Jae-Kuk Kim

A New Standby Structure Using Multi-Output Full-Bridge Converter Integrating Flyback Converter

This paper presents a new standby structure where the standby flyback converter is integrated with the zero-voltage switching (ZVS) multi-output full bridge DC-DC converter. While the standby power is generated from the conventional flyback converter in standby mode, the auxiliary output of multi-output full-bridge converter is used for the standby output in normal mode. The validity of this proposed structure is confirmed by the experimental results from 12V/58A for DC-DC output and 5V/3.2A for standby output prototype.

A New Standby Structure Based on a Forward Converter Integrated With a Phase-Shift Full-Bridge Converter for Server Power Supplies

This paper presents a new standby structure where a forward converter is integrated with a dc-dc phase-shift full-bridge (PSFB) converter for server power supplies. While a typical standby structure consists of an independent flyback converter, the proposed standby structure is integrated with one leg of the dc-dc PSFB converter. Its main advantages are that the voltage across a standby switch is clamped at the link voltage across the link capacitor and that the standby switch achieves zero-voltage switching over entire load range. The validity of the proposed standby structure is confirmed by the experimental results from 12 V/58 A for the dc-dc output prototype and 11.5 V/1.5 A for the standby output prototype.

On/Off Control of Boost PFC Converters to Improve Light-Load Efficiency in Paralleled Power Supply Units for Servers

This paper proposes an on/off control of boost power factor correction (PFC) converters to improve the light-load efficiency in paralleled power supply units (PSUs) for servers. The proposed scheme operates the PFC stages of two paralleled PSUs alternately during one cycle of a 60-Hz ac input only at light loads. This improves the light-load efficiency without deteriorating the heavy-load efficiency by reducing load-independent losses such as capacitive turn-on and core losses. In addition, the proposed scheme alleviates the harmonic distortion by reducing the discontinuous conduction mode region. Experimental results from 1.6-kW PFC boost converters are shown to verify the proposed work.

A Three-Level Converter With Reduced Filter Size Using Two Transformers and Flying Capacitors

This paper proposes a pulse-width modulation (PWM) three-level converter with reduced filter size using two transformers. The proposed converter has many advantages. All switches sustain only the half of the input voltage and since the secondary rectified voltage is a three-level waveform, the output filter inductor can be reduced. Also, because of the power sharing of transformer and reduced output inductor, high efficiency can be obtained. The operational principle, analysis, and design considerations of the proposed converter are presented in this paper. The validity of this study is confirmed by the experimental results from a prototype with 600W, 500–600V input, and 60V output.

Zero-Voltage Switching Postregulation Scheme for Multioutput Forward Converter With Synchronous Switches

A new multioutput forward converter is proposed. It consists of four synchronous switches in the secondary side for two outputs with the same ground. The primary switches control the main output voltage, and the synchronous switches in the transformer secondary side control the auxiliary output voltage. The main advantages of the proposed converter are that the secondary regulation switch for auxiliary output can achieve the zero-voltage switching at the entire load conditions and the secondary rectified voltage is a three-level waveform, which can reduce the output filter. The operational principle, analysis, and design considerations of the proposed converter are presented in this paper. The validity of this study is confirmed by the experimental results from a dual-output (12 V-18.3 A and 5 V-6 A) prototype for personal computer power supply.

Derivation, Analysis, and Comparison of Nonisolated Single-Switch High Step-up Converters With Low Voltage Stress

This paper presents nonisolated single-switch high step-up converters with low voltage stress. Based on the conventional flyback converter, one single-switch high step-up converter is derived. The voltage stresses on the switch and diodes are limited by using a clamping diode and voltage doubler structure. Also, to further reduce the voltage stresses of them, another single-switch high step-up converter is proposed simply by using one additional capacitor and rearranging the components. Thus, lower voltage-rated switch and diodes can be used, which results in higher efficiency. The operational principle, analysis and design considerations of each converter are presented in this paper. The validity of this study is confirmed by the experimental results from 24 V input and 250 V/125 W output prototype.

Isolated Switch-Mode Current Regulator With Integrated Two Boost LED Drivers

A new isolated switch-mode current regulator is proposed for an LED driving system. The two boost LED drivers are integrated with the dc/dc converter, which results in a simple structure and low component count. The primary side provides an ac voltage source to the secondary side in which one boost inductor, two switches, and diodes comprise two boost drivers. Each secondary switch controls each LED current to be balanced. The voltage stresses of the primary switches are clamped to the input voltage, and those of secondary switches and diodes are clamped to the output voltages. Furthermore, all switches can easily achieve zero-voltage switching by using the transformer magnetizing current without additional auxiliary circuits. The validity of this proposed circuit is confirmed by the experimental results from a 400-V-input and 150-W-output prototype with two 75-W LED strings.

A High-Efficiency PFM Half-Bridge Converter Utilizing a Half-Bridge LLC Converter Under Light Load Conditions

Recently, the various types of the half-bridge (HB) converters with the output inductor have been developed, and they exhibit a good performance in medium power applications such as the server power supplies and personal computer power supplies requiring high output current. However, they have common problems such as the primary and secondary switch turn-off losses and snubber loss in the secondary side caused by the output inductor, which degrades light load efficiency. To relieve these limitations of the conventional HB converters, a new HB converter, which employs one additional switch and capacitor in the secondary side, is proposed for a high efficiency under light load conditions in this paper. Since the proposed converter operates like the HB LLC converter with below operation by turning on additional switch under light load conditions, the switch turn-off losses and snubber loss can be minimized, and the zero-voltage switching (ZVS) capability can be improved. Consequently, the proposed converter can achieve a high efficiency under light load conditions. To confirm the operation, features, and validity of the proposed converter, a 330-400 V input and 12 V/300 W output laboratory prototype is built and tested.

A Novel Accurate Primary-Side Control (PSC) Method for Half-Bridge (HB) LLC Converter

Until now, several researches have been progressed on the primary side control (PSC) methods which decrease the size and cost of the overall system. However, all of them have been applied to the flyback converter, and it is difficult to apply them to the half-bridge (HB) LLC converter due to the large voltage across the secondary leakage inductor of the transformer. In this letter, a new PSC method for the HB LLC converter is proposed to obtain accurate output voltage. In the proposed method, the output voltage is regulated by obtaining the voltage across the primary side of the transformer when the external resonant inductor voltage becomes 0V. At this time, since the voltage across the transformer secondary leakage inductor is small, the proposed method can accurately regulate the output voltage. A 400V input and 20V/85W output laboratory prototype is built and tested to verify the effectiveness of the proposed PSC method.

A novel two-switch active clamp forward converter for high input voltage applications

A novel two-switch active clamp forward converter suitable for high input voltage applications is proposed. It consists of two main switches, one auxiliary switch, one clamping capacitor, and two clamping diodes. The main advantage of the proposed converter, compared to the conventional active forward converters, is that circuit complexity is reduced and the voltage stress of the main switches is effectively clamped to either the input voltage or the clamping capacitor voltage by two clamping diodes without limiting the maximum duty ratio. Also, the clamping circuit does not include additional active switches, so a low cost can be achieved without degrading the efficiency. Therefore, the proposed converter can feature high efficiency and low cost for high input voltage applications. The operational principles, features, and design considerations of the proposed converter are presented in this paper. The validity of this study is confirmed by the experimental results from a prototype with 200 W, 375 V input, and 12 V output.