Use the first commercial value above.
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Measurements
Resistor
Capacitor
Transistor
Transformer
Potentiometer
Diode
TRIAC
UJT
LED
FET
SCR
(Silicon-Controlled Rectifier)
SCR or Silicon Controlled Diode is one of the most important components in applications of power load control of high values from electrical grid. Working as a switch electronically triggered, it easily exceeds its mechanical equivalent, for its speed, sensibility and capacity of working in high voltage and current. There is no limit for the number of practical applications it can be used, which is important for all of us know a little about its operation principle, its limitations and main applications.
SCRs can work as trigger elements of electronics circuits, as solid-state relays, high power oscillators, power controls in AC circuits, inverters circuits and many applications which other semiconductors as bipolar transistors, field-effect transistors and common diodes cannot be used.
SCRs have a structure that manifests electrical properties that allows they be used in all of this applications. So, initially we can say that what differentiate a SCR of other common components as diodes and transistors is its structure which gives it well-defined properties.
Summing up, SCR can be understood as a diode that just conducts after the shot and just stop conducting after cutting the anode current.
Animation
Unijunction
Transistor
Unijunction transistors (UJT) are semiconductor devices whose symbol and structure are shown in the picture.
These components have a negative resistance feature that makes it ideal to relaxation oscillators operations, with basic configuration.
Unijunction transistors (UJT) aren’t easily found in practical applications anymore.
TRIAC, from triode for alternating current, is an electronic component equivalent to two thyristors (SCRs) connected in antiparallel with their gates connected together. TRIACs differ from SCRs in that they allow current flow in both directions, whereas an SCR can only conduct current in a single direction. TRIACs are subset of thyristors.
A TRIAC can be triggered by an alternating current applied in the gate. Once triggered, TRIACs continue to conduct, even if the gate current ceases, until the main current drops below a certain level called the holding current. TRIACs' bidirectionality makes them convenient switches for alternating-current (AC).
In addition, applying a trigger at a controlled phase angle of the AC in the main circuit allows control of the average current flowing into a load (phase control).
Low-power TRIACs are used in many applications such as light dimmers, speed controls for electric fans and other electric motors.
When used to control reactive (inductive or capacitive) loads, care must be taken to ensure that the TRIAC turns off correctly at the end of each half-cycle of the AC in the main circuit. For higher-powered, more-demanding loads, two SCRs in inverse parallel may be used instead of one TRIAC. Because each SCR will have an entire half-cycle of reverse polarity voltage applied to it, turn-off of the SCRs is assured, no matter what the character of the load.
Variable Capacitor