how to thyristor in series

[DarkZero]

Hey all !

Out of curiosity how would you actually do this in practice i can find some theory but no real world circuit and if one could trigger all thyristor's in series from same trigger circuit


thanks in advance

[T3sl4co1l]

Transformers, or individual gate drivers.

[SeanB]

If all the cathodes are common then you just use a resistor to each gate and drive with over 5V. Otherwise you need a gate drive transformer per unit, and connect all the primary windings in parallel and drive with a high enough current to turn them all on.

If doing in series because of high voltage limits per device the transformers will all need to be rated for operation at the high voltage supply, otherwise you will get flash over. For very high voltage you typically use an optically triggered device, using a fibre optic cable to provide isolation to each device. Driver is typically a few watts of red laser, either HeNe or LED laser, coupled into the fibre bundle.

[DarkZero]

Hey !

Lets say i have light dimmer circuit and lets say i want to use 2 thyristors in series and want to trigger them at the same time how it would be done. because i tried doing it as in the attachment it doesn't work, i think its because trigger signal cant complete circuit of T1. im a bit confused :S

[SeanB]

Why would you want 2 SCR's in series in a dimmer. There you either use a single device and have half wave rectification, or use a TRIAC and have full wave control. If all that you have is a SCR then you use a diode bridge ahead of the whole dimmer so it runs on DC only.

What you have there will not work, as the lower thyristor cannot hold as there is no current flow, while the upper one will never trigger because the lower one will never bring it's cathode voltage down low enough for it to start to turn on.

[DarkZero]

Hey !

i know how a light dimmer works i set this as example im just interested how its done in that case
this article shows it can work with DC http://www.onsemi.com/pub_link/Collateral/AND8030-D.PDF and i used single diode to rectify positive period but it doesnt work

[rs20]

Ask a clear question -- are you trying this on a breadboard and it's not working? Or are you just wondering how the circuit in the article works in theory?

In thoery, when T2 turns on, it effectively connects the cathode of T1 to ground, so it's as if T2 isn't there anymore. So T1 can turn on no problem, especially once T2 has turned on.

If you're trying this on a breadboard and it's not working, post a picture of exactly the schematic you have prepared, and check that your circuit works with a single thyristor to start with, before moving up two two in series.

As others have mentioned, there's absolutely no need or reason to use more than one device with mains electricity.

[DarkZero]

first of all i don't want to make light dimmer / motor control or whatever.

For example:
we have a source of 2000VAC at 50hz but we have for example this thyristor http://ixapps.ixys.com/DataSheet/CS45-16io1.pdf clearly if that's what we have available we would have to connect 2 of those in series so they can handle voltage, so i searched the web for how its done and all i found is trigger them at same time and it should work but no real world circuit on how its done.

Now obviously i don't have 2000VAC source so im doing experiment on what i have 220VAC 50Hz and in the attachment is schematic i used and parts i used with one thyristor it works with 2 in series it doesn't

my question is how to trigger them both at the same time regardless if it can be done with 1 thyristor or triac because i know it can im just exploring this setup!

[T3sl4co1l]

Like I said.  Transformer coupled, or with independent gate drivers.

Tim

[DarkZero]

@T3sl4co1l

ok. so how is independent gate drive done any example circuit ? or is it just 2 of the same circuit connected to its thyristor ?

[onlooker]

How does one balance out the blocking voltage between T1 and T2? The schematics did nothing.

By a matching pair? But, it looks like the leakage current is very sensitive to temperature. I guess this will make the matching harder.

The 2000v/1600V ratio is relatively mild. But, if T1 and T2 turned on at slightly different time, the full 2000V will be applied to one of them momentarily .

[oldway]

To trigger both thyristors, you need a pulse transformer with two secondaries.
Vacuumschmelze seems not to do such transformers anymore, but you can use an IGBT drive transformer instead.
http://www.vacuumschmelze.com/en/products/cores-inductive-components/applications/transformers/drive-transformers/drive-transformers-insulation-voltage-600-vrms-to-2000-vrms.html

Gate pulse requirements for high power scr's :
Open voltage >10V
Short circuit current >1A
Rise time : as fast as possible.
Pulse duration: >10ms

How does one balance out the blocking voltage between T1 and T2?

As with dodes:
Statically by high value resistors in = with each scr.
Dynamically, by low value capacitors in =, but not necessary because you must have an RC snubber to limit dv/dt who make the same function.

The 2000v/1600V ratio is relatively mild. But, if T1 and T2 turned on at slightly different time, the full 2000V will be applied to one of them momentarily

To prevent this, better use the same trigger pulse transformer with two secondaries and a fast rise time trigger pulse.

Scr may be triggered by direct polarity overvoltage without been damaged if di/dt at turn on is low.

Semikron was also making pulse transformers for scr's, I don't know if it is still available or not.

[DarkZero]

besides transformers can it be done with some electronic circuit ?

[bktemp]

Maybe it could be possible using diodes + resistors:
The gate voltage triggers the lower scr. This pulls the upper scr down to almost the same potential and allows triggering of the upper scr.
Your circuit did not work, because both gates are shorted together: This shorts out the upper scr in off state but due to the voltage drop of the lower scr there will not be enough voltage to trigger the upper scr. Therefore diodes are needed to isolate the upper scr in off state and gate resistors to give each scr the full triggering voltage.

[DarkZero]

i think i got it once the lower one triggers it will pull the upper ones gate to gnd "robbing" the current from it. so i just need to share current somehow ill see if diodes work

[oldway]

Why not make your own pulse transformer with a little ferrit toroidal core ?

[DarkZero]

its because i suck with anything Involving coils