Transistors are used for current sources. Base drive for these transistors is derived from the main power supply VA, so that their collector current is proportional to the rail voltage. This feature holds the voltage on the cliff-amp collectors close to VA/2. The sensitivity of Iq to VA is about 3.4 mA/volt when VB is held constant; the sensitivity of Iq to VB is -15 mA/volt when VA is held constant. In a practical amplifier with a non-regulated supply, variations in power output will cause fluctuations in VA, but will not affect VB; therefore, having Iq increase slightly with power output will tend to compensate for the 3.4 mA/volt IqVa sensitivity. In the case of line voltage variations, since VA is about five times VB, the sensitivities tend to cancel, leaving a net sensitivity of about 2 mA/volt.
Description: The integrated circuit TDA1083 includes, with exception of the FM front end, a complete AM-/FM-radio-circuit with audio power amplifier. An internal Z-diode stabilizes the supply voltage at VS 13 V, which allows with the aid of a resistor and a rectifier, the circuit to be driven by a higher external supply voltage. Features: Large supply voltage range VS = 3 to 12 V High AM-Sensitivity Limiting threshold voltage Vi = 50 V Audio output power P0 = 0.7 W AFC-connection for VHF-tuner AM-FM switching without high frequency voltages Applications: AM-/FM- and audio-amplifier Circuit Diagram: Circuit diagram for One Chip AM/FM Radio with Audio Power Amplifier Datasheet for TDA1083: Download
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