Post by thread:Re: line powered device

At 02:58 PM 09/10/1999 +0200, you wrote: >I'd like to know how much current can be legally drawn from the CO line by a >line-powered device. > >Do you know of any line-powered circuit avaiable in the net ? > >Thank you > >Duilio Foschi > > Maxim has an ap note on this and a special chip for extracting power. It's at http://www.maxim-ic.com Look for the ap note first and get the chip number from that .pdf document. Art

Art, I visited the site but had no luck in finding the part. Do you have the chip number at hand ? Thank you Duilio At 10.26 10/09/99 -0400, you wrote: {Quote hidden}>At 02:58 PM 09/10/1999 +0200, you wrote: >>I'd like to know how much current can be legally drawn from the CO line by a >>line-powered device. >> >>Do you know of any line-powered circuit avaiable in the net ? >> >>Thank you >> >>Duilio Foschi >> >> > >Maxim has an ap note on this and a special chip for extracting power. > >It's at http://www.maxim-ic.com > >Look for the ap note first and get the chip number from that .pdf document. > >Art >

Hi, It seems to me there is no limit to what current you can draw while off-hook except that the current is limited by the CO, 26mA is a minimum available at 6V. On-hook is a different story where the limit is very low, 1uA except while ringing and then ? (numbers from The Art of Electronics, Horowitz & Hill. 60 US$ you'll never regret spending) Jim Hartmann

Yes, the circuit and explanation is shown @ http://209.1.238.246/1st_pages/A1208.htm The chip is a max638 and it looks like 50 ma @ 5v regulated can be drawn from the line when the phone is not in use. Regards, Art At 06:47 PM 09/10/1999 +0200, you wrote: {Quote hidden}>Art, > >I visited the site but had no luck in finding the part. > >Do you have the chip number at hand ? > >Thank you > >Duilio > > >At 10.26 10/09/99 -0400, you wrote: >>At 02:58 PM 09/10/1999 +0200, you wrote: >>>I'd like to know how much current can be legally drawn from the CO line by a {Quote hidden}>>>line-powered device. >>> >>>Do you know of any line-powered circuit avaiable in the net ? >>> >>>Thank you >>> >>>Duilio Foschi >>> >>> >> >>Maxim has an ap note on this and a special chip for extracting power. >> >>It's at http://www.maxim-ic.com >> >>Look for the ap note first and get the chip number from that .pdf document. >> >>Art >> > >

Without even looking at the reference, this sounds wrong. The IC may exist but methinks most Telco's would not let you use it. Assuming this is a switching regulator with 100% efficiency this would require 5ma at 50 volts or an equivalent load resistance of 50/.005 = 10k. This looks like a VERY bad line to any sort of test equipment and would upset Telcos no end. Also, I suspect that this is getting close to the real line seize current in some circumstances and there are circuits which are designed to trip to a high resistance loop and trip eg ringing prior to answering (operator intervention circuitry) so this would run foul of this. Realistically, anything over 1 megohm loop would probably be OK in practice (100K too but test equipment should flag it as a pending fault). 1meg gives you 50 uA or 2500 uwatt. 100% efficiency gives you 500uA at 5 volts. Good enough to run a micro and charge a battery. 100K gives you 10 times as much. Russell McMahon. ========================== {Original Message removed}

Art Allen, KY1K wrote: > Yes, the circuit and explanation is shown @ > http://209.1.238.246/1st_pages/A1208.htm > The chip is a max638 and it looks like 50 ma @ 5v regulated can be > drawn from the line when the phone is not in use. It is made quite clear in the above article that *no* power can be obtained from the telephone line in the "on-hook" state. The circuit's specific purpose is to derive a 5V supply using the SMPS chip, from the line current *while* the device, be it a speakerphone or a modem, is "off-hook". It's just an application note on a 12V to 5V switchmode down- converter. -- Cheers, Paul B.

At 14:58 10/09/99 +0200, you wrote: >I'd like to know how much current can be legally drawn from the CO line by a >line-powered device. > >Do you know of any line-powered circuit avaiable in the net ? > >Thank you > >Duilio Foschi > > This depends on the counrty that the device is going into. Nominally over a 30 minute period the average must be 50uA or less, with short (Very short) spikes of up to 5mA permitted Dennis

> At 14:58 10/09/99 +0200, you wrote: > >I'd like to know how much current can be legally drawn from the CO line by a > >line-powered device. > This depends on the counrty that the device is going into. Nominally over a > 30 minute period the average must be 50uA or less, with short (Very short) > spikes of up to 5mA permitted Off hook, you're only guaranteed 20mA, and at no particular voltage. Typically, you get closer to 50-100mA at 4-12V, but it's a pretty fuzzy number.

At 14:09 10/09/99 -0500, you wrote: >Hi, > >It seems to me there is no limit to what current you can draw while >off-hook except that the current is limited by the CO, 26mA is a minimum >available at 6V. On-hook is a different story where the limit is very low, >1uA except while ringing and then ? > >(numbers from The Art of Electronics, Horowitz & Hill. 60 US$ you'll never >regret spending) > >Jim Hartmann > > These numbers are wrong, or the interpretation is. The amount of current avaliable when off hook is dependant on the SLIC providing the line power. On a PABX the current limites are very different (24V system) to those provided by a CO, also a CO may provide 50V or 100V battery feed. If you have alook you will see that most phones will hold down to around 8V accross the line. The line current at this point can vary greatly! The only thing that you can assume is that 12mA (Nominal minimum value) is requried to keep the phone off hook. The current could be upt to 70mA if you are located cloase to an exchange. While ringing is another story! Dennis

At 17:23 12/09/99 -0500, you wrote: >> At 14:58 10/09/99 +0200, you wrote: >> >I'd like to know how much current can be legally drawn from the CO line >by a >> >line-powered device. > >> This depends on the counrty that the device is going into. Nominally over >a >> 30 minute period the average must be 50uA or less, with short (Very short) >> spikes of up to 5mA permitted > >Off hook, you're only guaranteed 20mA, and at no particular voltage. >Typically, you get closer to 50-100mA at 4-12V, but it's a pretty fuzzy >number. > > There is no guarentee on 20mA being the lower limit, this can be offered over a voltage range from 7.5V to 48V++. Typically exchanges like the System 12 did have off hook detetion down to 8mA, but this is prone to problems. Most counties will accept down to 12mA. AS most lines are well under 4.2kM, the amount of current available at off hook is around 30 tp 50mA. 100mA is not typical as this implies a 200R feed brige, most now have an upper limit of around 72mA. If your phonw will oeprate down to hook voltages of 2.5 to 3V then there is no reason why you can not take more current as possible. You will find that most specs will end at arounf 7.5V accross the terminals, so theroy says that you may take as you wish under this votlage limit (Until the terminal vlotage is passed) But this is not the question it si what can be takne when on hook, and that I have answered Dennis