Rosario Scollo

A new monolithic emitter-switching bipolar transistor (ESBT) in high-voltage converter applications

In this paper a new family of devices, which is based on a bipolar-MOSFET cascode connection, is presented. The monolithic device is suitable for high-voltage applications. The basic features of this power device, the emitter-switching bipolar transistor (ESBT) component, are described both in terms of physical structure and electrical performances. The field of applications along with the driver requirement is discussed too. The advantages and drawbacks of the presented device in terms of both switching losses and base-gate command circuitry are compared with those of a MOSFET. Finally, the new device is tested by using as a workbench an actual off-line power supply (forward converter), in order to carry out useful information for the power converter designer about the switching behavior and the power losses.

Driving a New Monolithic Cascode Device in a DC–DC Converter Application

In this paper, a case study application of a new device, which is based on a bipolar-MOSFET cascode connection, is presented. The monolithic device can be designed for high-voltage applications up to 1.7-2.2 kV. The basic features of this power device are described in terms of the physical structure and the electrical performance. An application in the field of dc-dc converters is presented, and the drive unit requirements are investigated and discussed through several circuit topologies that are devoted to energizing the four-terminal device. The advantages and the drawbacks of the device are compared with those of a MOSFET in terms of the switching losses and the command circuitry. The correlation between the physical structure of the cascode and its electrical characteristics is explained to better understand some interesting features of the device. Last, the new device is tested by using a forward converter as a workbench to provide converter designers with useful guidelines concerning the switching behavior and the power losses.

Analysis and performances of a new emitter-switching bipolar transistor device suitable for high-voltage applications

This paper deals with the analysis and experimental investigation of a new monolithic cascode, named the emitter-switching bipolar transistor (ESBT), which is suitable for high-voltage medium-frequency applications. The performances of the device are compared with those of a power MOSFET, having equal blocking voltage and equal rated current. The experimental investigation has been carried out in an actual application using a flyback scheme as workbench. The main advantages and drawbacks of the two devices, with special reference to the switching characteristics and the forward voltage, are hence shown, thus providing useful information to the power converter designers looking for a good exploiting of the ESBT. The correlation between the physical structure of the ESBT and its electrical characteristics is explained aiming to understand some interesting features belonging to the device family. Finally, analysis and discussion on the ESBT driving requirements are done, while several circuit topologies, which are devoted to energize the four-terminal device, are proposed.

Series connection of power switches in high input voltage with wide range power supply for gate driving application

In high power systems design an important issue is to provide low voltages, in the range of tens of Volt, tapping from high voltage input line, which is usually in the range between hundreds of Volt to kilovolt, by means of switching power supplies. Low voltages are needed to supply logic control systems and power semiconductors driving the applications. The supply system has to deal, consequently, with both wide input voltage range and electrical insulation. The evaluation of the operative conditions of a driving system for IGCT devices, used in a transmission system application with wide input voltage range, is described. The design of a 100W supply converter is shown considering all the issues related with the series connection of power devices and the needs of insulation. Converter design, modeling and experimental results are shown together with the evaluation of the efficiency of the proposed solution.

A new driving circuit for cascode devices performing optimal control of the storage time

In this paper several driving circuits allowing the optimal feeding of the base of a cascode device are presented. More traditional driving circuits suitable for a cascode device are efficient as long as the collector current is high and quasi constant. However in certain applications such as PFCs. where the collector current changes between zero and higher values, these driving circuits show a considerable drawback, which namely is the over-saturation of the cascode at low values of the collector current. In turn, this means a large charge in the collector and base regions of the cascode that consequently determines an increase of the device storage time. Aiming to face such a problem, a driving circuit that ensures proportional base-voltage has been proposed in order to avoid unsuitable increase of the device storage time. In other words the circuit guarantees an adequate saturation of the cascode in on-state condition and performs an excellent rejection of the voltage supply disturbances along with a high insensitivity to the parametric spreads of the drive components. The new driving circuit that implements a linear control of the base-voltage is suitable for integration.

Impact of the source-path parasitic inductance on the MOSFET commutations

Today, the increase of the power densities requested by electronic applications have brought to a huge diffusion of high-performance power conversion systems that operate in switching-mode (e.g. switching mode power supply or SMPS). The realization of such converters demands for the use of power devices able to carry high density of currents, high blocking voltages, and high switching frequencies. In the meanwhile, since the volume reduction of the power converters asks for the size reduction of the electronic devices (smaller dimensions and increased performances), the impact of the parasitic phenomena starts to become more significant. In this paper, the parasitic effect of the internal source connection between the die and the package of MOSFETs has been analyzed. A demonstration board has been prepared to verify the impact of this parameter on both the commutation times and power losses. A comparison has been made between a conventional MOSFET and an innovative one that allows withdrawing the effect of the parasitic source inductance.

ESBT® power switch in high-power high-voltage converters

Recently available on the market the emitter switched bipolar transistor (ESBT) having high voltage breakdown, low voltage drop, and low switching losses as well, represents an interesting alternative to other power transistors thus giving a new chance to further improve the system efficiency. This paper deals with a new silicon technology used to produce a high voltage monolithic cascode and gives a way to drive the new device in low range power Applications (>lkW). Special focus has been dedicated to inverters and a perspective on the device use in DC/DC converters is given. The loss cutting allows either a strong equipment size reduction or a higher power while maintaining the size.

A forward converter with a monolithic cascode device: Design and experimental investigation

A forward converter for switched mode power supply (SMPS) applications has been designed and realized, with a monolithic cascode device as active switch, looking for the performance enhancement. The operation of this device in a SMPS application is shown in detail, and results regarding electrical and thermal characteristics in comparison to the power MOSFET device solution are discussed. The experimental tests that have been carried out are targeted to show the suitability of this device when a 1000-1500 V operation is required and a single switch topology is the most appropriate. Some remarks about the driving circuit adopted for the cascode are also reported.

Experimental Investigation of Monolithic Cascode Devices in Inverter Leg Applications

In this paper an experimental investigation of the performances of a cascode monolithic device in a half bridge configuration is carried out, and a comparison is performed in the same converter in case IGBT devices are used. The device behavior during the reverse current conduction in the inverter leg is investigated and discussed. The experimental evidence shows that the cascode suffers the same problem of bipolar transistors in inverter leg applications, i.e. the reverse conduction through the base-collector junction as freewheeling diode. Different circuit solutions are analyzed aiming to eliminate this undesired reverse current conduction, and a good topology is appointed.

Optimized Design of Power Semiconductor Devices for DC-AC Royer Converter Topology in Case of CCFL Lighting Applications

The cold cathode fluorescent lamps are particularly used in back lighting of LCD monitors. The supplying circuits must have the characteristic of good thermal management in order to avoid temperature rise over 60 degC, which can cause large dark spots in the screen. In this paper an innovative solution is proposed that consists on a Royer configuration of a current-fed push-pull inverter supplied by a buck DC-DC converter. The main characteristics of this configuration are zero voltage switching operations, which minimize both the power consumption and the thermal dissipation, and the good suitability for system integration, which allows to consider package-targeted economic solutions