G. Belverde

Control of the switching transients of IGBT series strings by high-performance drive units

In the field of power electronics, the use of series-connected insulated gate devices, such as insulated gate bipolar transistors or power MOSFETs, is interesting in order to obtain fast and efficient power switches in medium-range power converters. In this kind of application, the control of the voltage sharing across the series strings of devices is an important aspect to be considered. The proposed technique allows obtaining safe commutations of the switches by simple and effective control circuits acting on the gate side of the power devices. In particular, the gate drive units are arranged in order to ensure good performance during the switching transients, while preventing overvoltage peaks on the devices. Both the design criteria and analysis of the control circuit are developed. Several experimental tests are reported in order to demonstrate the validity and correctness of the proposed approach.

Snubberless voltage sharing of series-connected insulated-gate devices by a novel gate control strategy

Insulated gate devices, such as metal oxide semiconductor field effect transistors (MOSFETs) or insulated gate bipolar transistors (IGBTs), are increasingly used in high-voltage power converters where a request for fast power switches is growing. Series connection of devices is a viable approach to manage voltages higher than the blocking voltage of the single device. The main problem in such an application is to guarantee the voltage balance across the devices both in steady-state and during switching transients. In this paper, a novel approach is presented, which is used to equalize the voltage sharing during the switching transients. The main advantages of the proposed method consist in avoiding the traditional use of the snubber capacitors, in the output power side, and in working on the gate side. The application of the proposed gate drive technique is firstly discussed and compared with different solutions, hence, validated by experimental tests applied to the control of series connected devices. Finally, a comparison is performed between the transient behaviors of two different configurations: a single switch with high-voltage blocking capability, and in alternative a series of two devices which together ensure the voltage blocking capability of the single switch. The better performances of the latter configuration, working with the proposed control circuit, over the former have been experimentally demonstrated.

A new gate circuit performing fault protections of IGBTs during short circuit transients

Short circuit faults of IGBTs determine overcurrent through the devices subsequently to a turn-on switching or during the on-state condition, leading respectively to hard switching fault (HSF) or fault under load (FUL). Firstly, the state of the art as appearing in literature is recalled and discussed. A new short-circuit protection scheme, which allows protection of IGBT devices against fault under load and hard switching fault transients, is presented. It performs the fault current limiting action within the short circuit time, and subsequently forces the device to gate on again in a tentative turn-on. Moreover, the proposed circuitry allows strong bounding of the peak of the current in FUL transients. The validity and correctness of the proposed approach has been extensively validated by experimental tests.

A low-voltage MOSFET with small on-resistance: an extended characterization in high-efficiency power converter applications

The paper deals with a new concept applied in designing low-voltage power MOSFETs, which are suitable for high-current low-voltage converter applications, The layout of the proposed device family overcomes the traditional cell structure by a new strip-based geometry. The authors present interesting characteristics due to the advanced design rules typical of VLSI processes and strong reduction of the on state resistance. Further, the technology process allows a significant simplification of the silicon fabrication steps, thus allowing enhancing of the device ruggedness. The high current handling in switching conditions (up to 150 A) with a breakdown voltage in the range between 20-50 V in a convenient package solutions allow to give the correct answers to the low-voltage range switch applications. The paper starts with the description of the main technology issues in comparison with that of standard devices, particularly focusing on the innovations and the improved performances. Moreover a detailed characterization of the MOSFET behavior in traditional test circuit as well as in an actual AC motor drive for wheelchair applications is presented and discussed.

Snubberless balancement of series connected insulated gate devices by a novel gate control strategy

The series connection of insulated gate devices, such as MOSFETs or IGBTs, is increasingly used in high-voltage power converters where the demand for fast power switches is growing. The main problem in such an application is to guarantee the voltage balance across the devices both at steady-state and during switching transients, in order to avoid damaging overvoltages. In this paper, a novel approach is used to balance the voltage during switching transients by controlling the charge profile of the input gate capacitance. The main advantages of the proposed method consist in avoiding the common use of balancing capacitors in the output power side, and in working on the gate drive signals only. The application of the proposed gate drive technique is discussed first and then validated by experimental tests applied to the control of two series connected devices (MOSFETs or IGBTs). The proposed approach is also applicable for more than two devices. In particular, the validity has been proven by computer simulations for three components. Finally, a comparison is performed between the switching behaviors of two different configurations: a high-voltage application having for a high-voltage single switch device; or a series of two lower voltage rated devices. The advantage of the latter configuration, having the proposed active voltage balancing, over the former has been experimentally demonstrated with regard to the turn-off power losses.

Advanced characterization of low-voltage power MOSFETs in synchronous-rectifier buck-converter applications

This paper deals with the performance evaluation of low-voltage power MOSFETs as low side switches in synchronous rectifier buck converter applications. The MOSFET technological structure is based on a strip geometry layout, which allows an excellent trade-off between the on-resistance and the gate charge in comparison with other technologies. The paper starts with the description of the main technology issues focusing on the innovations and the advantages. Furthermore, a new high current device with an optimized gate charge profile is introduced. The switching behavior of the tested devices in DC-DC converter applications (voltage regulator modules) has been experimentally analyzed, in detail, placing attention on the on-state power losses of the low-side switch, on the spurious turn-on phenomenon that can occur during the switching transients, on the gate driving conditions, and on the extension of load current range through the use of multiphase converters. The efficiency of the converter has been evaluated in order to put in prominence the significant improvement obtained by using the new generation of high-current, low-voltage MOSFETs.

Active voltage sharing of series connected strings of IGBT devices in bridge applications

The successful use of series connected strings of MOSFETs or IGBTs, requires equalizing the dynamic and static voltage sharing across the devices. The dynamic voltage imbalance is generally managed via the slope control of the output voltages by snubber capacitors, or by active balancing circuits on the gate side. In this paper, a novel approach, based on the control of the currents supplied to the gates, is proposed. The main issues related to the application in bridge configuration of series connected strings of devices are faced. Firstly, the voltage sensing circuit is analyzed in order to meet the needs of bridge circuits. Experimental tests are performed in order to evaluate the impact of the actual control actions on the devices. Advantages and disadvantages of the proposed active voltage sharing circuit are treated extensively, in order to give also experimental evidence to the switching power losses in comparison with conventional approaches.

Smart power devices in soft switching applications

A smart power device, having a monolithic cascode structure with a high-voltage bipolar junction transistor and a low voltage power MOSFET, is presented and investigated in soft switching applications. The basic characteristics of this device are described both in terms of its structure and electrical performances. In particular, the device behavior is investigated in a zero-voltage quasi-resonant boost converter switching at a frequency of 100 kHz in order to show the high performances of this switch in the field of high voltage, and high-frequency applications. The experimental tests are carried out in several working conditions, and emphasis is given to a comparison with alternative switches as power MOSFETs, and IGBTs in order to understand better the main advantages and drawbacks of this switch. Finally, some figures relative to the power losses versus the switching frequency and the limit on the working frequency of the devices are given with reference to the actual converter used as a benchmark. The experimental results show the superiority of the cascode in the field of the considered switching frequency.

On the series connection of insulated gate power devices

The series connection of insulated gate devices (IGBTs and MOSFETs) is treated with reference to different approaches which ensure a balanced voltage sharing. Both load-side and gate-side techniques are discussed, and their merits and demerits are highlighted. A novel approach, which intervenes during the rise time or fall time of the collector voltages, is discussed and compared to the alternative solutions. Laboratory tests on two IGBT devices are carried out according to the analyzed techniques. Finally, the disadvantages of the multiple connections are discussed in terms of switching speed reduction and power loss increase.

Bipolar-MOS monolithic cascode switch in VIPower technology

In this paper a bipolar-power MOSFET cascode monolithic device, realized in ST-SGS Thomson VIPower (Vertical Intelligent Power) Technology called M3, is presented. The basic device features a three-stage deep-base NPN BJT and a vertical power MOSFET, realized inside the emitter of the trilinton output stage itself for emitter switching. The paper starts with a survey of the main characteristics of the SGS-Thomson Vertical Intelligent Power technology. Then the switching performances of the device are compared to power MOSFET and fast-switching IGBTs in terms of their forward conduction current density turn-off times and breakdown voltages.<<ETX>>