pentode for alternating current? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: December 27, 2018, 04:59:50 pm
content: So the TRIAC is called the triode for alternating current. Can you have a PENAC or something ?not sure what it would mean even, extra feed back of some sort?there is this thinghttps://en.wikipedia.org/wiki/Quadrac

author: soldar
author_rank: Super Contributor
timestamp: December 27, 2018, 05:05:39 pm
content: Quote from: coppercone2 on December 27, 2018, 04:59:50 pmIt is? Where?

author: coppercone2
author_rank: Super Contributor
timestamp: December 27, 2018, 05:08:23 pm
content: Quote from: soldar on December 27, 2018, 05:05:39 pmgoogle

author: soldar
author_rank: Super Contributor
timestamp: December 27, 2018, 06:15:44 pm
content: Well, it is a triode in the sense that it has three terminals but not in any reference to the tube or valve called triode. It has nothing to do with it or its function. Don't be misled by the name.

author: coppercone2
author_rank: Super Contributor
timestamp: December 27, 2018, 06:18:26 pm
content: maybe they should have called it a ditriac

author: soldar
author_rank: Super Contributor
timestamp: December 27, 2018, 06:25:59 pm
content: Its formal name is bidirectional triode thyristor or bilateral triode thyristor.The name "triode" was coined by British physicist William Eccles sometime around 1920, derived from the Greek τρίοδος, tríodos, from tri- (three) and hodós (road, way), originally meaning the place where three roads meet.The triode tube modulated a current or stream of electrons. The grid voltage modulated the current between cathode and anode. Later a couple more electrodes were introduced for the purpose of changing the electrical characteristics of the device. Hence the name "pentode" which derived from "triode" but the pentode still only really had three main connections: anode, cathode and grid.There is no possible parallel or comparison with the triac that I can think of.

author: In Vacuo Veritas
author_rank: Frequent Contributor
timestamp: December 27, 2018, 07:03:54 pm
content: Quote from: soldar on December 27, 2018, 06:25:59 pmWho cares what you think, Professor? Triac stands for Triode for AC.Go argue with the people who invented the thing:http://bitsavers.trailing-edge.com/components/ge/1972_GE_SCR_Manual_5ed.pdfpage 204Are you also going to argue that "triode mode" for JFET also has no comparison?Sheesh. Kids these days.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 27, 2018, 10:46:54 pm
content: No, we only have N-type electrons. It's notoriously difficult to P-dope vacuum.I've always wanted to try that, make a reasonably high emission, low energy proton generator, and run that through a normal electrode structure. I expect Gm, perveance, transit angle, etc. are all approximately 2000 times worse than an electron tube, alone due to the difference in particle mass.(And you thought GaAs PMOS was bad in comparison to its complement!)In the sense that a device behaves like a tetrode or pentode, but is made of anything: we can cascode transistors just fine, and yes, doing it discrete is as good as doing it monolithic, indeed because we get into trouble if we try making the transistors too close together, which is known as an SCR. Making a bidirectional one would only require the addition of some diodes (to handle breakdown voltage) and connecting another anti-parallel.Tim

author: vk6zgo
author_rank: Super Contributor
timestamp: December 29, 2018, 03:08:58 am
content: Quote from: In Vacuo Veritas on December 27, 2018, 07:03:54 pmInterestingly, bi-junction transistors are three element devices, but their characteristics are more like those of a pentode tube.

author: ArthurDent
author_rank: Super Contributor
timestamp: December 29, 2018, 04:25:54 am
content: A triac can kind of be thought of as two SCRs or thyristors in parallel, one forward and one reversed to work on both halves of an A.C. cycle so a single triode vacuum tube analogy wouldn't work for that reason. Also SCRs are, as the name says, controlled rectifiers (or switches) and the closest vacuum tube analogy would be gas filled thyratrons that have been used since the 1920s. The term "thyristor" was derived from a combination of "thyratron" and "transistor". Since the 1960s thyristors have replaced thyratrons in most low and medium power applications. Once triggered a thyratron or SCR will stay on even with the trigger signal removed and until the voltage across the main terminals drop to essentially zero.https://www.electronics-tutorials.ws/power/thyristor.htmlhttps://en.wikipedia.org/wiki/Thyratron