Is there a simple all in one device that serves as a latching power on/off for use with a momentary switch? I know I can do something with discrete transistors but wondering if there is something now that's in a single package? (with zero current draw when off) -- thanks
and low current also -- 250ma at most.
Sure. A D input FF can have the D input tied to the Q- output and will change state on each toggle on the clock line. You will need to do something to debounce the signal from a momentary switch. That circuit can be more complex than a transistor based On/Off control. Many of the On/Off controls are inherently debounced. You can get a pair of P/N channel FETs in a single package. That's pretty close to a "chip". Add a few passives and you are done.
Ok, here's one that is actually a chip. No passives required. It's not zero power though, just close to it. If it is not allowed to draw any power when off, you will need to make is from mechanical parts. They make push buttons that do this.
A latching reed switch would do the job. They take about a millsecond to switch the reed contact from open to closed, or back again.
It would pay to keep the power on for a bit longer - reeds have a nasty habit of bouncing after they first close - but that's trivial to organise.
Seems to me it would be a credible part these days with momentary switches being so popular? Something in a small case with Vcc in and out, ground and switch input. Crazy price on that Maxim part.
Do they make an on/off latching type in those small keyboard type switches. (I say keyboard for lack of a better term). You know, the small 4 pin types?
Most designs don't need a power supply switch chip. They have an MCU which can implement the same thing, or more accurately, don't ever turn off, because their power is so slow when idle. The CPU senses that the button is pushed, and either puts itself into its lowest power state or actually turns off a pass transistor on the power rail. When the user pushes the button again, it either triggers a "wakeup" input on the MCU, or enables the pass transistor directly.
Not many circuits can't handle a couple of uA drain when "off".
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