Recently I want to use a thyristor on my circuit, but I'm not familiar with this. I want to use a Arduino to control the thyristor. So far I don't understand the datasheet of a thyristor characteristic Vgt and Igt.
It shows:
Vgt Max. required DC Gate Voltage to trigger : 1.5 V TJ = 25°C
Igt Max. required DC Gate Current to trigger : 100 mA TJ = 25°C
What I don't understand is "Max". What does this "Max" mean?
Does it mean I can't use the voltage exceed 1.5V? or is it okay to use it exceed 1.5V?
When you are driving your car and you see a sign that says MAX speed is 50mph and you go 60mph. You have now exceeded the MAX and you may pay the price. The MAX voltage on the trigger pin is the same as the speed limit. Yes, you may exceed it, but will probably pay a price. Does that help?
Paul_KD7HB:
When you are driving your car and you see a sign that says MAX speed is 50mph and you go 60mph. You have now exceeded the MAX and you may pay the price. The MAX voltage on the trigger pin is the same as the speed limit. Yes, you may exceed it, but will probably pay a price. Does that help?
Paul
Except you're completely wrong, since "max required" = "minimum to provide for reliable operation".
Note that the max required gate current and voltage go up dramatically with falling temperature, so
you probably want to provide more like 200mA to guarantee triggering over a range of temperatures.
Something like a 22 ohm gate resistor would make sense driven from 5V via a PNP switching transistor
or a p-channel logic-level MOSFET.
Earlier in the datasheet it shows the absolute maximum gate current as 2.5A
So now for the key question: Why use a thyristor, what are you trying to do?
Yes, but it can be confusing! What Perry said is right. It's the maximum required so some devices may, or may not, trigger at 1.2V (or something like that) but all devices of that part number are required to trigger at 1.5V (or more).
And, it is a semiconductor junction so you need to limit the current (typically with a current-limiting resistor) so if you have a higher voltage available the voltage will divide across the resistor and the junction voltage will "fall into place" as long as the resistor is in the right range (just like an LED).
BTW - If you are switching power line AC voltage, the Arduino (and yourself and your computer) MUST BE ISOLATED from the lethal voltages with an optical isolator and there are special opto-isolators for this purpose.
DVDdoug: BTW - If you are switching power line AC voltage, the Arduino (and yourself and your computer) MUST BE ISOLATED from the lethal voltages with an optical isolator and there are special opto-isolators for this purpose.
Totally agree.
Just realised the OP actually posted a link to a data sheet. The specs of that device are huge: 1200-1600V, 1400A. Makes me all the more wonder what project the OP has in mind. That's not your typical AC mains switching device.
Thanks all the answers.
I'm currently trying to build a coilgun. I was trying to use mosfet to control the coil, but I found out to use thyristor is more practical.
Another point I don't understand about the datasheet is that, why there is no "Min" value instead of just the "Max" value. 0 value is under Max value, but you and I all know that it won't turn the thyrisor on. So maybe there should be a minimum value for turning on the thyrisor, but I just don't know how to use it. I was trying to understand the "Gate Characteristics" diagram in the datasheet, but still very confused.
Here is my schematic. There probably has some issue, I just want to know if this schematic is pratical.
johnny2arduino:
Because I was just want to ask about the thyristor, but everyone started to ask about what I wanna do
Yes, of course.
You come asking about a highly unusual type of device, a high power one, where you don't know the basics of... I don't think anyone on this forum wants to be material in you ending up with a Darwin award.
DVDdoug: Yes, but it can be confusing! What Perry said is right. It's the maximum required so some devices may, or may not, trigger at 1.2V (or something like that) but all devices of that part number are required to trigger at 1.5V (or more).
Thanks. TBH I had to read it several times and think about what I expect the parameter to mean before giving my answer. I found it confusing too and would not have been surprised if someone had pointed out I'd got it backwards.
johnny2arduino:
Another point I don't understand about the datasheet is that, why there is no "Min" value instead of just the "Max" value.
What would a minimum value mean? Do you mean a value below which it is guaranteed not to turn on? That's the only thing I can think of that it might mean. I guess no one ever worries about that, so it's not something that's specified. Thyristor drive circuits put no current into the gate when they are not supposed to be turning it on, and some calculated amount of current when they are to be triggered. Between those 2 values no one cares.
