mosfet Turning a microcontroller on with a flip flop

Posted on Feb 4, 2014

The goal is to be able to turn on and off the load (an 8051 based uC) by pressing both switches. When the uC turns on, it sets PWR high, and then when the switches are pressed again, pin 4 of the flip flop goes low, turning off the boost regulator and uC. The issue that I`ve been having is that in the off setting (pin 4 low), the PWR pin is held a

mosfet Turning a microcontroller on with a flip flop
Click here to download the full size of the above Circuit.

t about half the battery voltage, which prevents me from turning the device on. My best guess is that because the uC no longer has a valid ground reference to the battery (the MOSFET is not conducting), the PWR pin is being held in an indeterminate state because of a small current flow through the uC. Is this correct Why exactly is it bad, and what would be a better way of doing it I was referencing this post when I designed the circuit. Carson Darling Sep 25 `12 at 17:57 Your ground is your reference, and should always and everywhere be the same. If you place a switch in it you have two grounds, and you lose your reliable reference. Solution: high-side switching, before the inductor. stevenvh Sep 25 `12 at 18:01 @stevenvh I think that while they can be answered in the same way, they are different. As I see it, this one is about switching the power to the uC, while the other one is about switching a load from the uC. clabacchio™ Sep 27 `12 at 7:59 If you really want a toggle switch without using the micro, then you need to make the FF operate as a /2 counter where Din is connected to Qbar out rather than V+. Adding a small 0. 01 uF cap to the 500K to gnd will give you 10mS debounce filtering. You can always increase that make that bigger for bigger switch bounce times and/or prevent fast toggling intervals. (whispers. BTW Old English cars had positive grounds, and worked ok, but the reason switched grounds are a bad idea,...

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