22_W_AMPLIFIER_FOR_12_V_SYSTEMS

Published:2009/7/12 23:28:00 Author:May | From:SeekIC

Power for the circuit (+12 V) is provided by a connection to the host vehicle's battery. A connection is also provided for the vehicle/s ground. Capacitors C1 and C2 provide decoupling of any sig-nal riding on the supply voltage, while capacitor C3, working in conjunction with IC1, provides ripple rejection. The incoming audio signal is coupled to IC1 by capacitors C4 and C5. Those 10-μF capacitors are used to avoid rolling off of the low audio frequencies. Resistor R1 and capacitor 06 feed the mute switch circuit (indluded in IC1), providing the delay that eliminates turn-on pop. Their R/C time constant is about 1.4 s. None of the component values external to IC1 are crucial, but major value substitutions should not be made. Pin 14 (the mute switch) of IC1 must have at least 8.5 V for the amplifier to be ON, or be held below 3.3 V to ensure that the chip stays in the mute condition. Current requirements at this pin are on the order of 40 pA in the ON condition, and 100 pA for standby. The R1/C6 combination used here (47μF and 39,000 Ω) provides enough delay to eliminate turn-on pop without having an excessive wait for normal operation. In addition to this slight delay, pin 14 gradually comes up above the 8.5-V threshold as C6 charges up, rather than coming on in-stantly, as it would if a simple switch were used. Values for C6 and RI are not crucial, but RI should be no larger than 100,000 Ω, and the R1/C6 time constant should be on the order of a second or two. Too short a time constant may not eliminate the turn-on pop; too long a time constant does not harm, except causing an irritating delay.



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