Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

how to make 5volt power from phone lines

Status
Not open for further replies.

nikhilele

Advanced Member level 3
Joined
Jan 11, 2006
Messages
805
Helped
101
Reputation
202
Reaction score
76
Trophy points
1,308
Location
Bangalore India
Activity points
6,375
What is the theory and methods involved in making a 5v power supply from a phone line.
 

IanP

Advanced Member level 5
Joined
Oct 5, 2004
Messages
7,942
Helped
2,310
Reputation
4,622
Reaction score
531
Trophy points
1,393
Location
West Coast
Activity points
66,416
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:
https://pdfserv.maxim-ic.com/en/an/AN427.pdf
Instead of the MAX638 you can consider other switching voltage regulators ..

Regards,
IanP
 

sinip

Full Member level 4
Joined
Mar 22, 2006
Messages
216
Helped
13
Reputation
26
Reaction score
2
Trophy points
1,298
Location
Republika Srpska
Activity points
2,313
nikhilele said:
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

Advanced Member level 3
Joined
Jan 11, 2006
Messages
805
Helped
101
Reputation
202
Reaction score
76
Trophy points
1,308
Location
Bangalore India
Activity points
6,375
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

Full Member level 4
Joined
Aug 23, 2006
Messages
216
Helped
34
Reputation
68
Reaction score
2
Trophy points
1,298
Activity points
2,929
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

Advanced Member level 3
Joined
Jan 11, 2006
Messages
805
Helped
101
Reputation
202
Reaction score
76
Trophy points
1,308
Location
Bangalore India
Activity points
6,375
i got link from maximum

https://www.maxim-ic.com/appnotes.cfm/an_pk/1923

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

Code:
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:
Code:
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:
Code:
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
Code:
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.
.




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

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top