What is a PUT thyristor?

Answer 1

put (programmable unijunction

transistor)

he Programmable Unijunction Transistor

behaves much like a unijunction transist

or (UJT), but is "programmable" via

external resistors (that is, you can use

two resistors to set a PUT's peak

voltage). Note that the name is a bit of

a misnomer -- as a thyristor, it is a

four layer device, unlike a true unijuncti

on transistor which has but two layers.

Like other thyristors, a PUT looks much

like a junction transistor with a fourth

layer and therefore a total of three P-

N junctions. Meanwhile, a third terminal,

the gate (G), makes a PUT function like

a hybrid of transistor and diode:

PUT symbolPUT cross-section

PUTs are not often used in BEAM;

they're essentially special-purpose

devices in electronics, used for lightingcontrol, motor speed control and othervariable power applications. In combination with an SCR they can, though, makea mean solar engine.

In a pinch, you can build up something

much like a PUT from discrete transist

ors wired as a complementaryfeedback

Here, as soon as any current flows in

either transistor, this current becomes

base current for the other transistor,

and both transistors turn on hard. This

means you can only build up this circuit

using low-leakage transistors ('though

this should be the case with any decent-

quality modern transistor ).