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PWM to DC

Discussion in 'General Electronics Discussion' started by maor, Nov 29, 2015.

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  1. maor

    maor

    8
    0
    Nov 25, 2015
    Hello,
    im trying to convert PWM to DC signal. i succeded to do this with RC low pass filter of R=3.9k and C=30uF, But i want first of all to get the pwm into optocoupler and then convert it to DC signal. when i put the RC low pass filter after the optocoupler i get DC signal but not in the currect value.
    The circuit is attached.

    Thank you,
     

    Attached Files:

    • PWM.pdf
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  2. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    Is the output correct if you measure across R4?
     
  3. maor

    maor

    8
    0
    Nov 25, 2015
    No.
    But if i will remove the rc low pass filter it will be correct. The voltage now on the R4 is pwm but his maximum not reach to 5v.
     
  4. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    You will still need the LPF but the circuit as shown will give an upside down output. Either take the output across R4 with a low pass filter or add a transistor to invert the signal. 47k to base, 1k to 5V, emitter to ground.
     
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