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Katherine Johnson’s mathematical calculations helped guide some of America’s most important early space missions while she confronted the racial and gender barriers faced by Black women in twentieth-century America.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
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MOS composite static induction thyristor (CSMT or MCS) is a combination of a MOS transistor connected in cascode relation to the SI-thyristor.[1]
The SI thyristor (SITh) unit has a gate to which a source of MOS transistor is connected through a voltage regulation element. The low conduction loss and rugged structure MCS make it more favorable than conversional IGBT transistors.
In the blocking state nearly the complete voltage drops at the SITh. Thus the MOSFET is not exposed to high field stress. For fast switching the MOSFET with only 30–50 V blocking voltage is able. In IGBT, charge carrier concentration at emitter side in n-base layer is low as holes injected from collector easily pass to emitter electrode through p-base layer. Thus the wide-base pnp transistor operates by virtue of its current gain characteristics causing the rise collector-emitter saturation voltage.
In an MCS the positive difference between the voltage of regulation element and conduction voltage drop of MOSFET is applied to location between the collector region and emitter region of the pnp transistor. Hole concentration is accumulated at emitter side in n-base layer because of impossibility of the hole flow through forward bias collector-base junction of the pnp transistor. Carrier distribution in n-base is similar to that of saturation bipolar transistor and low saturation voltage of MCS, even at high voltage ratings, can be achieved.
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MOS composite static induction thyristor (CSMT or MCS) is a combination of a MOS transistor connected in cascode relation to the SI-thyristor. The SI thyristor (SITh) unit has a gate to which a source of MOS transistor is connected through a voltage regulation element. The low conduction loss and rugged structure MCS make it more favorable than conversional IGBT transistors. In the blocking state nearly the complete voltage drops at the SITh. Thus the MOSFET is not exposed to high field stress. For fast switching the MOSFET with only 30–50 V blocking voltage is able. In IGBT, charge carrier concentration at emitter side in n-base layer is low as holes injected from collector easily pass to emitter electrode through p-base layer. Thus the wide-base pnp transistor operates by virtue of its current gain characteristics causing the rise collector-emitter saturation voltage. In an MCS the positive difference between the voltage of regulation element and conduction voltage drop of MOSFET is applied to location between the collector region and emitter region of the pnp transistor. Hole concentration is accumulated at emitter side in n-base layer because of impossibility of the hole flow through forward bias collector-base junction of the pnp transistor. Carrier distribution in n-base is similar to that of saturation bipolar transistor and low saturation voltage of MCS, even at high voltage ratings, can be achieved.
The static induction thyristor (SIT, SITh) is a thyristor with a buried gate structure in which the gate electrodes are placed in n-base region. Since they are normally on-state, gate electrodes must be negatively or anode biased to hold off-state. It has low noise, low distortion, high audio frequency power capability. The turn-on and turn-off times are very short, typically 0.25 microseconds.
An MOS-controlled thyristor (MCT) is a voltage-controlled fully controllable thyristor, controlled by MOSFETs (metal–oxide–semiconductor field-effect transistors). It was invented by V.A.K. Temple in 1984, and was principally similar to the earlier insulated-gate bipolar transistor (IGBT). MCTs are similar in operation to GTO thyristors, but have voltage controlled insulated gates. They have two MOSFETs of opposite conductivity types in their equivalent circuits. One is responsible for turn-on and the other for turn-off. A thyristor with only one MOSFET in its equivalent circuit, which can only be turned on (like normal SCRs), is called an MOS-gated thyristor. Positive voltage on the gate terminal with respect to the cathode turns the thyristor to the on state. Negative voltage on the gate terminal with respect to the anode, which is close to cathode voltage during the on state, turns the thyristor to the off state. MCTs were commercialized only briefly.
The static induction transistor (SIT) is a type of field-effect transistor (FET) capable of high-speed and high-power operation, with low distortion and low noise. It is a vertical structure device with short multichannel. The device was originally known as a VFET, with V being short for vertical. Being a vertical device, the SIT structure offers advantages in obtaining higher breakdown voltages than a conventional FET. For the SIT, the breakdown voltage is not limited by the surface breakdown between gate and drain, allowing it to operate at a very high current and voltage. The SIT has a current-voltage characteristic similar to a vacuum tube triode and it was therefore used in high-end audio products, including power amplifiers from Sony in the second half of the 1970s and Yamaha from 1973-1980. The Sony n-channel SIT had the model number 2SK82 with its p-channel complement named 2SJ28.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Joe Louis.