Electronic- Electrical mediator

Discussion in 'General Electronics Chat' started by Nathan Hale, Jul 19, 2013.

  1. Nathan Hale

    Thread Starter Active Member

    Oct 28, 2011
    Hello Everyone, hope all is well with everyone.
    I had a question ( for the past 3 months) about Electronic devices that control regular appliances that run on 120 volts. For the sake of simplicity I will use a modern dishwasher as an example.

    What is the device that is in between the "electronics side" of the system and the "electrical side" of the system?
    For example lets take the control panel of the dishwasher shown here. http://www.quietestdishwashers.com/dishwasher-images/GLD4900PBB.JPG

    I am sure the 120 volts that's reaching the motor doesn't and shouldn't go through the whole delicate electronic circuitry before reaching the motor. ( I am thinking that much of a voltage would end up frying the delicate electronic components, micro-controllers etc in seconds.)
    So there should be some "thing" which takes the user input and then process the input and then sends the actual 120 volts and the high number of amps to the motor or what ever.A thing that is a bridge between the electronic and electrical system of the dishwasher.

    What is that device/system/relay or whatever that does this Electronic- Electrical mediator job? I cant imagine the power directly going through the electronic control circuitry !
    I cant imagine that a simple transistor can take a small voltage as an input signal at its base and end up sending 120 volts through the collector emitter region!
    I apologize if I was going around in circles or if i didn't explain my question well but i can re phrase it if you want.

    Thanks a lot for the replies!
  2. wayneh


    Sep 9, 2010
    There are many options. The "brain" and controls usually operate off of a DC supply built into the machine. All or most of the smart functions are processed at low voltages and low current. Very little power is involved.

    When high power is needed, the control signals are used to trigger relays and various semiconductor devices that can also handle large power. SCR, SSR, TRIAC are a few examples. Higher power DC can be switched with a MOSFET, a special transistor.

    Household appliances usually also contain various fuses, thermal fuses, and other safety-related switches that break power to the entire unit if a problem is detected.

    I don't know if this begins to answer your questions.
    Nathan Hale likes this.
  3. Nathan Hale

    Thread Starter Active Member

    Oct 28, 2011
    YES!!!! It is all making sense now! and yes! you are beginning to answer my question. You actually might have answered it in full when you used that word " Trigger Relay " !!
    Thank You very much for the reply.
  4. MaxHeadRoom


    Jul 18, 2013
    The control panel in many appliances uses a Printed circuit board with relays, that cost ~$200 when the $20 relay fails!!:rolleyes:
    As Wayneh intimated, The elements on your stove are usually controlled by a solid state device called a Triac, this is 'burst' fired when turned to an intermediate setting, essentially turning the element on for progressively shorter bursts as you turn it down, this is done to avoid H.F. interference if it were fired with something called phase angle control.
    Now solid state devices such as SCR's and Triacs will switch AC and replace mechanical relays where possible, the common problem with relays is contact failure due to arcing.