Output Capacitance Of Switches Research Articles

Complete ZVS Analysis in Dual Active Bridge

Zero-voltage-switching (ZVS) has been widely applied in widebandgap devices based on high-switching-frequency converters, for instance, dual-active-bridge isolated dc-dc converter, which consists of two H-bridges. To secure ZVS for all eight switches, previous literature mostly focuses on half-bridge to analyze switching transitions, which, however, is rather incomplete due to ignoring the impact of modulation strategies and cannot fulfill all circumstances. In this letter, the whole H-bridge is used as a unit to analyze the ZVS transient process, addressing the ZVS setting in different modulation strategies. The minimal initial inductor energy to complete the ZVS process is also quantified, which in return can reduce the transformer current, thereby enhancing the efficiency. Furthermore, the accurate ZVS transition time is derived incorporating with the nonlinearity of switch output capacitance, which can be further used to set the dead-band time. An H-bridge prototype with SiC devices is built up to verify the theory proposed in this letter.

A Family of Zero-Voltage-Switched Resonant Converters: Derivation, Operation, and Design

Soft switching based on resonant operation, through mitigating switching loss and alleviating electromagnetic interference, is essential to high-frequency operation to achieve high power density. To overcome the obstacles of high switch voltage stress and ease the contradiction between voltage stress and conduction loss for traditional single-switch resonant converters, a family of zero-voltage-switched (ZVS) isolated resonant converters is proposed which utilizes a novel resonant switch. The converters enable parasitic components, including transformer leakage inductance, switch output capacitance, and diode junction capacitance to act as a part of resonant components, which facilitates ZVS and zero-current-switching operation and pushes up switching frequency. The specific derivation of the topologies is expounded, and one of the proposed converters is taken for example to perform in-depth analysis, whose mode analysis, operation principles, and parameter design method are minutely presented. Synchronous rectification is employed to further improve efficiency. A prototype was built in the laboratory and the experimental results validate the theoretical analysis well.

Semiconductor-Based Galvanic Isolation: Touch Current Suppression

This paper presents a comprehensive analysis of the generation mechanism and suppression methods of common-mode (CM) touch current when employing semiconductor-based galvanic isolation (SGI). SGI achieves galvanic isolation by utilizing semiconductor switches to deliver differential-mode (DM) power during their on states while sustaining CM isolation voltage during their off states. In SGI converters, the touch current (TC) is generated as the switch output capacitance is charged by the CM voltage during each turn- on transient. The TC rises as the switching frequency increases, which limits the system power density. This process is modeled by the proposed high-frequency pulse current model and the low-frequency equivalent resistance-based average model. Passive TC suppression approaches are reviewed, and an active TC compensation method has been proposed. A 2-kW EV battery charger with a GaN-based Totem-pole power factor correction stage and an SGI-based dc/dc stage has been built and tested. The touch current has been effectively reduced by 27 dB. It allows the converter to operate at a higher switching frequency to achieve higher power density while meeting the safety standards’ touch current requirement.

Design Guidelines for a Capacitive Wireless Power Transfer System with Input/Output Matching Transformers

A capacitive wireless power transfer (C-WPT) system uses an electric field to transmit power through a physical isolation barrier which forms a pair of ac link capacitors between the metal plates. However, the physical dimension and low dielectric constant of the interface medium severely limit the effective link capacitance to a level comparable to the main switch output capacitance of the transmitting circuit, which thus narrows the soft-switching range in the light load condition. Moreover, by fundamental limit analysis, it can be proved that such a low link capacitance increases operating frequency and capacitor voltage stress in the full load condition. In order to handle these problems, this paper investigates optimal design of double matching transformer networks for C-WPT. Using mathematical analysis with fundamental harmonic approximation, a design guideline is presented to avoid unnecessarily high frequency operation, to suppress the voltage stress on the link capacitors, and to achieve wide ZVS range even with low link capacitance. Simulation and hardware implementation are performed on a 5-W prototype system equipped with a 256-pF link capacitance and a 200-pF switch output capacitance. Results show that the proposed scheme ensures zero-voltage-switching from full load to 10% load, and the switching frequency and the link capacitor voltage stress are kept below 250 kHz and 452 V, respectively, in the full load condition.

A Novel Choice Procedure of Magnetic Component Values for Phase Shifted Full Bridge Converters with a Variable Dead-Time Control Method

Magnetic components are important parts of the phase shifted full bridge (PSFB) converter. During the dead-time of switches located in the same leg, the converter can achieve zero-voltage-switching (ZVS) by using the energies stored in magnetic components to discharge or charge the output capacitances of switches. Dead-time is usually calculated under a given set of pre-defined load condition which results in that the available energies are insufficient and ZVS capability is lost at light loads. In this paper, the PSFB converter is controlled by variable dead-time method and thus full advantage can be taken of the energies stored in magnetic components. Considering that dead-time has a great effect on ZVS, the relationship between available energies and magnetic component values is formulated by analyzing the equivalent circuits during dead-time intervals. Magnetic component values are chosen based on such relationship. The proposed choice procedure can make the available energies greater than the required energies for ZVS operation over a wide range of load conditions. Moreover, the burst mode control is adopted in order to reduce the standby power loss. Experimental results coincide with the theoretical analysis. The proposed method is a simple and practical solution to extend the ZVS range.

1.5kW 연료전지 복합발전 시스템의 듀얼 컨버터 설계

In this paper, parallel input / serial output dual converter is designed appropriately for fuel cell hybrid power system. In case of proposed converter, zero voltage switching condition is designed without additional resonance device using leakage inductance of transformer and output capacitance of switch, and zero voltage switching method is used. Also, the system method is for increasing power by connecting half-bridge in parallel and increasing output voltage by connecting secondary output of transformer in serial. Through this method we can increase power and decrease volume of system. So in this paper, dual converter is designed. 1.5㎾ fuel cell hybrid power system was implemented, and system operation and stability was verified through experiment.

Analysis, design and experimentation of an interleaved active-clamping buck-type converter

An interleaved pulse-width modulation (PWM) zero voltage switching (ZVS) converter is presented in this article. Two converter modules with an interleaved PWM scheme are used in the proposed circuit to achieve load current sharing and to reduce the ripple currents on the input and output capacitors such that the size of the output choke and capacitor is reduced. For each module, two buck-type dc–dc converters with only two switches are used to reduce the current rating of transformer winding and share the load current. Two buck-type converters in each module use the same switching devices to regulate the output voltage. The ZVS turn-on of the switches is achieved by utilising the transformer leakage inductance and output capacitance of switches. Thus, the switching losses of the proposed converter are reduced. Experiments based on a 660 W prototype are provided to verify the theoretical analysis and the effectiveness of the proposed converter.

Analysis of an integrated flyback and zeta converter with active clamping technique

An integrated converter with active clamping technique to achieve zero voltage switching (ZVS) is presented. In the proposed converter, the flyback and zeta topologies are used in the input and output sides to achieve the following features: to share the power switches in the transformer primary side, to achieve the partial magnetising flux reset and to share the load current. The input power is delivered to the load by the interleaved operation. The active clamping circuit, besides contributing to reduce commutation losses, resets the energy stored in the leakage inductances of both converters and the magnetising inductance of the zeta converter. The magnetising inductance of the flyback converter is reset by the load. Based on the resonance with the resonant inductance and output capacitance of switches, switches can be turned on at ZVS during the transition interval. Experimental results, taken from a laboratory prototype rated at 360 W, input voltage of 200 V, output voltage of 12 V and switching frequency of 125 kHz, are presented to demonstrate the converter performance.

Active-clamp ZVS converter with step-up voltage conversion ratio

This article presents the circuit implementation and design considerations of a zero voltage switching (ZVS) converter with voltage step-up for battery-based applications. An active-clamp circuit including one auxiliary switch and one clamp capacitor is connected in parallel with the main switch to allow resonant behaviour by the output capacitances of switches and transformer leakage inductance during the transition interval. Thus, the ZVS turn-on of switches can be achieved. The switching losses and thermal stresses of the semiconductors are reduced. The circuit configuration, operation principle and design considerations of the converter are discussed in detail. Finally, experiments conducted on a laboratory prototype rated at 200 W are provided to verify the theoretical analysis and the effectiveness of the proposed converter.

Challenges in SiC power MOSFET design

The impact of fundamental and technological parameters is considered for SiC power MOSFETs. The wide bandgap nature of SiC increases the surface electric field by 2× at inversion compared to silicon, placing an important role on surface roughness in reducing the field-effect mobility. The presence of interface-trapped charges also acts to reduce the channel mobility and increases the sensitivity of the threshold voltage to temperature. The high critical electric field of SiC increases the stored energy in the switch output capacitance by 10× compared to silicon. For hard-switched converters, it is important to design SiC MOSFETs with a high saturation current to enable high-speed turn-on transients required to discharge the integral drain-source capacitance.

Analysis of Parallel-Connected Asymmetrical Soft-Switching Converter

A new half-bridge converter with two current-doubler rectifiers is proposed. Two transformers are used in the proposed converter. The primary windings of two transformers are connected in series to reduce the voltage stress across the magnetizing inductor, since each magnetizing inductor voltage is equal to one half of the input voltage. Two current-doubler rectifiers at the secondary sides are connected in parallel to reduce the current stress of secondary winding since the secondary winding current is less than one half of the load current. The asymmetrical pulsewidth-modulation technique is used in the proposed converter to regulate the direct current output voltage. The transformer leakage inductance and the output capacitance of switching switches are resonant during the transition interval between two switches in order to achieve zero voltage switching. The operation principle and design considerations of the proposed converter are provided. Experimental results for a 100-W (5 V/20 A) prototype are presented to verify the theoretical analysis and circuit performance

An Improved Magnetic-Coupled AC-PDP Sustain Driver With Dual Recovery Paths

A cost-effective magnetic-coupled ac plasma-display-panel sustain driver with low switching loss is proposed. The transformer yields current-stress reduction of energy-recovery switches, which affects circuit cost and reliability, and its turns ratio can be used to adjust the sustain-pulse slopes affecting gas-discharge uniformity. Dividing the recovery paths, the switching loss of the recovery switches is reduced by preventing abrupt change of the switch output capacitance charge current. In addition, the proposed circuit has a simpler structure because it does not use the recovery-path diodes, which should afford a large recovery current. By reducing the current stress and device count of the energy-recovery circuit, the proposed driver may help bring the circuit cost down and improve circuit reliability

Analysis and implementation of a soft switching interleaved forward converter with current doubler rectifier

A soft switching interleaved forward converter with current doubler rectifier is presented. Active clamp circuit is used in the primary winding of transformers to recycle the energy stored in the leakage inductor and the magnetising inductor so that the voltage stresses of switches are reduced. The leakage inductance of transformers, the magnetising inductance and the clamp capacitance are resonant to achieve zero-voltage switching (ZVS) of clamp switches. The resonance between the leakage inductance of transformers and output capacitance of switch will achieve ZVS operation for the main switches in the proposed converter. The interleaved operation can reduce the current ripple on the output capacitor. Two current doubler rectifiers with ripple current cancellation are connected in parallel at the output side to reduce the current stress of the secondary winding of the transformer. All these features make the proposed converter suitable for the DC–DC converter with high output current. The operation principle and system analysis of the proposed converter are provided in detail. Finally, experimental results, taken from a laboratory prototype rated at 125 W, are presented to verify the feasibility of the proposed converter.

Analysis and implementation of ZVS forward converter with centre-tapped rectifier

The system analysis and circuit implementation of a ZVS forward converter with centre-tapped rectifier are presented. To reduce the voltage stress of the active switch in the forward converter, one auxiliary switch and one clamp capacitor are used in the adopted converter to recycle the energy stored in the transformer leakage. The resonant circuit based on the output capacitance of switches and leakage inductance of the transformer will achieve zero-voltage-switching turn-on for both switches in the adopted converter to increase the total circuit efficiency. The centre-tapped rectifier is used at the secondary side to achieve full-wave rectifier. In high output current applications, the synchronous rectifier can be used in the secondary side to further reduce the conduction losses of rectifier diodes. The operating principles of the adopted ZVS forward converter with centre-tapped rectifier are analysed in detail. The design consideration and circuit example of the ZVS forward converter are presented. Finally, experimental results based on a ZVS forward converter with 5 V/16 A output load are provided to verify the effectiveness of the adopted converter compared with the asymmetrical half-bridge converter

Design and implementation of zero-voltage-switching flyback converter with synchronous rectifier

A design consideration and circuit implementation of a zero-voltage-switching (ZVS) flyback converter with synchronous rectifier are presented. To reduce the voltage spike due to the transformer leakage inductance when the main switch is turned off at the flyback converter, one auxiliary switch and one clamp capacitor are used in the adopted converter. The resonant circuit, consisting of leakage inductance and output capacitance of switch, is used to achieve ZVS operation for all switches during the transition between the main switch and the auxiliary switch. The synchronous switch is used on the transformer secondary side to reduce the conduction losses further and to increase the circuit efficiency. The operating principle and system analysis of the adopted converter are discussed in detail. The design example of the adopted power converter is presented. Finally experimental results based on a 5 V/20 A prototype circuit are provided to demonstrate the system performance.

Elucidation of the intrinsic loss arising from switch output capacitance Coss in ultra-high-speed low-loss power converters

Attempts to drive down the switching losses of hard-switched unipolar devices by increasing gate drive current levels are ultimately limited by the device output capacitance, which thus represents an intrinsic loss. The paper presents an in-depth analysis of the charging and discharging of the output capacitance and the associated loss producing mechanisms. It is shown that energy is stored in the depletion layer of the device during turn-off and then dissipated as heat during the turn-on process. The instantaneous power dissipated in the device is thus different to the instantaneous power loss measured at the device terminals, although the total energy loss over one complete turn-off and turn-on cycle is still faithfully reproduced. An analytical approach to determining the intrinsic switching loss due to the output capacitance is presented and verified by experimental results and by TCAD simulation. It is shown that around 20% of the total switching losses arise from the intrinsic output capacitance loss under fast-switched inductive load conditions. A comparison of Si and SiC FET devices demonstrates the potential for SiC power devices to provide an energy efficient option for very high frequency switching.