13. SCS Silicon controlled switch
SCS as like as the SCR, is a unilateral, four layer three junction P-N-P- N silicon device with four electrodes namely cathode C, cathode gate G
x
, anode gate G
2
and the anode A. Infact, the SCS is a low power device compared with the SCR. It handles currents in milli amperes rather than
amperes. SCS differs from an SCR in the following aspects. It has an additional gate
—the anode gate.It is physically smaller than SCR.It has smaller leakage and holding currents than SCR.It needs small triggering
signals. It gives more uniform triggering characteristics from sample to sample.
14. PUTProgrammable Unijunction Transistor
PUT is a close relative of the thyristor family. Its has a four layered construction just like the thyristors and have three terminals named anodeA,
cathodeK and gateG again like the thyristors. Yet some authors call it a
programmable UJT just because its characteristics and parameters have much similarity to that of the unijunction transistor. It is called programmable
because the parameters like intrinsic standoff ratio η, peak voltageVp etc can be programmed with the help of two external resistors. In a UJT, the
parameters like Vp, η etc are fixed and we cannot change it. The main
application of programmable UJT are relaxation oscillators , thyristor firing, pulse circuits and timing circuits.
3. Susunan Fisis SCR, Karakteristik dan Fungsi
Untuk membuat tiristor menjadi ON adalah dengan memberi arus triger lapisan P yang dekat dengan katoda. Yaitu dengan membuat kaki gate pada
tiristor PNPN seperti di Gambar 1a. Karena letaknya yang dekat dengan katoda, pin gate dapat juga disebut pin gate katoda cathode gate. Seperti
inilah SCR dibuat dan simbol SCR digambarkan seperti Gambar 1b. SCR dalam banyak literatur disebut Tiristor saja.
Gambar 1. Struktur SCR
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