how to make 5volt power from phone lines

[nikhilele]

What is the theory and methods involved in making a 5v power supply from a phone line.

 

[IanP]

You can't get much power of a telephone line, so, if you are happy with ≈200mW you can use this circuit as a good starting point .. see picture below ..
More info at:
**broken link removed**
Instead of the MAX638 you can consider other switching voltage regulators ..

Regards,
IanP

 

[sinip]

What is the theory and methods involved in making a 5v power supply from a phone line.

As IanP already said, you can't get much power from it, and your phone company might also get unhappy about it and disconnect you from the network. But that depends from one phone company to another.

 

[nikhilele]

i am not taking much power, i need power only to run my ckt which is similar to caller id ckt, i have a dtmf decoder and a microcontroller at89c2051, and three leds. thats all.

 

[newelltech]

In the US, phone lines are tested on a regular basis for leakage and disconnected by the phone company if too high. They don't want to pay for power that isn't used for phone service. To them it means a shorted phone line and extra cost.

If you are building your project for your own hobby use, you're probably ok taking a few mA. And if your phone gets turned off, you can just disconnect your circuit for a while.

If you want to sell a commercial product in the US, you will need to have a certified interface that meets their requirements - one of which is low leakage.

Added after 9 minutes:

My reply above is assuming an on-hook condition (ie - phone not in use). So it applies if you need to run your circuit waiting for a call - which you probably do with caller id.

Once the line is off-hook (in use), the phone co. doesn't really care how much current you try to draw. You can even short the line and the current will be limited to something like 50 mA (approx).

The circuit from IanP will work just fine once you are off-hook. However it won't work if the line is on-hook as it will draw too much current and make the line look like it went off-hook. Typically an off-hook condition draws about 20 mA and has about 12 volts.

 

[nikhilele]

i got link from maximum

**broken link removed**

Draw 150mW Of Isolated Power From Off-Hook Phone Line

The circuit from IanP will work just fine once you are off-hook. However it won't work if the line is on-hook as it will draw too much current and make the line look like it went off-hook. Typically an off-hook condition draws about 20 mA and has about 12 volts.

can you suggest me similars ckt without transformer. i have less space.

Added after 1 hours 21 minutes:

or how to obtain such transformer.

Added after 43 minutes:

i got similar topic on edaboard


This topic has confused me

flatulent wrote:

This may not be legal in your country. You should check with the laws. The other problem is that your current may trip the off hook condition and you will not get any incoming calls.

skydiverc wrote:

If you pull over 10ma you will trip the off hook sensor at the phone company.

And according to platonas: IanP's ckt does not serve the purpose

But this circuit does not serve the purpose, it only operates when you pick-up the handset. In the on-hook position is off. And it does not convert 48V to 5V but the off-hook voltage (arround 9V-12v) to 5V.

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My circuit need continously 30mA.
I will reconsider my design and use power down modes in controller to minimizer current consumtion.