Vratislav Michal

Dynamic duty-cycle limitation of the boost DC/DC converter allowing maximal output power operations

This paper describes the concept of the dynamic duty-cycle limiter of the boost dc-dc converter. Duty-cycle limitation in boost converters is usually used to protect the bottom switch against an excessive current, and also to avoid instability occurring at high duty-cycle operations. Compared to fixed limitation, dynamic limiter enables to detect and maintain maximal possible output voltage VMAX, when desired output voltage cannot be provided e.g. due to excessive load current or increased resistance of the switches. This feature allows to extend the operation range of the converter and powered device. Developed method applies to low power converters, and it is based on the power balance condition detection circuit. This detection is realized via simple and low consumption voltage sensing. Paper presents description of the method, circuit implementation and shows simulated results obtained with integrated 0.13μm CMOS boost dc-dc converter.

Three-Level PWM Floating H-Bridge Sinewave Power Inverter for High-Voltage and High-Efficiency Applications

This paper presents a topology of a single-phase floating full-bridge three-level pulse width modulation (PWM) power inverter suitable for high-voltage/high-power dc-ac conversion. High power efficiency is obtained thanks to the slow (50/60 Hz) biasing of the H-bridge power supply terminals, allowed by a particular arrangement and control of two complementary active neutral point clamped voltage-source converters. As result, the main PWM switching voltage as well as the maximum drain-source voltage VDSS of related transistors are reduced to one-half of the input VDD voltage. This is allowed by the internally generated and accurately balanced middle-node voltage VDD/2. Consequently, advantageous rDS(on) of the low-voltage transistors, along with reduced switching PWM voltage result in considerable decreasing of power losses in whole output power range. This paper introduces the main concept of the floating H-bridge topology, and presents in detail the circuit realization. The performances are demonstrated on 450VDC/230VAC 2 kW power inverter exhibiting 98.6% peak efficiency and realized in very small 100 × 60 × 30 mm3 volume.

Boost DC/DC converter nonlinearity and RHP-zero: Survey of the control-to-output transfer function linearization methods

This invited paper is dedicated to both the nonlinear behavior of a step-up DC/DC converter, and to its linearization. It explains the nonlinear DC and AC control-to-output transfer function and its RHP-zero. The explanation is based on linearized models developed in the paper. These models are suitable for SPICE-like environment, and allow to obtain accurate symbolic equations in Matlab format. The linearization methods based on tri-state PWM and predistortion are also described. The description is followed by a Matlab algorithm allowing fast computation of the voltage-mode PID controller for pre-distorted PWM modulator. As a result, a linearized converter operating in wide duty-cycle range is designed with voltage mode feedback loop.

Switched-Mode Active Decoupling Capacitor Allowing Volume Reduction of the High-Voltage DC Filters

This paper describes active shunt LC decoupling circuit with ceramic capacitors, allowing volume reduction and lifetime improvement of the high-voltage dc filters. Active filtering is based on the energy exchange between high-voltage coupling and low-voltage auxiliary capacitors. The coupling capacitor enables use of the low-voltage switched-mode power stage and low-voltage auxiliary decoupling capacitor. Advantageously, this allows to reduce power dissipation, switching frequency ripple current, and to reduce volume of the circuit. Additionally, power efficiency and capacitor lifetime are improved by using recent high-voltage coupling multilayer ceramic capacitors, reaching very low ESR. This paper provides description of the active decoupling capacitor, and shows an example of the feedback control. Obtained performances are demonstrated on the prototype of 1300-μF/450-V capacitor, allowing to reduce volume by three, when compared to ordinary 450-V electrolytic capacitor.

Time domain CCM/DCM boundary detector with zero static power consumption for integrated high-efficiency step-down DC/DC converters

this paper describes a circuit allowing accurate detection of the continuous (CCM) and discontinuous (DCM) conduction mode boundary. It is suitable namely for very low power integrated DC/DC converters such as the buck or boost. The zero power consumption of this critical block enables to greatly improve the light load power efficiency, and minimize the silicon area. Detection uses a time shift of the power-stage output voltage, which depends on the inductor current value and its polarity. Detector circuit is realized with a digital latch comparator containing only a few digital gates. The paper contains description of the method, example of circuit implementation, and post-layout simulation of integrated detector in 0.13μm CMOS technology, allowing to obtain several mA detection accuracy.

Dual-phase 18V 280μA charge pump with active switches and passive level shifter for low-voltage high-density capacitors

This paper describes the implementation of a high-output current charge pump with passive level shifters, aiming the reliable driving of internal active switches. The technique described here enables advantageous use of high-density integrated Metal-Insulator-Metal (MIM) capacitors with low breakdown voltage, and active switches (MOS transistors). This enables to obtain high power density integration. In addition, capacitor area optimization and feedback control allowing generate constant output voltage are discussed. The 10MHz charge pump was integrated in 0.13μm CMOS process. Thanks to extra epitaxial trench isolation, 18V output voltage with the output current ranging up to 280μA is reached. The target application is the quadrature/frequency compensation of a 3-axis vibratory MEMS Gyroscope.