I need a T flip-flop for 24V. The purpose is to take a 24V 50% duty cycle 0.5Hz pulse wave and halve its frequency to 0.25Hz, so that the output wave toggles between 0 and 24V at the input's rising edge.

I know one solution is to use an impulse latch relay, but those are quite large and expensive.

Since logic circuits for 24V are uncommon, relays or transistors would be most suitable.

There is one solution demonstrated by CreativE EngineerinG (link) which I have replicated in falstad simulator (link), but the simulation does not work properly. I'm unsure about this solution because the simulation does not work and because I need to purchase the components before constructing the circuit, so I must be sure that it works. Plus, this solution is for 5V and not 24V, so the components values must be different, and higher power BJTs will have different internal characteristics.

What is the best solution (preferably one that can be simulated)?

  • \$\begingroup\$ Search "bistable multivibrator circuit" and make a 24V one. \$\endgroup\$ Sep 28, 2020 at 15:23
  • \$\begingroup\$ @BrianDrummond But that will not toggle without the help of some 24V gates! \$\endgroup\$
    – AJN
    Sep 28, 2020 at 15:57
  • \$\begingroup\$ @AJN What gates? 2 transistors and you're done. And if you need a few gates. adapt RTL or DTL circuits to 24V. \$\endgroup\$ Sep 28, 2020 at 16:19
  • \$\begingroup\$ "Best" calls for an opinion. In my opinion the way to do this with the least number of packages on the board is to regulate down to 5V, use a 74HC74 or other suitable flip-flop, then level-shift the output to 24V with a couple of transistors. You'll use less board area and have more reliable operation out of the chute than if you tried to roll your own logic at 24V. \$\endgroup\$
    – TimWescott
    Sep 28, 2020 at 16:24
  • \$\begingroup\$ For comparison, here's what looks like a more robust RTL circuit. seventransistorlabs.com/tmoranwms/Elec_Flipflop.html. \$\endgroup\$
    – TimWescott
    Sep 28, 2020 at 16:27

1 Answer 1


Thyristor T Flip- Flop. It can be made for any voltage and can be controlled with a lower voltage. Through the capacitor (1u) the switching on one thyristor switches off the other.



In principle, there could be only one problem with it if the two thyristors ignite at the same time at the first moment. In practice, this has never occurred due to manufacturing tolerance. It can also be prevented with minimal asymmetry of (gate) parts. It works for sure for 10 pieces, a long time ago I built a decade counter from them. :)

For simulation give C1 a starting voltage of 3-4V (asymmetry) and it will work afterwards.


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