Simone Buonomo

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.

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.

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.

ESBT® Power Switch in High Efficiency DC-DC Converter

Well established in low-voltage low- medium- power applications for their high efficiency, DC-DC converters are also widely used in high-voltage high-power Telecom and Industrial applications which are always demanding for higher and higher efficiency. 1200 V State-of-the-Art IGBTs are the best choice in the field of high Current and Three-phase DC-DC converter working at a switching frequency up to about 20 kHz, while 1200 V MOSFETs are definitely the only solution for higher frequency. The trade-off between Conduction Voltage Drop/Losses and switching speed/losses and costs as well helps to make the choice. Recently available in the market, ESBT (Emitter Switched Bipolar Transistor) having high breakdown voltage, low conduction drop and high frequency switching capability, represents the only solution to increase the efficiency and/or reduce the equipment size showing a competitive cost at the same time. A very effective and easy ESBT driving method (ST patent pending) has been fully investigated and tested in a 1.5 kW double switch forward converter. Finally the potentiality of the new device together with the proposed driving solution has been explored in a 12 kW converter.