• ETRI Journal
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• v.24 no.3
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• pp.255-258
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• 2002

We created a new design for an Nd-doped clad-pumped silica fiber laser to enhance the pump absorption and lasing efficiency for a butt-coupled, end-pumped scheme. Two concatenated adiabatic tapers formed within the laser cavity simultaneously removed higher order modes and were spliced to conventional single mode fibers. We theoretically analyzed mode propagation along the composite cavity and experimentally achieved continuous wave oscillation in the $LP_{01}$ mode at $1.06\;{\mu}m$ and a laser output power of over 820 mW with a slope efficiency of 27%.

• Journal of the Optical Society of Korea
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• v.5 no.4
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• pp.136-139
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• 2001

We investigated a high-output ower, periodically poled lithium niobate(PPLN) optical parametric oscillator(OPO) pumped by a Q-switched Nd:YAG laser. Given the low optical damage threshold and the limited aperture (0.5mm thick) of PPLN, we tried to maximize the signal output power in a linear cavity consisting of two flat mirrors with a loosely focused pump beam. It is found that this simple cavity structure allowed a robust OPO operation, which was not sensitive to alignment compared with the conventional ones using concave mirrors. A maximum energy of 100$\mu$J/pulse was achieved for the signal at 1.36${\mu}{\textrm}{m}$, while the oscillation threshold was 0.3 mJ/pulse for the pump at 1064 nm.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.1128-1133
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• 2003

A gas driven heat pump (GHP) core design comprises internal combustion engine, compressors incorporated to a cooling/heating system, rubber mountings and belt transmissions. Main excitation farces are generated by an engine, compressors themselves and belt fluctuation. It leads to high vibration level of the mount that can cause damage of GHP elements. Therefore an appropriate design of the mounting system is crucial in terms of reliability and vibration reduction. In this paper oscillation of the engine mount is explored both experimentally and analytically. Experimental analysis of natural frequencies and operational frequency response of the GHP engine mounting system enables to create simplified model for numerical and analytical investigations. It is worked out criteria f3r vibration abatement of the isolated structure. Influence of bracket stiffness between engine and compressors, suspension locations and damper performance is investigated. Ways to reduce excitation forces and improve dynamic performance of the engine-compressor mounting system are considered from these analyses. Implementation of the proposed approach permits to choose appropriate rubber mountings and their location as well as joining elements design A phase matching technique can be employed to control forces from main exciters. It enables to changing vibration response of the structure by control of natural modes contribution. Proposed changes lead to significant vibration reduction and can be easily utilized in engineering practice.

• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.3
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• pp.171-178
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• 2008

Pressure control of hydraulic pump using SRM with pressure predictor and direct torque control method is presented in this paper. Nowadays, high efficiency and high performance motor drive is much interested in hydraulic pump system. But the hydraulic pump system has an inherent defect that its dynamic behavior causes by interaction between the sensor and hydraulic load. It will make low performance of whole system, even unstable and oscillatory. Proposed system integrates pressure predictor and direct instantaneous torque control (DITC). The pressure predictor includes Smith predictor, which is easy to improve unstable or long oscillation in traditional negative feedback control and popular PID control architectures. And DITC method can reduce inherent torque ripple of SRM, and develop smooth torque to load, which can increase stability and improve the torque response of SR drive. So high dynamic performance and stabilization can achieved proposed hydraulic system. At last, the proposed hydraulic system is verified by simulation and experimental results.

• Korean Journal of Optics and Photonics
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• v.9 no.4
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• pp.270-273
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• 1998

We have demonstrated the wavelength tunable ultrashort pulse fiber ring laser proposed the novel method for measuring the cavity loss from relaxation oscillation frequency and the pump power. To suppress the polarization instability the laser cavity is configured with polarization maintaining fibers and to control the center wavelength a 2.4 nm bandwidth tunable wavelength filter was inserted in the cavity. The laser has 8 picosecond pulse width, 10 GHz repetition rate and 1.2 mW average power in 1530-1560 nm operation range.

• Journal of IKEEE
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• v.13 no.4
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• pp.63-68
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• 2009

The power management integrated circuit(PMIC) for CCD image sensor is presented in this study. A CCD image sensor is very sensitive against temperature. The temperature, that is heat, is generally generated by the PMIC with low efficiency. Since the generated heat influences performance of CCD image sensor, it should be minimized by using a PMIC which has a high efficiency. In order to develop the PMIC with high efficiency, the input stage is designed with synchronous type step down DC-DC converter. The operating range of the converter is from 5V to 15V and the converter is controlled using PWM method. The PWM control circuit consists of a saw-tooth generator, a band-gap reference circuit, an error amplifier and a comparator circuit. The saw-tooth generator is designed with 1.2MHz oscillation frequency. The comparator is designed with the two stages OP Amp. And the error amplifier has 40dB DC gain and $77^{\circ}$ phase margin. The output of the step down converter is connected to input stage of the charge pump. The output of the charge pump is connected to input of the LDO which is the output stage of the PMIC. Finally, the PMIC, based on the PWM control circuit and the charge pump and the LDO, has output voltage of 15V, -7.5V, 3.3V and 5V. The PMIC is designed with a 0.35um process.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.15 no.2
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• pp.144-151
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• 2022

In this paper, a 1.5V 256kb eFlash memory IP with low area DC-DC converter is designed for battery application. Therefore, in this paper, 5V NMOS precharging transistor is used instead of cross-coupled 5V NMOS transistor, which is a circuit that precharges the voltage of the pumping node to VIN voltage in the unit charge pump circuit for the design of a low-area DC-DC converter. A 5V cross-coupled PMOS transistor is used as a transistor that transfers the boosted voltage to the VOUT node. In addition, the gate node of the 5V NMOS precharging transistor is made to swing between VIN voltage and VIN+VDD voltage using a boost-clock generator. Furthermore, to swing the clock signal, which is one node of the pumping capacitor, to full VDD during a small ring oscillation period in the multi-stage charge pump circuit, a local inverter is added to each unit charge pump circuit. And when exiting from erase mode and program mode and staying at stand-by state, HV NMOS transistor is used to precharge to VDD voltage instead of using a circuit that precharges the boosted voltage to VDD voltage. Since the proposed circuit is applied to the DC-DC converter circuit, the layout area of the 256kb eFLASH memory IP is reduced by about 6.5% compared to the case of using the conventional DC-DC converter circuit.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.523-526
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• 2001

In this paper, we design and fabricate the high-efficiency and low-power switched-capacitor DC-DC converter. This converter consists of internal oscillator, output driver and output switches. The internal oscillator has 100kHz oscillation frequency and the output switches composed of one pMOS transistor and three nMOS transistors. According to the configuration of two external capacitors, the converter has three functions that are the Inverter, Doubler and Divider. The proposed converter is fabricated through the 0.8$\mu\textrm{m}$ 2-poly, 2-metal CMOS process. The simulation and experimental result for fabricated IC show that the proposed converter has the voltage conversion efficiency of 98% and power efficiency more than 95%.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.512-513
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• 2012

The electric motor is essential to drive turbo machinery. In order to overcome the speed limitations of general motors, the inverter is used to perform high speed to tens of rpm. The high speed drives are widely used in many applications such as turbo blower, turbo centrifugal compressors, and pump using air bearing technique. Starting of high speed motor can cause step out, stall, oscillation of motor because the phase inductance is much smaller than that of ordinary motor. This paper studied on the starting characteristic of variable speed centrifugal chiller considering high speed motor characteristics. Finally, the superiority of the inverter is verified by experimental results.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.413-418
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• 2008

Flow instability in the rocket turbo pump system can be caused by various reasons such as valve, orifice and venturi, etc. The inception of cavitation, especially in the propellant feeding system, is the primary cause of the mass flow and pressure oscillation due to cyclic formation and depletion of cavitation. Meanwhile, the main propellant in liquid rocket engine is the cryogenic one, which is very sensitive to temperature variation, and the variation of propellant properties caused by thermodynamic effect should be accounted for in the flow analysis. The present study focuses on the formation of cryogenic cavitations by adopting IDM model suggested by Shyy and coworkers. Also, the flow instability was investigated in the downstream of orifice by using a developed numerical code. Calculation results show that cryogenic cavitations can lead to flow instability resulting in mass flow fluctuations due to pressure oscillations. And the prediction of cavitations in cryogenic fluid is of vital importance in designing feeding system of LRE.