Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

High voltage switching

  1. Nov 27, 2008 #1
    If I'm using a weak signal like from a tiny magnetic reader, how do I get it to trigger a 120 volt coil?. What electronic hardware do I need to wire in between? Or what type of switch can do this? Thanks.
  2. jcsd
  3. Nov 27, 2008 #2
    What you need is a silicon controlled rectifier, widely available.

    Here's some text from this site: http://www.tpub.com/neets/book7/26c.htm

    The basic purpose of the SCR is to function as a switch that can turn on or off small or large amounts of power. It performs this function with no moving parts that wear out and no points that require replacing. There can be a tremendous power gain in the SCR; in some units a very small triggering current is able to switch several hundred amperes without exceeding its rated abilities. The SCR can often replace much slower and larger mechanical switches.
  4. Nov 28, 2008 #3
    With an SCR, a tiny gate signal controls a much larger anode cathode power which can be connected to your coil....

    What type of output is your magnetic reader providing: just on or off or varying levels of dc output? If the former, an SCR (a switch, on or off) is ok; if the latter, you'll want something like a transistor which has different out levels for different input levels...

    I assume your magnetic reader is basically a dc output...if it's ac, you can make a transformer from two co wound coils....
  5. Nov 29, 2008 #4
    Its just an on/off thing. What I'm trying to do:When a magnet affixed to a rotating shaft passes the reader, it switches the current on. 140 degrees of rotation later I want a second magnet to turn it off. I need a GTO type SCR. Problem is so far is that..... To turn on you send a + tive signal to shut off you send a negative one. How do I get the reader to send the different signals? Any suggestions?
  6. Nov 29, 2008 #5
    You can use solid state relays.. Electronic version of a mechanical relay. Might be slow on-off time though.

    Otherwise IGBT devices.
  7. Dec 1, 2008 #6
    Thanks for you response. It was the perfect solution.
    What I'm trying to do: A trigger magnet affixed to the periphery of a rotating shaft, passes the trigger magnet under a fixed reed switch. It switches a current supply on. 140 degrees of rotation later, I have a second trigger magnet to turn that same current supply off.
    Thanks to your answer, Ive deduced that I actually need a GTO type SCR. Problem now is that..... To turn on(open current flow) you to send a + tive signal and to shut off, you send a negative one. How do I get the one reader to send the two opposite signals? Any suggestions? Also I need to place a protection diode across the coil. There will be the hall effect when I cut the power and there will be reverse EMF on top of that. Can I recapture that enegy and put it into a battery instead of blocking it with the protection diode?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook