get power from phone line

Discussion in 'General Electronics Chat' started by alitex, Aug 30, 2009.

  1. alitex

    Thread Starter Active Member

    Mar 5, 2007
    122
    0
    i use sm8223 as CID detector i want power from phone line to run it,
    i need 4V , 20 mA, is there circuit for that,


    thanks alot
     
  2. Externet

    AAC Fanatic!

    Nov 29, 2005
    758
    57
    Hi.
    First you need a polarity steering circuit which is nothing else than a bridge rectifier connected with the AC terminals to the telco pair.

    The bridge (+) and (-) terminals are ready then to supply the 4 Volts to your circuit just by connecting a 3.9V / 1Watt zener across them. Any telco line must be capable to supply 20mA.

    If you do not want to use the zener in the case most of the current flows trough it, you will have to connect a resistor instead, selecting its value to trim the voltage and current to needs. The resistor may fall in the neighborhood of 120 Ohms.

    ( If the resistor is disconnected while the gadget is in operation, it may get fried from higher voltage presence in the line, up to 50 V; plus the possibility of an incoming ring call with 90VAC )

    The telco line will be seized in that operating conditions and unable to receive a call. After some time, the central office equipment will time-out the dial tone, place a 'hang up' voice message; or go mute; or whatever their policy is for a off-hook line. I do have a microcontroller that communicates data via telco powered by telco.
    I also have a pocket transistor radio that is powered from telco; four or five different strobe lights operating on ringing; A 9V battery charger that works from telco power too. Of course most modern telephones are telco powered too, with bells, whistles, displays, lights and microcontrollers.

    Check the application notes for that chip; it may have sample circuits.
    By the way, I saw caller identification devices at the 99 cent store yesterday.
    Miguel
     
    Last edited: Aug 30, 2009
  3. alitex

    Thread Starter Active Member

    Mar 5, 2007
    122
    0

    thanks alot but there is some questions,
    the first one:is there kinds of Rectifier bridges,
    i have device supplied form telco line, it is 12 leds only(it consume about 30V bec. it connected serial together),i made the same of circuit but not the same of rectifier bridge, unfortunatly it not work.
    the second one: what is most of current what i can git from telco
    thank you
     
  4. Externet

    AAC Fanatic!

    Nov 29, 2005
    758
    57
    Yes, there is hundreds of kinds of rectifier bridges. Here is only a few:
    http://www.c-realevents.demon.co.uk/comprecyc/bridgerec.jpg
    If you did not know about them, it would be better if you do not play with telephone lines until you learn more.

    To turn on a dozen LEDs with the telco line, the sum of their voltage drop if in series should be supplied by the available voltage from the telco; which drops in voltage with the more load you place on the line, and the polarity must be observed. I do not know your meaning of "bec"

    The most current you can get from telco is around 40mA at about 5 Volts, depends on your location.

    Telco lines can, but are not meant to light leds.
    Miguel
     
  5. alitex

    Thread Starter Active Member

    Mar 5, 2007
    122
    0
    it mean: because
    i don't know how i can thank you
    i'm ready to any service
     
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