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I'm trying to make a circuit that will latch on\off with a pushbutton. This is what I have, but the LED just stays on even though the current shows the latch is working. Thoughts? Thanks :)

Latching Switch

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    \$\begingroup\$ Why do you have a 100Ω resistor in parallel with your LED? \$\endgroup\$ – Majenko Oct 16 '14 at 23:24
  • \$\begingroup\$ Just the way the schematic I pulled some of this from had it set up. \$\endgroup\$ – Dominic Luciano Oct 17 '14 at 1:46
  • \$\begingroup\$ @DominicLuciano what software are you using for those schematics? \$\endgroup\$ – alex gray Dec 8 '15 at 17:04
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A thought:

S1, below, is a SPDT (Form C) momentary pushbutton switch, and you can get rid of all that circuitry with a single chip, like this:

enter image description here

EDIT:

On second thought:

enter image description here

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  • \$\begingroup\$ That neat! Except everything has to be SMD and tiny at that, and I need more of an SPST solution \$\endgroup\$ – Dominic Luciano Oct 17 '14 at 16:19
  • \$\begingroup\$ I can't imagine why you'd think my offering wasn't surface mount and much smaller than yours, but my edit should easily take care of any of those doubts. \$\endgroup\$ – EM Fields Oct 17 '14 at 19:46
  • \$\begingroup\$ No no, I knew yours was smaller, but I'm still learning about how small SMD gets, so sometimes small is still large until I read the datasheet and it's like, "Better get a microscope". Your revision starts with the LED on, and push the button just momentarily turns it off \$\endgroup\$ – Dominic Luciano Oct 17 '14 at 22:01
  • \$\begingroup\$ Not true. My revision starts with the LED either ON or OFF, and pushing the button causes it to change state and stay in that state until the button is pressed again, changing its state, and so on... If you want the LED to start in a known state, then use an RC integrator connected to either SET- or RESET- to get that done. \$\endgroup\$ – EM Fields Nov 17 '14 at 4:01
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You have drain and source swapped on Q4, your output P-channel MOSFET. The body diode is passing current regardless of the state of the gate.

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  • \$\begingroup\$ No such luck when I unswapped it. The LED still stays on \$\endgroup\$ – Dominic Luciano Oct 17 '14 at 1:29
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4093 Latch

This guy seems to work. Thanks guys :)

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