TRIAC circuits at higher frequency - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: November 04, 2019, 05:36:49 am
content: Is this ever done? When I think of these components I think only of 60Hz power.Are there time constants associated with something like RFish use in traditional circuit topologies? audio power transducer, sonar, etc?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 04, 2019, 05:46:38 am
content: Not much use beyond 400Hz, AFAIK. At some point, dV/dt of the mains itself, or of nuisance transients from other switching activity, will trip a thyristor.Some SCRs can be used for pulsed operation down in the 10us range, turning on. That's about it.Tim

author: coppercone2
author_rank: Super Contributor
timestamp: November 04, 2019, 05:56:31 am
content: Quote from: T3sl4co1l on November 04, 2019, 05:46:38 amhmm, sounds like you would need to analyze silicone to try to find innovative solution, I suppose a physics analysis should prove it obvious?I know the SCR is commonly used for pulsed high energy physics, but I was wondering about power signal level use. It's what all the applied usage graphs for device selection show I know, but I wonder if there is something more. I thought there might be a 'horn' some where, or from the sounds of things a hair (speaking in terms of use graphs).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 04, 2019, 06:02:32 am
content: What?They aren't used for signals either, as the voltage drop is annoying (0.6-1.5V) and there is a minimum hold current, below which you need continuous gate drive (which is to say, it behaves like a regular BJT).Tim

author: coppercone2
author_rank: Super Contributor
timestamp: November 04, 2019, 06:05:19 am
content: Quote from: T3sl4co1l on November 04, 2019, 06:02:32 amI mean to regulate in the same manner as they regulate AC power in simple house hold circuits, in the sense of reciprocating continuous action. For what, I don't know. I just wonder how confined this device is.

author: wraper
author_rank: Unknown
timestamp: November 04, 2019, 06:17:26 am
content: SCR driven horizontal scan (and anode voltage) in soviet TV, ~15.6 kHz. SCR itself is said to be used up to 30 kHz:https://rudatasheet.ru/thyristors/ku221/

author: Ian.M
author_rank: Super Contributor
timestamp: November 04, 2019, 07:02:57 am
content: Thee was also an early Thorn EMI solid state TV chassis (or it my have been a hybrid model with a valve line output stage) that used a SCR in its SMPSU. IIRC that ran as several KHz, and was a right b---er to work on as it would blow up at the drop of a hat if anything damped the resonant current reversal that it needed to be self-commutating.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: November 04, 2019, 07:57:54 am
content: Yes many CRT TVs had thryristors in the horizontal deflection circuit because it was driving the HV xformer as well, these always ran hot and were a PITA.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 04, 2019, 10:27:22 am
content: I can imagine. I've seen induction heaters that used "inverter grade" SCRs (stacks of them, because t_q is better in the lower voltage ratings; they were using 200V SCRs IIRC, small pucks), in 3rd harmonic mode, at 30kHz. So, the inverter ran at 10kHz, which is impressively fast as SCRs go.They didn't come in for service very often (and apparently not just because of their age and presumably small population); apparently they were quite reliable for what they were. Not much tuning range though, I think those machines were only used for heat treating on wire lines (either annealing between drawing dies, or after the last die for heat treating as the case may be).Thing with SCRs in an inverter is, if for any reason it should stop, the whole thing is a fucking bomb. Perhaps there's some merit in providing a redundant commutation circuit, I don't know. Most likely, you'll be replacing semiconductor fuses at least. (Guessing those units came in after failing to clear fuses without further damage.)Tim