Switching a high voltage with a lower voltage

Discussion in 'The Projects Forum' started by Oarc, Mar 29, 2012.

  1. Oarc

    Thread Starter New Member

    Mar 29, 2012
    Hello everyone,

    This is my first time posting on these forums! I have done my research although I don't know why this was so hard to find out. There were a lot of answers similar to what I was trying to do but were not exactly what I need. I don't really have another few hours to spend searching for a good solution so I am kindly requesting your help for my simple problem :)

    I'm working on a project in which I need to switch a sensor on/off using an MSP430. The MSP430 I am using (MSP430F2003) outputs a max of ~2.6 volts when it's on. The sensor requires a 5 (+/- 0.5) V to operate. My power supply is a stack of AA batteries which totals to ~9V. I have a voltage regulator which takes the 9V and outputs 5V.

    I was initially planning to use an NFET between the 5V voltage regulator and my sensor. However, the NFET drops the voltage by more than .5V, closer to 1V... I then realized I was incorrectly using the NFET and that it probably won't be able to do what I need...

    I attached a simple circuit showing where the switch needs to be, but it needs to be controlled by a 2.6V signal somehow. Since this is for a low power application, fewer components and low quiescent consumption would be great. The image includes the part numbers I have, and I left the NFET off to the side because I don't think there is a way to solve my problem with JUST the NFET.

    Even if you could just point me to the answer somewhere else, I would appreciate it. Thanks in advance! Also let me know if my question wasn't clear enough and I'll try to better explain it.
  2. MrChips


    Oct 2, 2009
    Use an opto-isolator driving a PNP pass transistor.
  3. Oarc

    Thread Starter New Member

    Mar 29, 2012
    Thanks for the idea! I'll look into it!

    Meanwhile, I also got help from a professor who works at 9pm :)

    I'll post back here with my final design in week or so. Thanks for the quick response!