I am new to electrical engineering and was trying to design a toggle flip-flop. Will this circuit work? Circuit design

The D2 (LED) should remain on once T1 is pressed and released. T2 should short the power from the transistor and turn it off until T1 is pressed again.

D1 is supposed to keep the base on TRAN1 positive once activated. Is this correct, or will it not happen?

If it won't work, how could I rewire it to function properly?

  • \$\begingroup\$ Nope, it won't happen. \$\endgroup\$ Jan 19, 2017 at 16:06
  • \$\begingroup\$ There are numerous resources online (circuit simulators) that will allow you to play around and see what will work and what won't. You can also download LT Spice (it's free). \$\endgroup\$
    – Tyler
    Jan 19, 2017 at 16:07
  • 1
    \$\begingroup\$ The current came from the base to the emitter dropping a potential of .6 V , why would it go back to base ? \$\endgroup\$
    – Vrisk
    Jan 19, 2017 at 16:25
  • 1
    \$\begingroup\$ Realistically speaking, you need two transistors minimum to make an RS flip flop and either more transistors, or to add a couple capacitors and diodes to make a toggle flip-flop. \$\endgroup\$ Jan 19, 2017 at 16:45

1 Answer 1


Why this circuit doesn't work/can't work as a toggle flip flop.

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Pressing T1 will short Q1 collector-base reducing Q1 to a diode. Current can then flow through R1, base-emitter Q1 and LED D2 causing the LED to light up. D1 is reverse biased and will not conduct.

Release T1, Q1 is off and D2 will extinguish. There is no latching function.

Press T2 and current flows through R1 but nothing else happens.

Press T2 and T1 simultaneously and T2 shorts across Q1 and D2 - nothing happens.

Effectively your circuit is just a battery, resistor, PTM switch and LED in series.

If it won't work, how could I rewire it to function properly?

Start again from scratch and research how BJTs work and how latch circuits work.


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