Detect AC Power supply

Discussion in 'Power Electronics' started by steve_venkat, Nov 8, 2018.

  1. steve_venkat

    steve_venkat

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    This is the circuit I' using to detect the AC voltage.I can't get any output from this circuit..
    Is simply in Idle.Their is no negative voltage is detected.
     

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    steve_venkat, Nov 8, 2018
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  2. steve_venkat

    Alec_t

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    You can't get a negative voltage out, since the '814 output transistor is only connected to a +5V supply.
    What AC voltage are you trying to detect? 110V mains?
     
    Alec_t, Nov 8, 2018
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  3. steve_venkat

    kellys_eye

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    With 100k resistors I'm surprised you're getting anything at all. This means only 0.5mA through the opto's LEDs. Without referring to the data sheet (coz I can't be bothered to download one) is <1mA sufficient to activate the LEDs?
     
    kellys_eye, Nov 8, 2018
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  4. steve_venkat

    steve_venkat

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    Its connected to MCU input,The resistor is connected as pull-up resistor...
    Have to detect 230VAC,But the voltage will vary from 160VAC to 280VAC...
     
    Last edited: Nov 9, 2018
    steve_venkat, Nov 9, 2018
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  5. steve_venkat

    steve_venkat

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    Its 5mA current required.?If the voltage is constant(230VAC) means 4.k OHM is enough for it..?
    But the voltage will vary from 160VAC to 280VAC...
    At this point how to choose the resistor value..?
     
    steve_venkat, Nov 9, 2018
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  6. steve_venkat

    kellys_eye

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    The current range for LED operation can vary considerably yet still allow it to work. Take the average AC voltage (220V) and use that to calculate the required resistor for 5mA current flow. Any changes either side of that will be acceptable.

    Alternatively take the 230V as the 'working value' and choose a resistor for that.
     
    kellys_eye, Nov 9, 2018
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  7. steve_venkat

    Bluejets

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    Bluejets, Nov 9, 2018
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  8. steve_venkat

    steve_venkat

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    The
    The LED in optocoupler is 20mA current and 70mW power dissipate.So I calculate resistor value for 5 different range of input supply and took average value from that.Its 11.1K,2W...Is this Correct method or have to change something..?
     
    steve_venkat, Nov 10, 2018
    #8
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