BL1240 Datasheet | SHANGHAI BELLING

.. BL1240 ELECTRONIC TWO - TONE RINGER Features Low current consumption, in order to allow the parallel operation of 4 devices. Integrated rectifier bridge with zener diodes to protect against overvoltages. Little external circuitry. Tone and switching frequencies adjustable by external ponents. Integrated voltage and current hysteresis. Description BL1240 is a monolithic integrated circuit designed to repace 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 BL1240 is higher than standard ringer. For driving a dynamic loud-speaker BL1240 can simply use a decoupling capacitor, thus eliminating the usual transformer. No current limitation is provided on the output stage of BL1240, so a minimum load DC of 50 ohm is adviced, in series with a proper capacitor. The two tone frequencies generated are switched by an internal oscillator in a fast sequence and made audible across an output amplifier in the loud-speaker, 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 variatins of the ringing signal cannot affect correct operation of the device. http://.belling..cn -1- 8/14/2006 Wrote by 2006 Total 5 Pages Pin connection 1 2 3 4 Pin 1 2 3 4 5 6 7 8 Symble LINE GND Csw RA OUT NC Cr LINE Function Description Telephone line Ground Sweep rate control capacitor Output frequency control resistor Output frequency frequency Not connected Rectifier capacitor Telephone line http://.belling..cn -2- 8/14/2006 Wrote by 2006 Total 5 Pages BLOCK DIAGRAM TELEPHONE LINE 8 IN RECTIFIER CAPACITOR 7 N.C. 6 THRESHOLD CIRCUIT WITH HYSTERESIS BUZZER 5 + RECTIFIER BRIDGE OUTPUT STAGE SWITCHING FREQUENCY...