diode and amperage

Discussion in 'General Electronics Chat' started by koka, May 3, 2010.

  1. koka

    Thread Starter New Member

    May 3, 2010
    I do a project that use amperage amplifier that connect to female that exit an electrical thread to split device that have two relays that every relay need 75 watt to turn on electronics devices one of the two relay need to receive a signal of 5 volt
    I use ULN2803 amperage amplifier but the output of this device is opposite in other words if the input is "1" logic the output will be "0" logic with strong amperage
    My question is if this disturb if I connect a high amperage 40mA to turn on the relay that give a signal of 5 volt that I need ?
    The coil have a resistance of 130 ohm and after calculation I receive that the coil need at least 40mA to turn on
    That say that this amperage that depend in the resistant of the coil will give me the 5 volt signal despite of the negative logic ("0" logic) ?
    Other question that I have is what is the different between red and black switching diodes
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    I dont know if I follow you, But if you want to invert the low to a high, a schmitt trigger will do just that.

    Make sure the schmitt trigger you use can handle the current.
  3. mik3

    Senior Member

    Feb 4, 2008
    What you have is an array of transistors. If you want to control relays with them, connect each relay to one of the outputs. Connect one side of the coil to one output of the chip and the other side of the coil to 5V. Apply a 5V signal to the input controlling this output and the relay will work. Also, connect the COM pin of the chip to the 5V supplying the relays.

    Which are the red and which are the black diodes?

    Do they have part numbers?
  4. BMorse

    AAC Fanatic!

    Sep 26, 2009
    I believe the op is asking about IN400x ("Black" Silicon Rectifier) or 1N4148("Red" Glass Sealed Fast Switching Silicon) type diodes...

    B. Morse
  5. eblc1388

    AAC Fanatic!

    Nov 28, 2008
    If this is the case for the OP, then there is no difference in using either a red one or a black one for a 40mA relay coil.

    You can connect either one to the coil as a means of protection against back e.m.f.