Active Clamp Forward Converter Research Articles

Design of 30 A Load Current and 93% Peak Efficiency for Active Clamping Forward Converter With Complete Protection

Design of 30 A Load Current and 93% Peak Efficiency for Active Clamping Forward Converter With Complete Protection

ZVS Active Clamp 포워드 컨버터를 적용한 철도차량용 전원공급장치

ZVS Active Clamp 포워드 컨버터를 적용한 철도차량용 전원공급장치

Drain-Source Voltage-Controllable Three-Switch Active-Clamp Forward Converter for Wide Input/Output Voltage Applications.

Active-clamp forward converters are applied to various medium-capacity power systems because they have a relatively simple structure and are capable of zero-voltage switching. In particular, there is the advantage that a stable output voltage can be obtained by controlling the duty ratio of the power semiconductor switch even in applications with wide input and output voltage ranges. However, the voltage stress on the power semiconductor switches due to the application of active clamp is higher than the input voltage, especially as the duty ratio increases. A three-switch active-clamp forward converter is proposed, which can overcome such shortcomings and can reduce the voltage stress of the power semiconductor switches, but it causes an increase in the DC bias of the magnetizing current and the additional conduction and switching losses. Therefore, in this paper, a voltage-stress-controllable three-switch active-clamp forward converter that can utilize both advantages of the conventional active-clamp forward converter and three-switch active clamp forward converter is proposed and verified through a prototype for 800 W battery charger.

Optimal control of bidirectional active clamp forward converter with synchronous rectifier based cell-to-external-storage active balancing system

Active cell balancing is a more energy-efficient way of balancing cells in series comparing to passive balancing. To further improve the performance of an active balancing system, an optimal control approach can be applied to optimise the system performance indexes. This paper proposes an optimal controller for the bidirectional active clamp forward converter with synchronous rectifier (ACFC-SR) based cell-to-external-storage active balancing system to concurrently optimise the balancing speed and the energy efficiency. The formulated optimization problem does not require the complicated nonlinear converter efficiency model compared to other optimal controllers that involve efficiency model to reduce energy loss. The flexibility in changing the balancing priority of the balancing time and the converter efficiency is achieved via different weights on the objective function. The effectiveness of the proposed controller is validated experimentally with real cells and the power electronics board.

A new magnetron driving method using a phase‐shifted active clamp forward converter for sulfur plasma tube applications

This paper presents a new method for driving the magnetron for a sulfur plasma tube using the two-switch forward converter structure with a phase-shifting active clamp (1000±40 W, 285 mA, 4 kV). Depending on the output voltage level required, the magnetron driver circuit is boosted and insulated and also has high gain. The use of the two-switch forward converter reduces the transistor voltage stress. In addition, applying the clamp structure balances the magnetization current. Besides, by controlling the phase shift of the clamp transistor, while maintaining the magnetic current balance of the power transformer, the duty cycle of the main transistors can be increased. This allows more voltage level transfer to the secondary winding of the transformer. Therefore, with a fixed transformer core, more voltage transmission is possible in comparison with a conventional forward converter. Moreover, using the PFC converter improves the power factor and stabilizes the DC-link voltage. The magnetron driver circuit provides a maximum power of 1 kW with an average power of 125–250 W by adjusting the converter's active time under minimum loss conditions. The magnetron driver circuit provided is validated by the simulation and experimental results.

Two-Mode Low-Voltage DC/DC Converter With High and Wide Input Voltage Range

It has been proposed that the main battery voltage of electric vehicles should be increased to increase the driving distance and decrease the charging time. Thus, a low-voltage dc/dc converter (LDC) with high and wide input voltage range is required for electronic loads. This article proposes a two-mode LDC and the entire input range is divided into two low and high input voltage ranges. The converter has two operating modes corresponding to these input voltage ranges. In the low input voltage range, it operates as a three-switch double-ended active clamp forward converter. In the high input voltage range, it operates as an asymmetric half-bridge converter. Changing the operating mode according to the input voltage, the proposed converter can have low-voltage stresses on the switches and a low dc offset current of the transformer resulting in high efficiency for the entire input voltage range. In order to confirm the validity of the proposed converter, a 600 W prototype is implemented and experimented.

A Comparative Study of GaN HEMT and Si MOSFET-Based Active Clamp Forward Converters

Compared with conventional forward converters, active clamp forward (ACF) converters have many advantages, including lower voltage stress on the primary power devices, the ability to switch at zero voltage, reduced EMI and duty cycle operation above 50%. Thus, it has been the most popular solution for the low bus voltage applications, such as 48 V and 28 V. However, because of the poor performance of Si MOSFETs, the efficiency of active clamp forward converters is difficult to further improved. Focusing on the bus voltage of 28 V with 18~36 V voltage range application, the Gallium Nitride high electron-mobility transistors (GaN HEMT) with ultralow on-resistance, low parasitic capacitances, and no reverse recovery, is incorporated into active clamp forward converters for achieving higher efficiency and power density, in this paper. Meanwhile, the comparative analysis is performed for Si MOSFET and GaN HEMT. In order to demonstrate the feasibility and validity of the proposed solution and comparative analysis, two 18~36 V input, 120 W/12 V output, synchronous rectification prototype with different power devices are built and compared in the lab. The experimental results show the GaN version can achieve the efficiency of 95.45%, which is around 1% higher than its counterpart under the whole load condition and the same power density of 2.2 W/cm3.

Modeling of high-side active clamp forward converter with resistive parasitics

Purpose The purpose of this paper is to derive the small-signal/canonical model derivation of the high-side active clamp forward converter (ACFC) with diode rectification for ideal and with resistive parasitics. It also covers the analysis of ACFC small-signal model with resistive parasitics using computer-aided modeling software Personal Computer Simulation Program with Integrated Circuit Emphasis (PSPICE) 16.6. The effects of variation of system parameters on the ACFC’s state transfer functions and operations have been highlighted in this paper. Design/methodology/approach The large-signal model and small-signal model of the ACFC with diode rectification has been derived using AC small-signal modeling approach. Findings The operating point of the converter changes with the consideration of resistive parasitics compared with the ideal case. The response obtained from the hardware matches with the time domain response of the averaged model and switch model developed in PSPICE. Research limitations/implications This paper limits the study of ACFC small-signal behavior by using computer-aided design software PSPICE. The dead time of the converter is not considered because it is negligible when compared with the on and off time. The leakage inductance which plays a role in zero voltage switching of the ACFC switches is neglected in the analysis as it is very small compared to the magnetizing inductance. The switching losses are not considered in the modeling. Practical implications The mathematical computation of deriving the system transfer functions from canonical model is complex and time consuming. Originality/value The modeling with resistive parasitics improves the effectiveness of the equivalent model. Also, the analysis with computer-aided modeling software PSPICE gives reliable results in less time.

Power Loss Analysis of Bidirectional ACFC-SR Based Active Cell Balancing System

With the expansion of the number of electric vehicles (EV) over the world, the research on the battery and the battery management system (BMS) have become more popular. The active balancing, which is working as an advanced function in the modern BMS, has attracted researchers’ attention to enhance battery system performance and prolong the battery pack life via integration of specially designed power electronic circuit with proper control and optimisation strategies in the BMS. This paper develops the power-loss and efficiency models of the bidirectional active clamp forward converter with synchronous rectifier (ACFC-SR) based active cell balancing system. The developed models can be involved in the power loss analysis of the active cell balancing system to underpin the energy efficiency performance evaluation and the balancing control system design of active balancing systems. The optimal balancing current with which the converter would operate at the maximum efficiency point can be obtained via the developed efficiency model. A case study is also included to illustrate the efficiency performance of the active balancing system.

Interleaved centre clamped forward converter (ICCFC) for wide input voltage range applications

A new interleaved centre clamped forward converter for high current applications is proposed. It is a series input and series output structure with common active clamp reset branch. In the proposed converter, both the high input voltage stress and output current stress are reduced. The converter comprises of two active clamp forward converters with one common centre clamp reset circuit and the series output comprises of a current double rectifier (CDR) with self-driven synchronous rectifier (SDSR). The capacitor divider at the input reduces the switching stress due to input voltage. The common centre clamp circuit enables the transformer core reset without any additional circuit and enables zero volt switching. The SDSR-based CDR reduces burden on the secondary side of the transformer by an additional current sharing. Extended duty cycle beyond 50% is achieved. Overall reduction in the size of magnetic components with reduced part count and high-power density is attained. Prototype for 50 W with input voltage in the range of 50—200 V, 5 V/10 A output at 100 kHz was developed. The experimental results match the theoretical investigations.

Active-Clamp Forward Converter With Lossless-Snubber on Secondary-Side

This paper proposes a novel active-clamp forward converter (ACFC) with a lossless-snubber on the secondary-side, which combines a resonant capacitor and a clamping diode with an output inductor in parallel. The conventional ACFC achieves zero-voltage-switching on switches of the primary-side during dead time for reducing the switching loss and voltage spike. Unfortunately, on the secondary-side of transformer, the voltage spike damages the free-wheeling diode and rectifier diode due to the reverse recovery current and junction-capacitor of the diode and leakage inductance of the transformer. This paper proposes a lossless-snubber on the secondary-side operation for reducing the voltage spike on the free-wheeling diode and forward-rectifier diode. Therefore, the converter proposed in this paper is suitable for high-output-current applications. Experimental results are shown to verify the analysis and design procedure of the proposed forward converter.

A 12- or 48-V Input, 0.9-V Output Active-Clamp Forward Converter Power Block for Servers and Datacenters

DC-to-DC power supplies are critical components for processors in high performance computing and datacenter servers. Conversion from an intermediate bus voltage (e.g., 12 or 48 V) to the core voltage (∼0.9 V) of processors must be efficient, compact, and cost effective. This paper proposes two versions of active-clamp forward converter (ACFC) power blocks to supply core voltage from either 12 or 48 V intermediate bus voltage. The ACFC power block can be individually tested prior to assembly and vertically soldered onto the motherboard to fit in a standard 1U server. A low loss, compact planar transformer is designed into the ACFC power block printed circuit board (PCB). A custom, standing slab inductor not only provides high inductance and high saturation current but also helps to mechanically support the power block. A one-piece copper winding connects the transformer to the inductor, thereby reducing the dc loss in the current path. Thorough analysis is performed to model the conversion loss of the proposed power block. Experimental results show a peak efficiency of 90.4% (12 V input) and 89.5% (48 V input) with 0.9-V output.

An Interleaved Active-Clamp Forward Converter Modified for Reduced Primary Conduction Loss Without Additional Components

This paper proposes an interleaved active-clamp forward (IACF) converter modified for high efficiency without any additional component. To employ high input voltage, the components on one active-clamp forward module are re-arranged from the conventional IACF converter. The proposed converter can significantly reduce the primary conduction loss with large turns-ratio of the transformer due to the higher input voltage of the modified module and the expanded duty ratio at the nominal input voltage. In addition, unlike the existing approaches, the power density is not affected because there is no additional component. Finally, the proposed converter is validated experimentally using a prototype converter with 36–72 V dc input and 480 W (12 V dc/40 A) output.

Multi-Winding Configuration Optimization of Multi-Output Planar Transformers in GaN Active Forward Converters for Satellite Applications

It is a serious challenge to find the optimal winding configuration that realizes minimum leakage inductance of multi-output multi-winding planar transformers due to the complex coupling relationship. The proposed idea is to build the mathematical model of leakage magnetic field energy and screen out all possible winding configurations to solve the minimum value with MATLAB programming. Then, only limited potential winding configurations need to be three-dimensionally simulated in Maxwell. By analyzing the inductance matrix, the leakage inductance of multi-winding planar transformers is solved. A full gallium nitride (GaN) active clamp forward converter with self-driven synchronous rectifiers (SRs) is presented with complete mode analysis. It is noted that the proposed active clamp technology uses the auxiliary winding with the nonfloating GaN switch compared to the conventional high-side clamping circuit, which is important for the satellite applications. The GaN drive chips for high reliable gate voltage are combined with self-driving. Considering the leakage inductance in each winding and junction capacitance of the GaN high electron mobility transistors, the oscillation frequency and amplitude over the switches are modeled quantitatively, which is important to minimize powertrain loop at MHz. The explanation of the root cause of the voltage spike in the converter is also presented. A prototype with 1 MHz, 100 V input, 5 V/6 A and ±12 V/0.83 A outputs was built to verify the proposed techniques.

Interleaved Active Clamp Forward Converter With Extended Operating Duty Ratio by Adopting Additional Series-Connected Secondary Windings for Wide Input and High Current Output Applications

This paper presents a new interleaved active clamp forward converter for low and wide input, and high current output applications. In the proposed converter, the operating duty ratio can be extended over 0.5 due to the additional powering path resulting from additional series-connected secondary windings from each transformer. As a result, the proposed converter can be designed with large transformer turns ratio. Thus, since the proposed converter can reduce not only the primary RMS current but also switch turn- off current, it can achieve high efficiency. Moreover, since all secondary switches can operate without floating gate drivers, the proposed converter can maintain simple structure and low complexity of gate driving circuits in the secondary side. The validity of this proposed converter is verified by the experimental results from 36V–72 V input and 12 V/500 W output for the dc/dc prototype.

Double-Ended Active-Clamp Forward Converter With Low DC Offset Current of Transformer

The double-ended (DE) active-clamp forward (ACF) converter is one of the attractive dc-dc converters for the power supply of digital devices due to a simple structure and zero voltage switching (ZVS) capability of primary switches. However, due to a dc offset current of transformer, the size and core loss of transformer are increased. In this paper, a new DE-ACF converter having an additional switch and a diode is proposed to achieve a low dc offset current of transformer by charging a clamp capacitor additionally during a turn-off interval between main switches. Thus, the transformer size can be reduced in the proposed converter. Furthermore, since the output inductor current ripple is reduced, the primary and secondary conduction losses can be decreased under medium and heavy loads. As a result, the proposed converter can have higher efficiency than conventional DE-ACF converter. The validity of the proposed converter is confirmed by experimental results from a prototype with 400 V nominal input voltage and 400 W (12 V/33.33 A) output.

A 30-W 90% Efficiency Dual-Mode Controlled DC–DC Controller With Power Over Ethernet Interface for Power Device

A dual-mode controlled dc–dc controller with power over Ethernet (PoE) interface for power device (PD) is presented that is designed to support drawing power either from an Ethernet cable or from an external auxiliary supply support (ASS). PoE interface supports all the functions that comply with the IEEE802.3af/at standard. Based on bandgap reference structure, a detection comparator is provided to detect input voltage without extra voltage reference. Using a low offset voltage amplifier, a low-loss current-limiting technique is proposed to achieve a high-precision current-limit point. Based on a high-speed comparator and two timing capacitors, an oscillator (OSC) is implemented for better accuracy, and provides the maximum duty cycle ( $D_{\mathrm {max}}$ ) and external frequency synchronization. The chip is fabricated in a 0.5- $\mu \text{m}$ 65 V BCD process and occupies a die size (with pads) of $1.79 \times 2.76$ mm2. The experimental results are measured for an active clamp forward converter with a wide range of dc input voltages from 33 to 57 V, an output voltage of 12 V, and an output power of 30 W. The chip achieves peak power efficiency of 90% and 90.63% on DC and ASS, respectively. The load regulation at different input voltages can be measured to be within ±0.11%. Measurements further show that the peak-to-peak ripple voltage of the chip is 161 mV and the recovery time is less than 1.2 ms for the 2-A load step.

Center Clamped Forward Converter for High Current Applications

High current applications like Microprocessors, Fuel cells, Electric Hybrid Vehicles, Solar Cells etc., use interleaved isolated buck derived converter. Interleaving of converters for such high current applications converters is done to achieve reduced input capacitor ripple voltages, output capacitor ripple current cancellation and reduced peak currents of output inductors. Generally, interleaving requires a higher number of transformers through which distributed magnetics can be achieved. i.e., one bulky transformer can be replaced with low power profile transformers. The performance of forward converter depends on core resetting of the main transformer. The core’s magnetizing energy is recycled by resetting it. In the absence of core reset, the current builds up at each switching cycle, saturates the core, causes reverse recovery problem in the diode and the active clamp will no longer in zero voltage state during turn on of the main switch. The transformer secondary output is used as a gating pulse for Synchronous Rectifiers. These have very low forward drop which are most suitable for high current applications. Among various used clamping methods, the transformer core is optimized effectively by Active center clamp reset approach. The proposed method results in less number of switches and clamping capacitor, and lower cost compared to conventional forward converter. Reduction in voltage stress without losing duty-cycle ratio is also achieved by means of a series-parallel connected switch structure with Self Driven Synchronous Rectifiers. The proposed center clamp converter overcomes the Maximum Duty cycle limitation of 50%. This paper mainly focuses on active center clamp forward converter and is also compared with Active Positive Negative clamping techniques.

A Dual-Transformer Active-Clamp Forward Converter With Nonlinear Conversion Ratio

This paper proposes a dual-transformer active-clamp forward converter (DT-ACFC) with nonlinear conversion ratio (NCR), which combines two forward converter units. Since only two active switches are needed, the cost and the circuit complexity can be lowered. To reduce switching loss, the proposed converter fulfills zero-voltage switching by employing the leakage inductance of the transformer and additional resonant inductance. By paralleling the transformer secondaries and changing the circuit architecture of each secondary side, we can make the output load current evenly shared among four output inductors such that the current stress and conduction losses of the output rectifiers can be decreased significantly. Moreover, the nonlinear step-down conversion ratio leads to a high duty utilization ratio for the proposed converter. Therefore, the DT-ACFC with NCR is suitable for applications of high output current and a wide input voltage range. Experimental results are shown to verify the theoretical analysis of the proposed forward converter.

Analysis, Design, and Implementation of a Soft-Switched Active-Clamped Forward Converter with a Current-Doubler Rectifier

This study examines the zero-voltage switching (ZVS) operation of an active-clamped forward converter (ACFC) with a current-doubler rectifier (CDR). The ZVS condition can be obtained with a much smaller leakage inductance compared to that of a conventional ACFC. Due to the significantly reduced leakage inductance, the design is optimized and the circulating loss is reduced. The operation of the ACFC with a CDR is analyzed, and a detailed ZVS analysis is conducted on the basis of a steady-state analysis. From the results, a design consideration for ZVS improvement is presented. Loss analyses of the converters shows that enhanced soft-switching contributes to an efficiency improvement under light-load condition. Experimental results from a 100-W (5-V/20-A) prototype verify that the ACFC with a CDR can attain ZVS across an extended load range of loads and achieve a higher efficiency than conventional ACFCs.