Please consider the following two circuits:

enter image description here

On the left, is a transistor-latch using a PNP and an NPN transistor. I'd like to replace those two transistors with a thyristor, mainly to get a little more hands-on experience with using thyristors.

So, starting with the left circuit, I tried to replace both transistors with a thyristor and ended up with the circuit on the right. Is my thinking correct?

  • \$\begingroup\$ With the "RESET" switch, I should short directly the anode and cathode of Q5 ... \$\endgroup\$
    – Antonio51
    Commented Aug 17, 2022 at 10:04
  • \$\begingroup\$ More or less. Mind the holding current (R8 is rather large), and you may want some G-K resistance (equivalent to Q2 \$R_{BE}\$) to prevent unintentional turn-on. And as @Antonio51 said. \$\endgroup\$ Commented Aug 17, 2022 at 10:18
  • \$\begingroup\$ I checked the critical dv/dt rise time of the BT169 (Higher if you use 1kOhm between Gate and cathode). See fig 12 of datasheet. ween-semi.com/sites/default/files/2018-11/BT169D.pdf R5 should then be perhaps a little lower. \$\endgroup\$
    – Antonio51
    Commented Aug 17, 2022 at 10:23
  • \$\begingroup\$ Grandpa wants his thyristor back! Next it will be unijunction transistors! Today we have mosfets which make better switches. \$\endgroup\$
    – Kartman
    Commented Aug 17, 2022 at 10:38


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