I have made the following circuit from a few online sources, it is very basic but uses two NPN transistors to make a latching circuit that toggles when either push button goes to ground.

My Falstad Circuit

NPN Latching

My question is, how would I make this work if I wanted both latches to be triggered when going high instead of low.

Would I need to use PNP transistors instead?

  • \$\begingroup\$ Can you please share an openable link, or better just add a screenshot of your circuit and maybe explain what you are trying to do and where you have problems? \$\endgroup\$ Commented Apr 23, 2019 at 8:51
  • \$\begingroup\$ Hi Niteesh, I tried to use a short URL but stackexchange didn't like it here it is anyway: tinyurl.com/y2bwnt97. \$\endgroup\$ Commented Apr 23, 2019 at 8:54
  • \$\begingroup\$ We don't like short URLs - or, indeed, any URLs, really. They have a habit of disappearing and leaving broken and useless questions and answers. \$\endgroup\$
    – Finbarr
    Commented Apr 23, 2019 at 9:46

1 Answer 1


No, you can just use the same basic circuit but swap the buttons around and add a couple of extra resistors.

This has the arguably slight advantage that the button turns the transistor it's attached to on instead of off, making it a little easier to understand.

But historically, circuits would tend to use active low inputs and connect the switches to ground, especially when using TTL devices which work that way.

Or, as you say, use PNP transistors and flip the circuit vertically.


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Amazing! Updated Falstad Circuit. Would a PNP design use less resistors? \$\endgroup\$ Commented Apr 23, 2019 at 9:54
  • \$\begingroup\$ Yes, it would just be a mirror image of the original circuit. \$\endgroup\$
    – Finbarr
    Commented Apr 23, 2019 at 11:16

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