automatic switch

Discussion in 'General Electronics Chat' started by aj_87, Jan 17, 2013.

  1. aj_87

    Thread Starter New Member

    Jan 16, 2013
    please could you help?
    i need a circuit that will block voltage lower than 5V
    is there a specific component for this or will i need to build a sub-circuit?

    It's a circuit that runs from a dynamo on a push bike.
    Obviously the dynamo will take a second or two to get up to 6+ volts.
    But my circuit only works when the voltage is above 5V because the device doesn't accept it at first you have to plug it in when you’re moving which can be a bit dodgy.
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    Last edited: Jan 17, 2013
  3. codexdj

    New Member

    Jan 16, 2013

    7805 DC regulator might help, it usually gives solid 5V output for greater input voltages from 7 - 20V, i think it will block voltages below 5V. got to try though :) let me know

    happy testing

  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    I've tried it, it doesn't do that. It very sloppily follows the input minus a volt or three till it reaches 5V.
  5. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    Please be more specific. Instead of saying it is a circuit - tell us what the circuit is meant to do. It matters.

    If you want to run 500 LEDs for a custom illumination system or if you want to run a small LCD display readout of an accelerometer/speedometer, those are two different examples we might guess and they would involve different power requirements.

    Battery backup power with an isolation diode from the dynamo is the simplest system.
    It depends on what you need.