Current-Sharing Active-Clamped Forward Power Converter with Self-driven Synchronous Rectifier

Many DC-DC converters use soft-switching techniques with active-clamp snubber in order to reduce switching surge and common-mode noise. In particular, common-source type active-clamped DC-DC converter is one of the most useful circuit topology for reduction of common-mode noise. Furthermore, in low-voltage and large-current DC-DC converters, synchronous rectifier circuits are used to improve the power efficiency. self-driven synchronous rectifier circuits are generally used because of isolation and easy control. Recently, it has been noticed that an abnormal phenomenon occurs under some conditions in the common-source type forward converter with self-driven synchronous rectifier circuit. This paper describes the analysis of this abnormal phenomenon and clarifies the conditions of the abnormal phenomenon with experimental results.

The clamped-mode (CM) forward zero-voltage-switching multi-resonant power converter (ZVS-MRC) with a self-driven synchronous rectifier is studied. The loss at the synchronous rectification stage of the power converter is analyzed and compared with the loss at the conventional Schottky diode rectification stage of the power converter. From the results of the analysis, it is known that the use of MOSFETs as a synchronous rectifier effectively reduces the loss at the rectification stage over the whole load range. In order to verify the validity of the analysis, the authors have built a 33 W (3.3 V/10 A) CM forward ZVS-MRC with a self-driven synchronous rectifier, with a switching frequency of 1 MHz, and tested its performance. From these experimental results, synchronous rectification achieved about a 3 W improvement in losses at the rectification stage and about 3% in the efficiency of the power converter as compared with conventional Schottky diode rectification.

In order to comply with IEC-1000-3-2, a single stage AC-to-DC half-bridge with complementary-control (HBCC) converter with an active input current shaper (AICS) is proposed in this paper. The principle of operation of the AICS is based on a proposed input current shaping method (the series connection of a voltage source and a loss-free resistor between the input rectifier and the bulk capacitor). Moreover, the HBCC converter presents excellent features for low output voltage conversion due to the fact that it is possible to use self-driven synchronous rectification on it. In this paper, both the HBCC and the AICS are combined to obtain a single stage AC-to-DC converter that complies with IEC 1000-3-2 regulations with a high efficiency and at a very low cost.

Nowadays, as the demand of portable electric products is increased, that of adaptors, which charge the battery of portable electric products or supply power, is also increased. Key issues of portable electric products are power density, temperature, average efficiency and stand-by power. Many isolated DC/DC converter topologies suitable for high power density is presented [1]∽[3]. All of them try to reduce size and cost by minimizing the number of components. Generally, converter topologies which have no output-inductor for DC/DC converter is suitable for high power density application. Active clamp flyback converter and output-inductor-less forward converter are representative converters without output inductor. However, these converters have critical problems. In active clamp flyback converter, DC offset current which degrades transformer utilization and makes transformer bulky. Therefore it causes low power density. In the other side, output-inductor-less active clamp forward converter has high RMS value of current which causes heat problem. This paper proposes an output-inductor-less active clamp forward converter employing current boost-up circuit for adaptors. Due to applying the proposed current boost-up circuit, the proposed converter has low conduction loss and low voltage ringing of the secondary rectifier. This paper presents the operational principle and design consideration of the proposed converter. Experimental results are demonstrated to verify the feasibility and advantages of the proposed converter.

This paper presents the principles and performance of peak current mode control applied to active clamp forward converter in comparison to the conventional voltage mode control. There is a clamp circuit comprising one auxiliary switch and one clamp capacitor, used in the forward converter to recycle the energy stored in the transformer. Due to presence of clamp circuit the active clamp forward converter with center tapped secondary exhibits fourth order power stage dynamics. When conventional voltage mode control is adapted, the forth order power stage dynamics imposes limitations on the closed loop performance of the converter. It is demonstrated that current mode control can be adapted to enhance the closed loop performance of active clamp forward converter. Different transfer functions are derived using state space average model. The peak current mode control is applied and simulation results are presented.

This paper presents the control to output transfer function, principles and performance of peak current mode-controlled active clamp forward converter with centre-tap transformer. There is a clamp circuit comprising of one auxiliary switch and one clamp capacitor, which is used in the forward converter to recycle the energy stored in the magnetising inductor. Due to presence of clamp circuit, the active clamp forward converter with centre tap transformer exhibits fourth-order power stage dynamics. The current mode control is implemented to enhance the performance of the converter by sensing the main switch current. It is demonstrated that current loop gain splits not only the complex-conjugate pole of the output filter but also the complex-conjugate pole pair formed by clamp circuit into real poles. Different transfer functions are derived using state space average model. The peak current mode control is implemented experimentally using controller IC, UCC2891D, and the simulation results are verified with the experimental setup.

<p>This research paper presents the design issues of digital Controllers for Forward Converter with Active Clamp circuit (ACFC). Brief review of Working Principle and mathematical modelling of the converter is first given. The importance of Digital Controllers for forward converter and design procedure is described in detail. And the validity of designed controllers and achievement of desired compensation is verified by the results of implemented digital controllers to Active clamp forward Converter (ACFC). Finallly results are analyzed by applying disturbances at both supply end and Load ends of the converter. And the conclusions are made based on obtained results of Voltage Mode Controller (VMC) by comparing with the results of the Current Mode Controller (CMC).</p>

This paper presents a high efficiency half-bridge DC-DC converter for an LED backlight drive system of LCD module inspection equipment. The proposed converter improves the converter efficiency using characteristics of the asymmetrical half-bridge converter and the self-driven synchronous rectifier, and thus improves the total efficiency of the LED backlight drive system. The synchronous rectifier applied to the proposed converter is the new topological synchronous rectifier, which changes slightly the transformer structure and the synchronous switch connection in the asymmetrical half-bridge converter with a conventional self-driven synchronous rectifier. Since the proposed converter utilizes the transformer leakage inductor as its resonant inductor, its structure is simplified. The proposed converter well operates under the universal DC input voltage (<TEX>$250{\sim}380V$</TEX>). The operational principle and a design example for a 100W prototype are discussed in detail, respectively. Experimental results are shown for the designed prototype converter under universal DC input voltage.

This paper proposes a high-efficiency zero-voltage-switching (ZVS) AC-DC light-emitting-diode (LED) driver. The structure of the proposed converter is based on a buck-boost power-factor-correction (PFC) converter. Through replacement of an output diode with a self-driven synchronous rectifier (SR), the conduction loss decreases significantly, and there is no switching loss because of the ZVS operation of the switching devices. In addition, no additional control circuit is required and cost reduction is achieved because the SR is self-driven. The efficiency of the proposed converter is higher than that of the conventional critical-conduction-mode (CRM) buck-boost PFC converter, owing to the reduced conduction loss of the high-side output rectifier and no switching loss of either of the switches. For verifying the ZVS operation and efficiency improvement of the proposed AC-DC LED driver, theoretical analysis and experimental results of a 48-[V] and 1.4-[A] prototype for LED driver are discussed.

A new self-driven MOSFET synchronous rectifier in a forward converter is presented. This topology is realized by adding only a few components to the conventional synchronous rectifier. MOSFETs are driven by the optimum waveforms and the operation is very simple. High efficiency has been achieved in an actual circuit. The efficiency is improved about 1.5% (5 V, 10 A) by the new configuration compared to the forward topology with active clamp technology.

For power supplies of communication system, we propose an active-clamped zero-voltage-switching (ZVS) forward converter with a synchronous rectifier. This converter was designed and fabricated, and the power conversion efficiency was compared with a conventional forward converter having a reset winding with synchronous rectifiers. Here, they were operated on the conditions of input voltage of DC 48 V, output voltage of 5 V, output current of 10 A and switching frequency of 120 kHz. As a measurement result, the conversion efficiency of the proposed converter was 90.6% and it was average 3.1% higher than the conventional forward converter having a reset winding with synchronous rectifiers. If major components of a converter are carefully chosen by considering the switching characteristics and the driving circuit for ZVS is more stabilized, this proposed converter can be used to realize the converter with output voltage lower than 3.3 V, higher conversion efficiency, and higher output current.

A new multiple-coupled inductor (MCI) is proposed for good cross regulation among low output voltages, high power density, and reduced converter volume. Moreover, a current doubler rectifier and a self-driven synchronous rectifier are presented to achieve high efficiency. The structure of the MCI is composed of four windings on a common core, and has the properties of a current doubler and good cross regulation. A dc-dc half-bridge converter using the proposed MCI is analyzed and designed for 40-W low output voltages (3.3, 4.5 V). This converter is very suitable for high current and low voltage applications. It is shown via experimental results that efficiency of over 90% and cross regulation of about 5% are achieved

In this study, a new zero‐voltage switching (ZVS) output inductor‐less bidirectional forward (OILBF) converter is presented. The OILBF has two diodes less than the conventional forward converter and is convenient for low‐power bidirectional applications. Moreover, the OILBF converter uses the leakage inductance of transformer as the forward inductor. In the proposed OILBF, two capacitors paralleled with main switches realise ZVS conditions for main switches in both directions without any auxiliary switches. Also, the reset of the converter transformer is done without any additional circuit. The proposed converter structure due to employing simultaneously OILBF topology with the simple auxiliary soft‐switching circuit is simple and low cost. The ZVS soft‐switching range is from light load to full load which enhances the converter efficiency. Phase shift is applied with the proposed converter. The proposed converter is completely analysed and its design approach is considered. Finally, an experimental prototype is implemented to verify theoretical results.

A novel dual-switch forward converter with input current ripple reduction, one of Taiwan Tech converters, is derived from a tertiary-winding forward converter by inserting a clamping capacitor between two identical primary windings and modifying with two series-connected MOSFETs and diodes. Lossless snubbing, voltage clamping, voltage sharing, and input current ripple reduction features are obtained under steady-state and transient conditions. Moreover, low voltage rating MOSFET accompanied with lower equivalent RDS(on) results in the reduction of the conduction losses. Furthermore, the reduced EMI filter components can be used to meet the EMI regulation due to the reduction of the pulsating input current-ripple. Consequently, it is suitable for high input-voltage, high efficiency, and high power density power conversion applications. To demonstrate its feasibility, the operation principle and the experimental results of the proposed converter with 300–400 V input and 50V/5A output power are described.

This paper presents a zero voltage and zero current switching (ZVZCS), dual, two-transistor forward converter (DTTFC) for high input voltage and high power application. Two identical two-transistor forward converters (TTFC) are connected in series and coupled through a single transformer using two primary windings, because of which it operates like a full bridge and makes it suitable for high power application. It imposes only half the input voltage across each of the four switches. This DTTFC has advantage of high reliability as compared to the full or half bridge converters. A modified pulse width modulation (PWM) controller is proposed for DTTFC to minimize the circulating RMS current flowing through the transformer and switching devices. This is without any extra hardware in series with primary of the transformer or in secondary. Conduction losses, being proportional to the square of the conducting current in a transformer and MOSFET, are important in high power converters operating at high currents. Since switching losses are also important in high frequency switching application, in DTTFC two switches, out of four switches, are turned-on and off at zero voltage condition due to the current in leakage inductance of a transformer. The remaining two switches are turned-off at zero voltage and turned-on at zero current condition due to transformer leakage inductance and minimized circulating current, over a wide range of load current. The advantages of this simple circuit topology is high efficiency, high reliability, low component count, and low cost, makes the new converter attractive for high input voltage, high power applications. In this paper we discuss the operating states, switching transitions, method of control, experimental results and associated waveforms of a MOSFET based practical 60 V, 50 A, 100 kHz, dual, two-transistor forward DC-DC converter operating at 750 V input bus. The measured efficiency was 95.07% at full load with maximum efficiency of 96.6% at 70% load.