A common theme in modern consumer electronics is having a power button that can be tapped to turn the device on, but needs to be held down when it’s time to shut it off. [R. Jayapal] had noticed a circuit design for this setup when using DC and decided to create a version that could handle AC-powered loads.
The circuit relies on a classic optoisolated triac to switch the AC line, although [R. Jayapal] notes that a relay would also work. The switch circuit consists of two transistors, a comparator, a flip flop and a monostable. As you might expect, the button triggers the flip flops to turn the triac on. However, if you hold the switch for more than a few seconds, a capacitor charges and causes the comparator to trip the output flip flop.
The DC circuit that inspired this one is naturally a bit simpler, although we might have been tempted to simply use the output of that circuit to drive a relay or triac. On the other hand, the circuit is set up to allow you to adjust the time delay easily.
Given the collection of parts, though, we wonder if you couldn’t press some 555s into service for this to further reduce the part count. If relays are too old-fashioned for you, you can always use a solid-state relay or make your own.
Ouch. Kind of just begs for a $0.50 microcontroller, no?
Meh depends on your tastes, myself I like soldering more than typing… Difficult to believe with my constant bloviating, I know.
And it would still require something hooked up to the MC that could handle mains AC
i used one with a few extra parts to turn the thing on, control the device with some extra presses and a long press to turn it of. basically i used one pin from the mcu as a hold signal for the power chip, so as soon as the mcu was booted, it took over from the button to hold the ebable pin high. the mcu monitored the button. short presses used for actuons, long press to disable the hold pin.
switching dc or ac is irrelevant as that is just what you hook up to the digitally controlled pin used for the occasion
Not complete; the Vdd (5V) comes from where?
There are dozens (OK. a handful) of Push-On/Push-Off circuits.
My fave : https://breadboardcircuits.com/transistor-push-on-push-off-switch/
Or, one could use a SPDT switch for rock off, rock on functionality. The latch circuit is simpler, and you avoid the annoying ambiguity of not knowing whether your device is booting or shutting down.