Turning relay on with small signal

Discussion in 'Analog & Mixed-Signal Design' started by Blisk, Sep 2, 2016.

  1. Blisk

    Thread Starter New Member

    Jun 6, 2016
    I have this modul for ardurino and I like to use it to protect my power supply against short circuit.
    Problem is because difference is only 185mV on 1 A.
    So how to turn rele on with this module with that low voltage difference?
    If someone have better idea how to turn off power supply when short circuit, please let me know I am looking something small and simple and don't like to use fuses.

    thank you
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Using that module won't be 'small and simple'. Depending on the trip current you want you may have to amplify and offset the module output voltage with an opamp, then use a comparator followed by a driver transistor to control the relay. What do you want to happen once the relay turns on? If you simply use the relay to disconnect the supply from the excessive load then the current will drop to zero and hence the trip circuit will reset and switch the relay off. This will reconnect the load, causing the trip to operate again, and so on, resulting in relay chatter.
    Have you considered a resettable fuse?
  3. Blisk

    Thread Starter New Member

    Jun 6, 2016
    I intent to turn off power from trafo at 3A when short circuit or owerload. But first that must be at lest 2 seconds than relay turn on and cut power from trafo, relay will hold about 5 seconds than turn off.
    For this protection circuit I have separate 12v small switch power supply.
    I am not familiar with resetable fuse, how it works.