Katsuhiko Takigami

2500-V 600-a gate turn-off thyristor (GTO)

GTO self-turn-off capability provides an advantage over an ordinary thyistor, because of forced commutation circuit removal upon inverter and chopper application, thus substantially reducing equipment size, weight, and mechanical noise. A series of high-power GTOs has been developed, with the present 2500-V-600-A unit as its peak. The most essential design problem for this unit is to establish a principle for increasing maximum gate turn-off current (IATO), while keeping overall thyristor characteristics in reasonable balance. High IATOwas attained by decreasing p-base sheet resistance, as well as decreasing n-emitter finger width. Excellent thyristor characteristics were obtained by adopting a low acceptor concentration near the cathode-gate junction. From a device process point of view, introducing a phosphorus redeposition annealing increased carrier lifetime in the p base to a sufficiently high level. This process contributed most strikingly to improving the off-state voltage.

High-frequency 6000 V double-gate GTO's

A double-gate gate turn off (GTO) thyristor, which has an additional gate on the n-base layer, has been proposed to realize high-frequency operation for high-power inverters. The double-gate structure has further been combined with an n-buffer structure to realize narrow n-base width. A forward-blocking voltage of 6000 V was obtained, even at 150 degrees C, when the second gate was shorted to the anode electrode. In order to reduce turn-on and turn-off switching losses, the dependence of these losses on a time interval between two gate triggering pulses has been investigated. It was found that the turn-off loss of approximately 1/20th of that for a conventional GTO thyristor was achieved by adjusting the time interval between the two gate triggering pulses. >

A High Quality Voltage Divider Using Optoelectronics for Impulse Voltage Measurements

By applying an optical measuring system, which consist of light emitting diode, optical fiber light guide and photomultiplier, a high quality shielded resistance divider for impulse voltage measurements, whose response time is less than 5 ns, has been obtained. The characteristics have been verified experimentally.

High Power Gate Turn-Off Thyristors

High power gate turn-off thyristors (GTOs) are studied because of their gate turn-off capability in addition to the usual thyristor characteristics. GTO development, however, has suffered from difficulty in attaining high current gate turn-off capability. From the experimental results, maximum gate turn-off current IATO depends upon a factor (VJ1/ρSPB), as well as the n-base resistivity. On the basis of this principle success was achieved in realizing devices with more than 600 amperes of IATO. Various considerations were made for GTO design, together with numerous experiments in fabrication and characterization.

2500V, 600A gate turn-off thyristor (GTO)

The vital point for 2500V, 600A GTO design is to establish a principle for increasing maximum gate turn-off current (IATO), while keeping overall thyristor characteristics in reasonable balance. High IATOwas attained by decreasing p-base surface resistance to below a certain limit, as well as decreasing n-emitter finger width. Excellent thyristor characteristics were obtained by adopting thick p-base layer with as low as possible acceptor concentration. From a device process point of view, introducing a new annealing process of phosphorus redeposition increased carrier lifetime in the p-base to a sufficiently high level. This process contributed most strikingly to improving the off-state voltage.

Isolation structure optimization for high power reverse conducting GTO

High-power reverse conducting gate-turn-off thyristors (RC-GTOs) enable simpler circuits to be designed. However, GTO and antiparallel diode integration causes turn-off-capability degradation and undesirable GTO triggering by excess carriers flowing from the diode section. An isolation structure that uses a p-base grooving method and a selective lifetime control technique to solve this problem is investigated. A novel isolation structure that contains the drain region is also described. A high-power RC-GTO (4.5 kV, 1000 A) that is based on the optimized isolation structure is presented. The fabrication and electrical characteristics of the device are described.<<ETX>>

Ultra high-speed solid-state circuit breakers for AC and DC power lines

Half cycle solid state circuit breakers, which can cut off fault current in a half cycle, have been put into use. These circuit breakers seem uneconomical because a large number of thyristors are required to be connected in parallel to withstand large fault current. Recently, the authors developed two new economical types of current limiting solid state circuit breakers (CLSCB) for A C three-phase 440 V and DC 750 V industrial power lines. These CLSCBs operate at a fault current limit of 5000 A, AC or DC, where total performance time to circuit interruption is less than 250µsec. This paper deals with the CLSCBs which have fault current interruption and load power control functions.