Many types of electric equipments are digitized in recent years. However, the configuration of switch mode power supply is still only analog circuit because the analog circuit is held down to low cost. The digitized system is operated on the basis of a processor. When the switch mode power supply is treated as a part of the system, it is difficult that switch mode power supply inhabit alone in the system as the analog-circuit. Therefore, the digitization of the switch mode power supply is necessary to harmonize with other electronic circuits in the system. So far, various examinations have been discussed about digitally controlled switch mode power supplies[1-5]. However, important parameters such as the switching frequency were impractical because the performance of processor was not so good. Recently, due to the development of the semiconductor manufacture technology, the performance of processor such as DSP and FPGA is developed remarkably. Hence, the expectation of the practical realization in the digitally controlled switch mode power supply becomes higher. So far, in many case on digitally controlled switch mode power supply, the control system is constructed by very complicated, difficult modern control theory (nonlinear control theory) such as adaptive control or predictive control. Moreover, also in the most popular and easiest control method such as PID control, the design method is not so clear, and the optimal design is difficult[6, 7]. On the other hand, there are two methods of controller design. One is the digital direct design. The other is the digital redesign. The digital redesign method converts the analog compensator which is designed on s-region into digital compensator. The digital redesign method has some advantages. For example, the control system is designed from classical control theory (linear control theory). Therefore, many experiences and design techniques of the conventional analog compensator can be utilized. Moreover, from the practical stance, the digital redesign method is more realistic than digital direct design. This paper investigates the digitally controlled switch mode power supply by means of classical control theory. Especially, the interesting control technique which is cancelled the transfer function of the converter by using pole-zero-cancellation technique is introduced. This technique is very simple and stability design of converter system is very easy.

Recently, the series resonant converter is widely used for various applications. Moreover, the synchronous rectifier technique has been investigated in low voltage application achieving higher efficiency. The bi-directional series resonant converter can be realized by establishing the synchronous rectifier technique. This paper investigates the ac equivalent model and operating characteristics of bi-directional series resonant converter.

Recently, the performance of the DSP and FPGA is developed remarkably. So, fully digital control is enabled in switch mode power supplies. However, in many cases, the control system is built by very complicatedly and very difficult theories such as the adaptive control. Furthermore, in most popular PID control, its design method of the parameters is not clear, so derivation of the optimal parameters is very difficult. This paper proposes the interesting control technique which is cancelled the transfer function of the converter by using pole-zero-cancellation method. This technique is very simple and easy to stability design.

Recently, the performance of the DSP and FPGA is developed remarkably. So, fully digital control is enabled in switch mode power supplies. However, in many cases, the control system is built by very complicatedly and very difficult theories such as the adaptive control, predictive control, and so on. Furthermore, in most popular PID control, its design method of the parameters is not clear, so derivation of the optimal parameters is very difficult. This paper proposes revolutionary control technique which is cancelled the transfer function of the converter completely by using pole-zero-cancellation method. This technique is very simple and easy to stability design.

Recently, the distributed power system consists of bus converter and POL is usually used for IT infrastructure equipment. The system may become unstable depending on the bus converter design even if each converter has stable operation. Then, the bus voltage is oscillated. Recently, stability problems in distributed power system become series. It is required to overcome these problems as soon as possible. This paper investigates, the improvement of the system stability by the control method. As a result, the full-regulated bus converter is the best as a control method of the bus converter because the full-regulated bus converter can reduce the bus voltage oscillation and correspond to the input voltage variation flexible by the regulation.

This paper presents the fast transient response improvement of two-stage DC-DC converter by using the current feedback control. The two-stage converter consists of a buck converter used as the first-stage and a half-bridge converter used as the second-stage. The proposed control system using the first-stage inductor current and the conventional voltage-feedback control system are analyzed and compared. As a result, it is analytically clarified that the crossover frequency becomes higher by adding the first-stage inductor current in the feedback control loop. The experimental confirmation was obtained with a good agreement, and the effectiveness of the proposed control strategy was verified.

This paper presents the broadband improvement of a two-stage DC-DC converter by using the current control method. The two-stage DC-DC converter consists of a buck converter used as the first-stage and a half-bridge converter used as the second-stage. The proposed control system using the first-stage inductor current and the conventional voltage-feedback control system are analyzed and compared. As a result, it is analytically clarified that the crossover frequency becomes higher by adding the first-stage inductor current in the feedback control loop. The experimental confirmation was obtained with a good agreement, and the effectiveness of the proposed control strategy was verified.

This paper presents the fast transient response improvement of a two-stage DC-DC converter by using the current feedback control. The two-stage converter consists of a buck converter used as the first stage and a half-bridge converter used as the second stage. The proposed control system using the first-stage inductor current and the conventional voltage-feedback control system are analyzed and compared. As a result, it is analytically clarified that the crossover frequency becomes higher by adding the first-stage inductor current in the feedback control loop. The experimental confirmation was obtained with a good agreement, and the effectiveness of the proposed control strategy was verified.

A novel ZVS-PWM controlled current-mode resonant converter previously proposed includes an active-damp circuit and a center-tap type synchronous rectifying circuit. This resonant converter has a high efficiency for a specific input voltage. However, as the input voltage varies from the specific value, the efficiency goes down severely. This paper clarifies the cause of this efficiency drop through the state transition analysis. To overcome the efficiency drop, the authors propose the usage of current-doubler type synchronous rectifying circuits with separate inductors and with a coupled inductor, and examine their steady-state characteristics. Furthermore, the output noise voltage characteristics are measured and compared with the center-tap type rectifying circuit. As a consequence, it is clarified that the proposed rectifying circuits have achieved a high efficiency over 85% for a wide variation of input voltage under the load condition of 3.3 V and 5 A, and that they also have extremely low noise characteristics

The authors have considered the theoretical limitations in the efficiency of DC/DC power converters used in telecommunication applications. The theoretical limitation of efficiency in a single-stage topology and a two-stage topology is compared. As a result, they have selected a two-stage converter consisting of a buck+half bridge topology. This topology is suitable for high output current and low output voltage DC/DC converters. The prototype using a buck+half bridge topology has been made (3.3 V 60 A). The efficiency of the overall converter was 92% at full load, and an ultra high efficiency of 95% at half load was successfully achieved

Many resonant converters have been proposed previously, and their soft-switching techniques have yielded prominent features of high efficiency and low noise. However, the variable-frequency control is normally used to control the output voltage, and it results in a few problems such as the lowest switching frequency limiting the size reduction of the output filter and noise filter, and the beat phenomenon. In order to eliminate these limitations, we had previously proposed a novel ZVS–PWM controlled current-mode resonant converter with an active-clamp circuit. The purpose of this paper is to clarify the steady-state characteristics of this converter. First, the steady-state characteristics are analyzed, and then an analytical expression for the output voltage is derived through the concept of an equivalent ac resistance. Second, the zero-voltage-switching (ZVS) region is clarified. Finally, these analytical results are confirmed by experiment. Thus, it is possible to realize both ZVS operation and PWM control at a constant switching frequency. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 83(1): 59–65, 2000

Steady-state characteristics of the push-pull inverter with a piezoelectric transformer are analyzed. The piezoelectric transformer operating in the 3rd-order longitudinal vibration mode is used in place of a conventional magnetic transformer to produce a high output voltage to light up a cold cathode fluorescent lamp. The circuit operation, the load characteristics, the efficiency and the ZVS conditions are analyzed using equivalent circuits, analytical results are confirmed by experiments. An example of the output current control is also shown

This paper presents the measured results of the output noise voltage and the spectrum of reflected conduction noise of a ZVS PWM series resonant power converter, and compares these noise characteristics with those of the conventional ZVS PWM forward power converter. As a consequence, it is clarified that the ZVS-PWM series resonant power converter achieves extremely low noise characteristics

A Piezoelectric-Transformer (PT) is expected for a low-electric-noise device because it transmits power by mechanical vibration. However, there has been no study about noise of the PT so far. In this paper, we propose a model which focuses on a parasitic impedance of the PT, and compare its simulated result with an observed common-mode noise in the PT DC-DC converter to confirm a mechanism of the common-mode noise occurrence. As a result, we found that the parasitic impedance between the input and output terminals of the PT provides the path for common-mode noise.Furthermore, we propose an improved version of the PT DC-DC converter to reduce the common-mode noise, that is based on this noise analysis. As a result, drastic noise reduction was achieved.

Piezoelectric-transformers (PT) have a lot of merits in comparison with magnetic transformers. We have previously presented some types of piezoelectric-transformer DC-DC converters (PT-converters) for AC-adapters, but their efficiency was restricted. The maximum efficiency was less than 80%. Furthermore, the frequency characteristics of efficiency are not good due to the power loss generated in the input filter circuit of the PT. In this paper the improvement of the converter efficiency by using a different rectifier circuit topology and a synchronous-rectifier technique is described. Furthermore, the frequency characteristics of efficiency are improved by using a different topology of the input filter circuit and its optimum design. As a result, the converter efficiency has been increased up to 88% and the frequency characteristics of the efficiency is also improved.

Steady-state analysis of a ZVS-PWM controlled series resonant converter with active-clamp technique is presented. In this paper, the normal load characteristics and abnormal voltage increase in the case of light load are analyzed. As a result, it is clarified that the stray capacitance of the transformer is a cause of the abnormal voltage increase. Then, it is confirmed that the abnormal voltage increase is suppressed by decreasing the duty ratio. ZVS condition is analyzed and confirmed experimentally. The ZVS is realized in a wide load range. The maximum efficiency of 89% is obtained for the output of 10 V and 2 A.

A multiple-output DC-DC power converter using cross-regulation enables a reduction in size, weight and cost. However, the effect of the smoothing capacitances on the power converter stability has not been discussed enough. Besides, the input circuit is usually required to be isolated from the output side, and the combination of a photo-coupler and a shunt-regulator is often used. However, these components have phase delay and deteriorate the power converter stability. This paper analyzes the stability of three kinds of multiple-output DC-DC power converters using the cross regulation. In the analysis, the transfer function of the photo-coupler and shunt-regulator is estimated from the measured data. Finally, the relationship between the stability boundaries of the power converters and the smoothing capacitances is focused for the size reduction

Operation of the push-pull inverter with a piezoelectric transformer is analyzed. The piezoelectric transformer is used in the third-order longitudinal vibration mode to produce a high output voltage to light up a cold cathode fluorescent lamp. The load characteristics of the inverter are analyzed using an equivalent circuit of the piezoelectric transformer. The ZVS conditions are derived using simplified equivalent circuits to determine the ZVS operation region. These analytical results are confirmed by experiments.

A new piezoelectric transformer (PT) converter which functions as an AC-adapter is proposed. The device's PT operates in longitudinal-vibration mode and features good isolation, incombustibility and compact size. The PT was implemented as a part of the new AC-adapter and a significant reduction in size was achieved as a result. Experimental evaluation of the new adapter confirms that good performance was successfully obtained in spite of the need to comply with strict safety and noise standards.

A novel PWM-controlled resonant converter is proposed. The combination of a resonant converter and an active-clamp circuit makes it possible to control the output voltage of the resonant converter by PWM method. The good controllability and other characteristics of this new resonant converter are analyzed, and are confirmed experimentally