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Simple Transistor Latch Circuit + Easy Free Circuit Simulator

Simple Transistor Latch Circuit + Easy Free Circuit Simulator



Thanks to all the Patrons for dropping a few bucks in the tip jar to help make these videos happen!
https://www.patreon.com/kdarrah

Quick video here showing you how to build a simple transistor latch circuit using two transistors and a few resistors. Useful for latching polled digital inputs, so you don't 'miss' them in case they're a bit too quick for you. Could also be used as a standalone circuit for alarms, ON/OFF control of circuits, etc... This is a text-book classic circuit - nothing special here, but useful to have in your 'tool-box'.

P-CH MOSFET VP2106:
https://www.digikey.com/product-detail/en/VP2106N3-G/VP2106N3-G-ND/4902414

N-CH MOSFET 2N7000:
https://www.digikey.com/product-detail/en/2N7000TA/2N7000TACT-ND/3042479

The Simulator Here:
http://www.falstad.com/circuit/circuitjs.html

The link to the circuit shown in the...

source

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Tags: transistors

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20 Comments

  1. Date: January 5, 2016 at 10:42
    Author: Maxx B

    Handy circuit to know. That simulator looks excellent for me. I'm just teaching myself electronics, all the other simulators seem very /overly complicated for a newbie. This looks great to learn with.
    Thanks for the video and the introduction to the simulator.

  2. Date: January 5, 2016 at 20:59
    Author: Schlaraffenland

    Does this circuit hold also his state on Poweroff or is it only possible by latching Relays? I'm actually update an older shutdown system and this would be a nice expansion.

    Kind regards

  3. Date: January 14, 2016 at 06:46

    I think your on-line schematic (4:10) is wrongly depicting the right hand FET is N channel when it is a P channel and the reverse for the FET on the left (According to the direction of the arrow in the FET symbol)
    The devices named are correct it's just the symbols are wrong..
    Very nice simulator though….

  4. Date: January 14, 2016 at 14:45

    that's fine but don't you agree the arrows are pointing the wrong way for the channel type they say they are?

  5. Date: January 19, 2016 at 19:11
    Author: Bill Field

    I don't know bout changing my life ??? …. but… this is a GREAT tool. Thanks.

  6. Date: January 25, 2016 at 05:52
    Author: damage.cc

    would it work if you made it such that when you push the button, the micro gets power and runs it's program, then when it is finished, it could pull an output low to effectively kill power to itself?

  7. Date: February 9, 2016 at 17:45
    Author: John Hopkins

    Great demo Kevin! I've been thinking about building a device to transmit a signal to my house when my mailbox is opened, but hit a wall trying to figure out how to turn on the transmitter device only when needed. This is what I need!

  8. Date: February 15, 2016 at 22:31
    Author: Stephen Kramer

    Hi looking for a way to latch on at higher input voltage and latch off at a lower input voltage (so it has hysterisis). Can you recommend any references where I might find a way to make a circuit with this function for hobby purposes ~5-12v, Thanks!

  9. Date: March 20, 2016 at 18:17

    Actually I tried this to switch on and off peripheral devices. But output voltage drops if you pull high current load like 100 mA.
    Then I used an NPN transistor to switch ground line of my device but this had problems too. The device's input voltage is higher than 6V and connected microcotroller's is 5V. Some current leaks out from digital IO lines. So I have been forced to use an electromechanical relay. A Double Pole Double Throw one 🙁

  10. Date: November 3, 2016 at 11:55

    can you please share the circuit that uses 2 transistors and resistors, in the later half of the video you only shared the simulation using mosfet but when i try to replace the mosfet with transistor it doesnot work, i want to switch a low powr circuit using only transistors and 2 switch dont want to use mosfet. So far tried many circuits tried t flipflop too but i am not able to operate the transistor in cut off and saturation
    Hopefully if i cud know the resistor values u used i cud mke it work. Also can you do a video on how to find out the resistance values for operating a latch circuit at different voltages

  11. Date: March 28, 2017 at 15:35
    Author: rene arvizu

    Kevin,
    I am trying to use your circuit to turn off and Arduino by it self, but I am having problems. I am using the BJT on the bottom to turn it off, when I set my output pin HIGH on my Arduino it does not turns off, but when i manually take the wire from the base to a +5v it turns off, but my arduino is not doing it. any ideas on why is not working?

  12. Date: June 22, 2017 at 04:57
    Author: George A.L.

    Kevin eu queria o diagrama esquemático do circuito, você pode mostrar?

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