Gabriele Sassone

Lossless current sensing in low-voltage high-current DC/DC modular supplies

New data processing ICs require low-voltage high-current supplies together with high reliability and efficiency. The use of a modular power supply would be the ideal solution, but it requires detecting the current in each module, and resistive shunts are usually used. In this paper, a new lossless current-sensing circuit is presented. This lossless current transducer is obtained by applying the technique used to compensate the parasitic inductance in resistive shunts to the filter inductor of the DC/DC power supply. The causes that can influence transducer response are investigated. The current sensing was implemented in a modular DC/DC power supply and experimental results are reported.

A current-mode power sigma-delta modulator for audio applications

Linear and switching techniques are currently adopted to implement current-mode power stages. Pulsewidth modulation (PWM) is usually employed with the switching technique for both industrial and audio applications. In this paper, the Sigma-Delta modulation is considered as an alternative to the PWM in devising a switching current-mode power stage suitable for audio amplification. The proposed modulator is analyzed and simulated. The whole system was realized on an experimental breadboard. The results carried out on the prototype are reported and discussed. The electrical characterization presents interesting features in terms of linearity, noise, and power efficiency.

High-frequency power transformer model for circuit simulation

A model for the circuit simulation of transformers used in high-frequency power processing is proposed. Many important transformer effects are combined in a single formulation. An Atherton-Jiles model with improved minor-loop handling ability is employed to simulate the hysteresis effect in the magnetic core. Eddy currents and skin and proximity effects are simulated by dynamically approximating the field and flux distributions in the entire structure. Leakage fluxes, capacitive couplings and the influence of temperature on electric and magnetic materials are also included. The parameters needed for simulation are magnetic material characteristics, available in data sheets, core geometry and winding geometry. The model was implemented (built) in the source code of SPICE3.

Study and implementation of a low conduction loss zero-current resonant switch

Zero-current (ZC) resonant switches allow one to reduce the switching losses in high-frequency DC/DC switched mode power supplies. ZC resonant switches can be either unidirectional (half-wave) or bidirectional (full-wave). If a conventional power MOSFET is chosen to implement the ZC resonant switch, the turn-on of the slow intrinsic diode has to be avoided. This is usually done with a fast blocking diode, which is connected in series with the MOSFET. Furthermore, an antiparallel fast diode is added when a FW ZC resonant switch is required. The conduction losses are relevant in this implementation, owing to the threshold voltage and to the series resistances of the two diodes. In this paper, a low-conduction-loss FW ZC resonant switch has been proposed. Its implementation is based on a power MOSFET and a single antiparallel Schottky diode. The possibility of an implementation with a power MOSFET alone is also discussed. A control circuit suitable for the proposed ZC resonant switch has been described. The experimental results obtained from a ZCS-QR buck converter are discussed. >

A high efficiency integrable power converter with soft switching slew-rate control

Slew-rate control (SRC) in integrated switching power stages for noise sensitive systems is presently carried out at switching loss expense by linearly driving the power devices in the active region during the rising and falling output voltage edges. In this work, the zero voltage transition soft switching technique is considered as a means of performing the same SRC function. A bridge-type power scheme is proposed and three structures for the auxiliary branches are evaluated in a breadboard prototype. Experimental results demonstrate that better efficiency than the conventional SRC technique can be attained by splitting the auxiliary branch structure. Finally, preliminary aspects of converter integration are presented.

Single-cycle quasi-resonant converter with controlled timing of the power switches

In this paper, aspects of the real operation of a single-cycle quasi-resonant power converter are analyzed and experimentally verified. In particular, electrical stresses and power losses in the complementary power switches are considered. A variable timing strategy of the switches, based on the direct measurement of the resonance period, is proposed and described. The experimental results and comparisons carried out on a laboratory prototype of the power converter are reported and discussed.

A switching current-mode power stage based on sigma-delta modulation

An integrated current-mode switching power stage for hard-disk drive voice-coil motors is presented. In this system the current in the voice-coil is directly regulated by a sigma-delta modulator. Because of its nature the sigma-delta modulator does not need an external control loop so that a single loop system is obtained. The output stage employs a H-bridge and uses the zero voltage transition commutation technique to control the slope of the output voltage. Output voltage slope control is a basic requirement for the application in order to prevent interference with the hard disk drive signal circuitry. Preliminary experimental results on a prototype are presented.

An integrated switching current-mode sigma-delta power stage for hard disk drives

An integrated current-mode switching power stage for hard-disk drive voice-coil motors is presented. In this system the current in the voice-coil is directly regulated by a sigma-delta modulator. Given its nature, the sigma-delta modulator does not need an external control loop and a single loop system is thereby obtained. The output stage employs an H-bridge and uses the zero voltage transition commutation technique to control the slope of the output voltage. Output voltage slope control is a basic application requirement to prevent interference with the hard disk drives signal circuitry. Preliminary experimental results on a prototype are presented. The system showed it could work with an output slope of up to 500 V//spl mu/s with no significant performance losses.

Novel current transducer in a single-phase active power factor correction system

In line-fed converters implementing power factor correction, the current shaping process requires input current sensing, commonly obtained using dedicated power components as shunts or current transformers. This work presents a current sensing circuit applied to active power factor correction with boost topology, which does not use the previous components. The sensing element is an inductor placed in the input filter, needed to comply with electromagnetic emission standards. The operating principle of the proposed sensing circuit is then extensively discussed, and analytical formulation of the frequency response is given for real conditions. The influence of transducer error on the performance of the power factor correction (PFC) system is also analyzed. Theoretical analysis shows that a system with a low total harmonic distortion (THD) can be achieved, and this is confirmed by experiments on a laboratory prototype.