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Can I use two pulse trains as describe below to fire a set of anti-parallel thyristors? Is there any potential danger in this firing scheme?

PS: I must use pulse train firing in my application.

enter image description here

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  • \$\begingroup\$ Uhm why not simply use a TRIAC ? See en.wikipedia.org/wiki/TRIAC You ask about "danger", what danger? To the environment? Or do you mean "Will it work?" Yes I think it will work provided you apply the pulses for each Thyristor with the correct polarity to that Thyristor. I still think a TRIAC would be easier though, almost everyone would use a TRIAC for this switching AC. Or if you insist on Thyristors. use a bridge rectifier to make DC and switch that. \$\endgroup\$ Commented Nov 3, 2017 at 10:16
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    \$\begingroup\$ By 'danger' I meant 'misfiring' that could damage the thyristors. My application demands the use of thyristors. Cheers. \$\endgroup\$
    – HacLe
    Commented Nov 3, 2017 at 10:24
  • \$\begingroup\$ @bimpelrekkie It is how I handle my own systems -- two scrs rather than a triac. There are downsides using triacs vs this arrangement. But it would be a discussion I'd rather avoid for now, except I'll suggest there is less conflation of options and more management options. Suffice it, it's not always better with triacs. Regardless, this sounds like homework. \$\endgroup\$
    – jonk
    Commented Nov 3, 2017 at 10:31
  • \$\begingroup\$ @HacLe: (1) No you trigger once per half-cycle. (2) The trigger has to be relative to it's cathode so you can't reference the two together. \$\endgroup\$
    – Transistor
    Commented Nov 3, 2017 at 12:47
  • \$\begingroup\$ @Transistor - why not? How about connecting a MOC3020 optotriac like this: i.ytimg.com/vi/miyQHCq3HRs/hqdefault.jpg \$\endgroup\$ Commented Nov 3, 2017 at 15:39

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It is safe to use pulse train triggering. Actually pulse train triggering is the only way to handle inductive loads with thyristors or triacs. There is no danger at all. If you are not using pulse train triggering a DC component could flow in such situations. Very nice explanation about pulse triggering can be found in:
http://www.datelec.fr/secteur/ST%20AN308.pdf

The pulse triggering as indicated in the drawing of OP has a high frequency in respect to the mains frequency and is required in cases of inductive loads triggering failure due to Back EMF from DC motors.

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  • \$\begingroup\$ It isn't by the way. A pulse train is usually used because a pulse transformer is used to provide isolation, a nice simple solution. You can have a continuous gate current for the conduction angle if you design a circuit as such \$\endgroup\$
    – user16222
    Commented Nov 4, 2017 at 9:34
  • \$\begingroup\$ @JonRB. A pulse train is required when you need refire the thyristor or triac within the cycle. The pulse transformer is only for isolation and has nothing to do with requiring a pulse train. \$\endgroup\$
    – Decapod
    Commented Nov 4, 2017 at 20:37
  • \$\begingroup\$ There is a difference between a pulse train at a frequency of the mains (or twice that) and that at say 10kHz. Look at what the OP has drawn \$\endgroup\$
    – user16222
    Commented Nov 4, 2017 at 22:10
  • \$\begingroup\$ @JonRB. See my improved answer. Also read the article in the reference or at least a part of it. \$\endgroup\$
    – Decapod
    Commented Nov 5, 2017 at 14:00

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