August 2006

Rev 2

1/9

9

LS1240

Electronic two-tone ringer

Features

parallel operation of 4 devices

protect against over voltages little external

circuitry

external components

Description

LS1240 is a monolithic integrated circuit designed

to replace the mechanical bell in telephone sets in

connection with an electro-acoustical converter. It

can drive directly a piezoceramic converter

(buzzer) or a dynamic loudspeaker.

The output current capability of LS1240 is higher

than the one of a standard ringer. To drive a

dynamic loudspeaker LS1240 can simply use a

decoupling capacitor, thus eliminating the usual

transformer.

No current limitation is provided on the output

stage of LS1240, so a minimum load DC of 50

Ω

is advised, in series with a proper capacitor.

The two tone frequencies generated are switched

by an internal oscillator in a fast sequence and

are made audible across an output amplifier in the

loudspeaker. Both tone frequencies and the

switching frequency can be externally adjusted.

The supply voltage is obtained from the AC ring

signal and the circuit is designed so that noise on

the line or variations of the ringing signal cannot

affect correct operation of the device.

Pin connection (top view)

Minidip

SO8

www.st.com

Obsolete

Product(s)

- Obsolete

Product(s)

Obsolete

Product(s)

- Obsolete

Product(s)