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.
General description: The TDA8946J is a dual-channel audio power amplifier with an output power of 2 × 15 W at an 8 Ω load and a 18 V supply. The circuit contains two Bridge Tied Load (BTL) amplifiers with an all-NPN output stage and standby/mute logic. The TDA8946J comes in a 17-pin DIL-bent-SIL (DBS) power package. The TDA8946J is printed-circuit board (PCB) compatible with all other types in the TDA894x family. One PCB footprint accommodates both the mono and the stereo products. Features: Few external components Fixed gain Standby and mute mode No on/off switching plops Low standby current High supply voltage ripple rejection Outputs short-circuit protected to ground, supply and across the load Thermally protected Printed-circuit board compatible Circuit Diagram: Circuit Diagram for 2 x 15 W stereo Bridge Tied Load (BTL) audio amplifier PCB layout: PCB layout TDA8946 Datasheet for TDA8946J: Download
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