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I have 2 BTW69-1200 thyristor

  • Vrrm = 1200 V
  • Irms = 50 A
  • I tsm (Non repetitive surge peak on-state current) = 610 (8.3 ms) - 580 (10 ms)

Here is the datasheet

https://pdf1.alldatasheet.com/datasheet-pdf/view/93491/STMICROELECTRONICS/BTW69-1200.html

My project needs high current thyristor like 70TPS12 but unfortunately not available in my country.

  • Can I connect two btw69-1200 thyristors togather in parallel to get higher current surge?

How to sum the max Itsm (current surge) after parallel connection?

  • Will the Vrrm decrease in parallel connection?
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  • \$\begingroup\$ Assuming you will manage to turn on both thyristors at the same time, will they share current if one is slightly hotter than the other or will one of them have a thermal runaway? \$\endgroup\$
    – winny
    Commented Oct 16, 2022 at 14:24
  • \$\begingroup\$ ”not available in my country” Digi-Key, Mouser, Farnell, RS and others ship all over the world. Get the right device for the job. \$\endgroup\$
    – winny
    Commented Oct 16, 2022 at 14:26
  • \$\begingroup\$ @winny There are countries that they have trouble shipping to. It's hard to ship anything to Russia or Ukraine right now, for instance. \$\endgroup\$
    – Hearth
    Commented Oct 16, 2022 at 14:40
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    \$\begingroup\$ @Heart Fair point. Allow me to rephrase. Digi-Key, Farnell, Mouser and RS world wide shipping services covers 98 % of the world’s population. If you are lucky enough to be part of it, my recommendation is to get the right device for the job in the first place. \$\endgroup\$
    – winny
    Commented Oct 16, 2022 at 15:36
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    \$\begingroup\$ You generally would not parallel thyristors. It's similar to paralleling BJTs or diodes rather than resistors. They won't want to current share because they are constant voltage drops. The one with the lowest voltage drop will hog all the current. \$\endgroup\$
    – DKNguyen
    Commented Oct 16, 2022 at 18:40

2 Answers 2

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You could add a 50 mV shunt (1 mΩ) in series with each device, to minimize the possibility of unequal current and thermal runaway. At 50 A it will dissipate 2.5 W, while the SCR itself will have a forward voltage drop of at least 1 V or 50 W. This will also allow measurement of current for each device.

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    \$\begingroup\$ I would think this is pretty necessary. Paralleing thyristors is like trying to parallel diodes or BJTs. \$\endgroup\$
    – DKNguyen
    Commented Oct 16, 2022 at 18:40
  • \$\begingroup\$ the shunt is a very good suggestion, I also suggest a snubber circuit in parallel in this case to smooth out the current rise when both turn on, sometimes the rise of the current is uneven having a capacitor can provide extra current while both stabilize.. also derate both thyristors ideally you dont want to run both at their max current capacity \$\endgroup\$
    – Juan
    Commented Oct 17, 2022 at 8:56
  • \$\begingroup\$ @Juan Surely you mean a snubber in series? (Series L || R, or series L with R+C across the device, is a very common application with thyristors. In this case, helping each device to switch on into a little voltage independent of the other, while also sharing current more evenly.) \$\endgroup\$
    – Tim Williams
    Commented Oct 17, 2022 at 12:03
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It will probably work, but you need to ensure that the gate drive is simultaneous and strong for each device so that they trigger simultaneously. If not, then one may turn on before the other and conduct all the load current.

You also need to ensure that both devices are well-coupled thermally. While the data sheet doesn't give sufficient information, it does say the dynamic impedance is 8.5 mΩ. This means that at 32 A (average), the voltage across the device is increased by 8.5m*32 = 0.3 V. This is lower than about 1.2 V, so there is a risk that some thermal unbalancing (thermal runaway) can occur and one device (the hotter one) could conduct the majority of the current.

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