Jae-Il Baek

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.

Integrated Asymmetrical Half-Bridge Zeta (AHBZ) Converter for DC/DC Stage of LED Driver With Wide Output Voltage Range and Low Output Current

The conventional half-bridge converter for a dc/dc stage in wide-output-voltage and constant-output-current applications such as LED drivers is limited in achieving high efficiency because it is difficult to be designed optimally. To overcome this limitation, an integrated asymmetrical half-bridge zeta converter is proposed for high efficiency in the overall output voltage range. The proposed converter can be simply implemented by replacing a snubber diode with a switch. The proposed converter operates similar to the asymmetrical half-bridge converter by turning off the switch in the low-output-voltage region, which enables it to have a small dc-offset current in the transformer. In the high-output-voltage region, the proposed converter operates similar to the half-bridge zeta converter by turning on the switch, which has small transformer core loss. Therefore, the proposed converter can achieve high efficiency over the entire output voltage range compared with the conventional converters. The validity of the proposed converter is confirmed by experimental results from a prototype with 400-V input and 90-180-W/3-A output.

A Digital Predictive Peak Current Control for Power Factor Correction With Low-Input Current Distortion

A digital predictive peak current control (PPCC) employing the adaptive slope compensation is proposed in this paper. The PPCC precisely predicts the peak current reference with the adaptive slope compensation according to operation regions and load conditions. Thereby, the PPCC can control the peak inductor current, and it significantly reduces the total harmonic distortion compared to that of the conventional digital average current control with duty ratio feed-forward which is widely used. In addition, parts of the PPCC are implemented by utilizing the internal high-resolution ramp generator and comparator of a digital signal processor without external components. The principle and analysis of the PPCC are presented, and the performance and feasibility are verified by experimental results with universal input (90 Vrms ~ 260 Vrms) and 750 W - 400 V output laboratory prototype.

A Digital Phase Leading Filter Current Compensation (PLFCC) Technique for CCM Boost PFC Converter to Improve PF in High Line Voltage and Light Load Conditions

This paper proposes a digital phase leading filter current compensation (PLFCC) technique for a continuous conduction mode boost power factor correction to improve PF in high line voltage and light load conditions. The proposed technique provides a corrected average inductor current reference and utilizes an enhanced duty ratio feed-forward technique which can cancel the adverse effect of the phase leading currents caused by filter capacitors. Moreover, the proposed PLFCC technique also provides the switching dead-zone in nature so the switching loss can be reduced. Therefore, the proposed PLFCC can significantly improve power quality and can achieve a high efficiency in high line voltage and light load conditions. The principle and analysis of the proposed PLFCC are presented, and performance and feasibility are verified by experimental results from the universal input (90-260 VAC) and 750 W-400 V output laboratory prototype.

Battery Impedance Analysis Considering DC Component in Sinusoidal Ripple-Current Charging

Sinusoidal ripple-current (SRC) charging is a new charging technique that the sinusoidal current superposed with the direct current (dc) charges the battery at the frequency where the battery-alternating current (ac)-impedance reaches a minimum. However, in analyzing the effect on the SRC charging, the dc component of the SRC has not been considered until now. This paper presents a battery impedance analysis when the dc component is considered in the SRC charging. The real battery impedance is analyzed by using an electrical second-order RC battery model and overpotential voltage waveforms. The result shows that the real battery impedance is not minimized at the minimum-ac-impedance frequency. Due to this, in comparison with the constant current (CC)-constant voltage (CV) charging, the charging time, charging amount, and charging efficiency of the SRC-CV charging are not significantly different from those of the CC-CV charging. Rather, due to the ac component, the SRC-CV charging deteriorates the RMS current and maximum rising temperature by 22.5% and 18%, respectively. Also, this paper presents that the CC-CV charging using a slightly larger dc is more suitable for practical applications, since its current stress, charging time, and maximum rising temperature are improved by 2%, 9.7%, and 8.5%, respectively, in comparison with the SRC-CV charging.

Resonant Capacitor O n/ O ff Control of Half-Bridge LLC Converter for High-Efficiency Server Power Supply

In this paper, a simple control method of the half-bridge (HB) LLC converter with one additional switch and capacitor in the primary side is proposed for wide-input-voltage applications with the hold-up time conditions. At nominal input, since the proposed method enables the HB LLC converter to operate with large transformer magnetizing inductance, it can reduce the conduction and switch turn-off losses in the primary side, which makes it highly efficient. On the other hand, during the hold-up time, since the proposed method increases the resonant capacitance by turning on one additional switch, the HB LLC converter can obtain high-voltage gain. To confirm the validity of the HB LLC converter with the proposed method, a 325-385 V input and 56 V/350 W output laboratory prototype is built and tested.

A high efficiency half-bridge LLC converter with simple hold-up compensation circuit

The half-bridge (HB) LLC converter has been widely used in medium power applications because of low component count, no transformer dc-offset current, and wide zero-voltage-switching (ZVS) range. However, the HB LLC converter should be designed with small transformer magnetizing inductance to obtain high voltage gain in wide-input-voltage applications with the hold-up time conditions. It causes the HB LLC converter to have large conduction and switch turn-off losses in the primary side at nominal input where a high efficiency is required. To overcome these problems, a simple control method of the HB LLC converter with one additional switch and capacitor in the primary side is proposed in this letter. At nominal input, since the proposed method enables the HB LLC converter to operate with large transformer magnetizing inductance, it can reduce the conduction and switch turn-off losses in the primary side, which makes a high efficiency. On the other hand, during the hold-up time, since the proposed method increases the resonant capacitance by turning on one additional switch, the HB LLC converter can obtain high voltage gain. To confirm the validity of the HB LLC converter with the proposed method, a 325-385V input and 56V/350W output laboratory prototype is built and tested.

A new efficient hold-up time compensation method for high efficiency DC/DC stage

The conventional two-stage structured power-supply units (PSUs) requiring the hold-up time operation have generally low efficiency dc/dc stage because it is difficult to be designed optimally. As a result, to improve the efficiency of the dc/dc stage, many hold-up time compensation methods have been presented. However, they cannot still optimize the dc/dc stage due to its bad influence on the design conditions. In addition, they can only be employed in certain dc/dc topologies as well as they still ill-affect the design conditions of the dc/dc stage. Therefore, in this paper, a new hold-up time compensation method is proposed to overcome the conventional limitation. Compared to the conventional method, since the proposed method delivers the output power by using not the dc/dc stage but the power factor correction (PFC) stage during the hold-up time, it can optimize the dc/dc stage at the nominal state without any bad influence, which enables the dc/dc stage achieve a high efficiency. Furthermore, it can be widely applied to various dc/dc stages. The validity of the proposed method is confirmed by experimental results from a prototype with 90-264Vrms input and 480W/10A output.

Novel multi-coil resonator design for wireless power transfer through reinforced concrete structure with rebar array

The wireless power transfer (WPT) has many advantages such as convenience of energy transfer and high reliability of system. Therefore, WPT system is widely applied to IT devices, electric vehicle, and industrial application by using concrete structure. However, when is applied to reinforced concrete structure, there is a severe problem that it has very low efficiency for power transfer, which results in high power loss due to interference of the internal rebar array. In other words, although the conventional WPT system has high efficiency under air condition, it has low transfer efficiency under reinforced concrete structure with rebar array. To overcome this problem, this paper proposes a new multi-coil resonator design. It uses main one coil and intermediate 4 coils. The main coil boosts coupling coefficient and the intermediate 4 coils boost self-inductance and a few coupling coefficients. As a result, high coupling coefficient leads to high WPT efficiency. Moreover, the proposed resonator design enables intermediate 4 coils to avoid interference of the rebar array. Therefore, the proposed new multi-coil resonator design for WPT system has high efficiency under reinforced concrete structure with rebar array. To confirm the operation, features, and validity of the proposed resonator designs, a laboratory WPT system with 3.3V/10W is built and tested.

Improved three switch-active clamp forward converter with low switching loss

The improved three switch-active clamp forward (3S-ACF) converter is proposed in this paper. The proposed converter has minimized switching loss on all switches of 3S-ACF converter by simple change of gate control scheme without any additional components. In addition, current stress of clamp diode can be significantly reduced. Though, all switches of the proposed converter have low voltage stress similarly to those of conventional 3S-ACF converter. Therefore, the proposed converter can be the most attractive candidate for high efficiency power supply in wide input applications.