Overview
The LS1240A, produced by STMicroelectronics, is a monolithic integrated circuit designed to replace the mechanical bell in telephone sets. It is part of the electronic two-tone ringer family and is intended for use with electro-acoustical converters. This IC can drive either a piezoceramic converter (buzzer) or a dynamic loudspeaker directly, eliminating the need for a transformer when using a loudspeaker.
The LS1240A is characterized by its low current consumption, allowing for the parallel operation of up to four devices. It features an integrated rectifier bridge with zener diodes for overvoltage protection and requires minimal external circuitry. The tone and switching frequencies can be adjusted using external components, and the circuit includes integrated voltage and current hysteresis.
Key Specifications
| Parameter | Symbol | Value | Unit |
|---|---|---|---|
| Calling Voltage (f = 50 Hz) Continuous | VAB | 120 | Vrms |
| Calling Voltage (f = 50 Hz) 5s ON/10s OFF | VAB | 200 | Vrms |
| DC Supply Current | IDC | 30 | mA |
| Top Operating Temperature | Topr | -40 to +70 | °C |
| Storage and Junction Temperature | Tstg | -65 to +150 | °C |
| Thermal Resistance Junction-ambient | Rthj-amb | 100 | °C/W |
| Supply Voltage | Vs | 26 | V |
| Current Consumption Without Load | IB | 1.5 - 1.8 | mA |
| Activation Voltage | Von | 12.2 - 13.2 | V |
| Sustaining Voltage | VOFF | 8 - 9 | V |
| Differential Resistance in OFF Condition | RD | 6.4 kΩ | kΩ |
| Output Voltage Swing | VOUT | Vs - 5 V | V |
| Short Circuit Current | IOUT | 70 mA | mA |
| Output Frequencies | fOUT1, fOUT2 | 1.74 - 2.14 kHz, 1.22 - 1.6 kHz | kHz |
| Sweep Frequency | fSWEEP | 5.25 - 9.75 Hz | Hz |
Key Features
- Low current consumption, allowing for the parallel operation of up to four devices.
- Integrated rectifier bridge with zener diodes to protect against overvoltages.
- Minimal external circuitry required.
- Tone and switching frequencies adjustable by external components.
- Integrated voltage and current hysteresis.
- Can drive directly a piezoceramic converter (buzzer) or a dynamic loudspeaker without a transformer.
Applications
The LS1240A is primarily used in telephone sets to replace mechanical bells. It is suitable for any application requiring a two-tone ringer with low current consumption and adjustable tone frequencies. This includes:
- Telephone systems
- Alarm systems
- Audio signaling devices
- Electro-acoustical converters
Q & A
- What is the primary function of the LS1240A IC?
The LS1240A is designed to replace the mechanical bell in telephone sets, acting as an electronic two-tone ringer.
- What types of devices can the LS1240A drive?
The LS1240A can drive directly a piezoceramic converter (buzzer) or a dynamic loudspeaker.
- What is the maximum calling voltage the LS1240A can handle?
The maximum calling voltage is 120 Vrms continuously and 200 Vrms for 5s ON/10s OFF.
- What is the typical current consumption of the LS1240A?
The typical current consumption without load is 1.5 to 1.8 mA.
- How can the tone and switching frequencies be adjusted?
The tone and switching frequencies can be adjusted using external components such as resistors and capacitors.
- What is the purpose of the integrated rectifier bridge with zener diodes?
The integrated rectifier bridge with zener diodes is used to protect against overvoltages.
- What is the recommended minimum load for the output stage?
A minimum load DC of 50 Ω is advised, in series with a proper capacitor.
- What are the typical output frequencies of the LS1240A?
The typical output frequencies are 1.74 - 2.14 kHz and 1.22 - 1.6 kHz for fOUT1 and fOUT2, respectively.
- Is the LS1240A still in production?
No, the LS1240A is no longer manufactured and is considered an obsolete product.
- What are the operating temperature ranges for the LS1240A?
The operating temperature range is -40 to +70 °C, and the storage temperature range is -65 to +150 °C.
