Exact match. Not showing close matches.
'[EE]: Powering a PIC from the Phone Line'
Sometimes you need to power a microcontroller from the phone line for
example in a Caller ID unit or a line powered modem.
This is fine when the phone is offhook and you have several milliamps to
enjoy. However, when you are on-hook and you can only draw a maximum of
50uA from the 50V phone line (2.5mW), you need to use some smart-thinking
to keep your microcontroller alive.
If you are running a RTC from a 32kHz crystal, such as is possible on any
of the small PICs (but more conveniently the F628 and F877 which have a
second oscillator) you can get by on about 15 or 20uA. This is easily done
using a 1megohm dropper resistor from the front end bridge rectifier to
provide a leakage supply which charges a capacitor. This is how most modern
phones are powered.
If you need more power then a simple buck converter can be made from a 4060
CMOS counter, an couple of high Vce transistors and a dozen or so passive
components. The whole lot will fit onto 3 square inches of pcb space -
using conventional components and a DIL 4060.
I have one running on a bit of stripboard and it produces 300uA at 5V
making it about 60% efficient overall. Total cost - about $3.
Access to the schematics is via the Rat_Ring group site, and you can
subscribe to that from here:
Rat_Ring is a discussion forum for those interested in telephony and telecom
applications of PICS
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads
More... (looser matching)
- Last day of these posts
- In 2001
, 2002 only
- New search...