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In addition to its use as the active device in relaxation oscillators, one of the most important applications of UJTs or PUTs is to trigger thyristors (silicon controlled rectifiers (SCR), TRIACs, etc.). A DC voltage can be used to control a UJT or PUT circuit such that the "on-period" increases with an increase in the DC control voltage.
Graph of PUT characteristic curve, similar to UJT. A programmable unijunction transistor (PUT) is a three-lead electronic semiconductor device which is similar in its characteristics to a unijunction transistor (UJT), except that its behavior can be controlled using external components. In a UJT, the base region is divided into two parts by the ...
A simple SCR circuit with a resistive load. A simple SCR circuit can be illustrated using an AC voltage source connected to a SCR with a resistive load. Without an applied current pulse to the gate of the SCR, the SCR is left in its forward blocking state. This makes the start of conduction of the SCR controllable.
When the delay through the elements is greater than the clock cycle time, the elements are said to be on the critical path. The circuit will not function when the path delay exceeds the clock cycle delay so modifying the circuit to remove the timing failure (and eliminate the critical path) is an important part of the logic design engineer's task.
Both silicon-controlled rectifiers (SCR) and TRIACs are members of the thyristor family. The term thyristor includes all the semiconductor devices, which show inherent ON-OFF behavior, as opposed to allowing gradual changes in conduction. All thyristors are regenerative switching devices, and they cannot operate in linear manner.
low SCR: in case of a short circuit, the current is proportional to SCR, therefore generators with low SCR require less protection and thus are cheaper; low SCR allows shorter air gap and lower excitation field, both decreasing the size (an cost) of the generator; with low SCR the amounts of iron and copper are reduced, lowering the cost; high SCR:
An active circuit used for such a purpose is known as a repeater. In a CMOS integrated circuit, the repeater is often a simple inverter. Reducing the delay of a wire by cutting it in half and inserting a repeater is known as repeater insertion. The cost of this procedure is the additional new delay through the repeater itself, plus power cost ...
Delay calculation is the term used in integrated circuit design for the calculation of the gate delay of a single logic gate and the wires attached to it. By contrast, static timing analysis computes the delays of entire paths, using delay calculation to determine the delay of each gate and wire.