Monthly Archives: May 2015

Soft Latching Power Switch

The Raspberry Pi ON/OFF Power Controller that I looked at from Mosaic Industries, Inc. does a good job at 5 VDC but I need the circuit to be able to switch LiPo batteries which have a voltage range of between 2.7 and 4.35 VDC between discharged and fully charged. I looked for dual MOSFET devices which could operate in this range and found the following.

Both of these devices function at these lower voltages however I have been having some oscillation issues with these. When the button is held down to turn off the load, which is a LED, the output is switched off but it turns back on after a few seconds. I have not been able to investigate why this is happening. I suspect that I miswired something but I need to take some time to check.

The International Rectifier device seems to behave a bit better so it may be the one I use but I will need to investigate what the issue is and resolve that before I can move on. I can’t wait to wrap this project up.

If you have an idea as to what my problem may be, please leave a comment to let me know.

UPDATE – 16 May 2015

I determined the reason for the odd behavior was that the N-Channel MOSFET’s gate was floating. I was able to fix this by using a pull-down resistor of 100KΩ. Looking at the schematic, I connected the resistor between Pin 7 and ground. This pulls the gate to ground through the 330KΩ and 1KΩ resistors.