Classic Circuits You Should Know - Soft Latching Power Switch
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- เผยแพร่เมื่อ 22 ต.ค. 2023
- Classic Circuits You Should Know - Soft Latching Power Switch
In this CCYSK video we take a look at a simple latching power switch using a 2 input NAND gate and a MOSFET.
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Thanks for squishing the RAMS for us Seahawks fans ! Great tutorial also.
I was hoping you would build the circuit so we could see it in action. I always get confused with explanations without practicle demos. (I always have with everything.)
It's possible to design the switch, so it switches off its own power, meaning the circuit when off is truly off, drawing zero current. This is a boot strap circuit that can be implemented in a number of ways. It relies on the circuit having a known power on state.
Pressing a push button connected to ground, initially provides the power to turn on the P channel enhancement mode MOSFET. A latch, either implemented in software or hardware is then powered, and it takes over the supply to the MOSFET gate. By using a diode or transistor to isolate the gate from the on/off press button, it is possible to continue to sense the state of this switch even when the circuit is powered, as it forms a wired OR with the latch circuit output that drives the gate. So pressing the button again, changes the state of the latch so it no longer powers the MOSFET gate. During this time the circuit is maintained on by the push button being pressed. On releasing the push button, the circuit returns to the truly off state.
While a capacitor can be used to avoid any race condition associated with the latch re-entering the on state while powering down, this can also be addressed using an edge triggered latch,
Where the trailing rising edge of the push button changes the latch state.
The solution is far simpler to understand when a microcontroller is involved, but again the button circuit is similar, driving the gate of a power MOSFET. The push button turns on the supply to the microcontroller, via the gate of the MOSFET, Once running the micro maintains the power on state by using a wired OR with the push button. The micro monitors the button status, if pushed while the micro is running, it removes the signal driving the MOSFET gate, turning the whole circuit off.
Nice video! Thank you
Where is the VCC connected to? I only see a ground in your circuit.
The Vcc pin of the CD4011.
Classics Cool..
Could you do a "classic circuits you should know" that utilise the humble op amp. They have a myriad of uses and are far more versatile than a lot of people realise.
Great video, what's the simplest way to achieve this with the least amount of components?
Thanks Paul. I would have liked an explanation of how the circuit actually works. I guess I am not as advanced as other viewers. Also, I see an OUT, but where is the IN? Maybe my brain is just tired tonight. Take care.
The power and ground are attached to the IC.
@@learnelectronics Thanks Paul. 👍
AND .. NAND 😂
.. corrected at 5:25 ✌️
Dolphins, they lose on porpoise 😂
☮️ brother.
Where is the v+ ?
On the IC