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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: power from phone line
Summary: Telephone ringing voltage...
Keywords: phone, power, remote
Message-ID: <3544@kitty.UUCP>
Date: 8 Dec 89 04:41:09 GMT
References: <14230@jumbo.dec.com> <3542@kitty.UUCP> <6300@lindy.Stanford.EDU> <5651@internal.Apple.COM>
Organization: Recognition Research Corp., Clarence, NY
Lines: 22

In article <5651@internal.Apple.COM>, ems@Apple.COM (Mike Smith) writes:
> Vague memory from too many decades ago... I think the ring signal is 
> pulsed DC at about 50 V and the current is 'all the inductor can carry'...

	Ringing voltage is typically 20 Hz AC @ 105 volt RMS upon which is
superimposed -50 volts DC (with respect to ground).  The DC component is
present to facilitate operation og a "ring-trip" relay or solid-state
circuit.

	The telephone ringing supply is traditionally current limited to
about 100 mA by a resistance lamp (i.e., ballast lamp).  Resistance lamps
are still used in much ESS apparatus due to their inherent simplicity and
reliability.  Newer ESS apparatus uses solid-state circuits for ringing
supply current limiting.

	Ringing voltage is not applied to a telephone line through an
inductor, so there is no current limiting by that means.

<> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp.
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