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want to know the output voltage of bridge rectifier

Discussion in 'General Electronics Discussion' started by vinod chandran, Jun 29, 2011.

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  1. vinod chandran

    vinod chandran

    Jun 21, 2011
    i have an emergency light circuit that uses power from telephone line. input voltage is 52 volt and it comes to a 4 diode bridge rectifier. positive output of this rectifier goes to LM 317 IC's input. My friend told me that never connect a voltage bigger than 35 to LM 317 IC's input. so i need to know what is the output voltage of bride rectifier in this circuit.
  2. JimW


    Oct 22, 2010
    This is a bad idea on several levels. You didn't say which country you are in, so the following numbers are somewhat arbitrary.

    The 50V you measure is the on-hook voltage. You can't draw more than a few microamps of DC current before the phone company thinks you are trying to make a phone call.

    The line voltage will then be closer to 8V with a loop current of 25ma. The telco will treat your line as in use, and if a call is not placed in a certain amount of time, the line will be temporarily disconnected.

    You have additional problems of handling incoming ring voltages, unintentional answering of incoming phone calls, unbalancing the telco line resulting in bad to horrible hum, and violating a slew of FCC (or equivalent) rules.

  3. vinod chandran

    vinod chandran

    Jun 21, 2011
    hi jim, i'm from india. the phone line here comes with 52v DC. and when it rings 90-120 AC.The designer of this circuit told me that the 6.8K resistor on this circuit never make phone engaged. And when we hook up the phone, the led goes off.
  4. poor mystic

    poor mystic

    Apr 8, 2011
    I did my time as a technician in a telephone exchange and I think that the 6k8 resistor will certainly cause problems with your telephone line.
    I have seen that far higher resistances than 6k8 cause trouble especially with releasing calls that are already up.
    Telephone circuits use very little power indeed, and are an impractical source of emergency lighting power.
  5. vinod chandran

    vinod chandran

    Jun 21, 2011
    thank u dear friend poor mystic for ur advice. and i'm droping this project. but the parts like leds and other things are usefull for an another emergency light that draws power from a battery(6 or 12 V).I am in search of a circuit that doesn't have so many components. I hope you will help me to find a better circuit
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