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Thyristor turn on/off time?

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grizedale

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A thyristor after receiving a gate pulse , will turn on within 100ns / 500ns / 2us ? ...which one ?

A thyristor cannot be turned off by any kind of gate pulse or absence of gate pulse, but is only turned off when the current in the thyristor decays below the "Holding current"................

...even then, if the decay below the holding current level lasts for only 100us, then if the current suddenly rises back up above the " latching current" level , then the thyristor will stay conducting.?


Is these maXims truthful?....
 
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WimRFP

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For general purpose thyristors for 50 Hz, 230V mains and up to some kW, I would think of tgt 0.5...2us and tq can be in the 100us range (depending on die temperature and reapplied dV/dt). You may know that there are two "toff" phenomena. The first one is the reverse recovery time like in a normal diode (trr). The other one is because of the recombination of the carriers in the gate region. Even when the current through the thyristor was zero, reapplying anode-drain voltage too soon, may fire the thyristor when there is still sufficient change in the gate (tq).

Normally the thyristor has plenty of time to get rid of all charge (at least a half cycle for 50/60 Hz operation). Other important things are dI/dt just after triggering and maximum dV/dt to avoid uncontrolled triggering.
 

grizedale

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thanks,

will a thyristor tend to switch slower than a sidac?

taking these examples

thyristor: (BT168GW)
**broken link removed**

K1100y Sidac
https://www.littelfuse.com/data/en/Data_Sheets/Littelfuse_Thyristor_Kxxxzy.pdf



...The sidac seems to have a 150A/us rate of rise of current compared to the thyristors 50A/us........................so the sidac would be better for xenon tube triggering.

Does the thyristor's rate of rise of on state current depend on the gate current level.....?
-i ask because the datasheet specifies 10mA of gate current.
-we only have 1mA of gate current in out application so i wonder what "rate of rise of current we will get?

- - - Updated - - -
 
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WimRFP

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Hello,

The current rate of rise should be limited by the circuit. So when dI/dt is circuit limited to 10A/us, you can use both sidac and thyristor.

With your 1mA gate trigger current, I think 15A/us is safe as the datasheets notes:

"Although not recommended, off-state voltages up to 800 V may be applied without damage, but the thyristor may switch to the on-state.
The rate of rise of current should not exceed 15 A/us" And this is a really worst case situation, as you start from zero gate triggering current (instead of your 1 mA).

If you really need high dI/dt, can't you use a small storage capacitor to hold some charge to provide a current pulse? Besides the capacitor you need just some resistors and a transistor.
 

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