduce voltage stresses on switches and achieve ZVS for main and auxiliary switches and recycle the stored energy of resonant inductance and magnetizing inductance. The leakage inductance of the transformer and additional resonant inductance are used to achieve ZVS during the dead time. Therefore, high conversion efficiency can be obtained. The analysis and design consideration of the proposed converter are shown in detail. Experimental results are shown to prove prototype with input 48V and 200V / 2A output.
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Aiming at too much voltage stress on the main switch and voltage spikes from transformer air gap leakage inductance when switching off,experimental study on the topology and operation principle of dual switch flyback were carried out.The energy transfer model of dual switch flyback in DCM was built,and the result was revealed that the transformer turns ratio impacts magnetic reset time of the primary leakage inductance which has influence on maximum duty cycle and energy returned.The design formulas on the main parameters of the dual switch flyback was deduced.With the design formulas,a 30 W dual switch flyback in DCM was designed.The Saber simulation was established,to research the operating current in main switches.The results indicate that the transformer turns ratio is appropriate and energy feedback is weakened.Some calculated results are verified by the experimental data,which shows they are reasonable.The design formulas can be used as a design tool to develop more efficient dual switch flyback.
Leakage inductance
Flyback diode
Duty cycle
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The forward power converter with a dissipative clamp reset network (RCD clamp) is widely used due to its simplicity. In this paper, the efficiency of this topology is increased by means of the incorporation of self driven synchronous rectification. The inclusion in the power stage of several MOSFETs affects the circuit performance. Design guidelines and optimization of this new topology are carried out in this work. A low output voltage (3.3 V) and high power density prototype has been built, featuring very high efficiency (87.5%) at very high switching frequency (700 kHz).< >
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In order to achieve Zero Voltage Switching (ZVS) easier for both primary switch and auxiliary switch in the active clamp forward converter,an improved active-clamp ZVS forward converter topology is proposed in this paper.Compared with the conventional active-clamp forward converter,the improved one with an auxiliary network which is consisted of a clamp capacitor and an inductor could easily achieve ZVS in full-load range.Therefore the circuit efficiency is increased by reducing the switching loss of the switches.The operation principles of the proposed converter circuit are analyzed in detail and the performance is compared with the conventional one.The design procedure and the experimental results are presented for a converter with a 230 V input,14.4 V/10 A output.The experimental results match the theoretical analysis very well.
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