| Electronics > Beginners |
| Turn on a mosfet at one voltage and off at another voltage? |
| (1/2) > >> |
| gilligan:
Basically, I'm looking to have a mosfet go OFF at say 4v but not go back on till 4.5v to prevent rapid cycling (I know that seems odd but I'm just using it as a switch). So kind of like how a thermostat has a "window" for your temperature. It doesn't just go on and off at exactly 75* it will go on at 76* and off at 74*. Am I explaining myself well enough? |
| tooki:
Yes, it’s clear. The keyword you’re looking for is “hysteresis”. A common implementation of this is the Schmitt trigger. Do a bit of googling for these things and you’ll probably find a circuit that works for you. |
| ataradov:
The thing you are looking for is Schmitt trigger. There are multiple options that may work. The easiest - to use a standard logic gate with a Schmitt trigger input, but you have very little control over threshold voltages. Another option to make your own from a comparator and a few resistors. Here you will define the thresholds. Search for "schmitt trigger comparator" and you will get a ton of circuit diagrams (which are all essentially the same). |
| Wimberleytech:
Here you go. Play with this. I only spent 10 minutes with it, so I am not ready to put it on the space station. You will have to do the math to get your desired trip points. |
| gilligan:
I thought this was the answer I needed (Schmitt Trigger) as it certainly does what I'm asking. Then I realized because I failed to give you guys a complete picture the solution doesn't work. I'm basically looking to power up an arduino from a solar cell withOUT a battery. So, once the panel is putting out enough power, THEN turn it on. Once it drops below a threshold turn it off. The reason for the hysteresis would be so it's not going on and off like crazy when it's just at that threshold... but the problem would be that the reference voltage to the Schmitt Trigger would be going up and down as well ergo not really solving the problem. I've been thinking a Zener Diode (1n4727a ?) in reverse would maybe work to act like a switch? Once it hits 3v it opens up and Bob is your uncle. But all the modeling I've done still shows some current going through below my threshold when it gets close. |
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