60_W_SWITCHING_AMPLIFIER

Published:2009/7/12 23:32:00 Author:May | From:SeekIC

The schematic for the switching amplifier is shown. A separate 51-Vdc source is required to power the amplifier circuit. The 51-Vdc source is fed to a pair of zener diodes, D5 and D6, and is fi1tered by capacitors C11 and C12 to provide a 12-Vdc source for part of the circuit. Also, part of the 51-Vdc source bypasses the zeners to power the sections of the circuit that require a high voltage. The right and left signals are input to the amplifier through jacks J1 and J2, respectively. Two sections of a TL074 op amp, IC1-c and IC1-d, generate a 4-V p-p, 50-kHz triangular reference waveform. The generated waveform is then fed to potentiometer R19. That enables the amplifier to use input signals with amplitudes ranging from 1 V p-p to 4 V p-p. The other two op-amp sections, IC1-a and IC1-b, function as comparators to produce the pulse -width-modulating output for the left and right channels of the amplifier. In the right channel of the amplifier, the output of the voltage comparator is coupled to the bipolar translating circuit through a current-limiting resistor, R5. The translating circuit has a positive and a negative leg; Q1, D1, and R7 make up the positive leg, and Q3, D3, and R11 make up the negative leg. Both legs are tied to ground through the emitters of Q1 and Q3, providing a reference point for the translator. The translator arrangement results in 17 V being present across Q1, Q3, and zener diodes D1 and D3. Sufficient current is then present to overcome the power MOSFET gate capacitance; that rapidly switches on and off the power MOSFET complementary push-pull output stage, composed of Q5 and Q7. Resistor R3 keeps the output swing centered at the midpoint of the supply voltage. Without R3, the square-wave output drifts down toward the negative rail. The RC network, composed of R9 and C5, which connects to both N- and P-channel gates, minimizes switching noise and sharpens the square-wave output. Note that both channels contain power-supply elements to split the incoming single-polarity voltage in half. Capacitors C3, C4, C7, and C8 make up a series-parallel circuit that converts the 51-Vdc supply to 25.5 Vdc. The output can feed full-range 60-W rms speakers, which demodulate the signal and produce an amplified audio output. (At peak output power, the current draw for an 8- Ω dynamic load is approximately 1.2 A at 51 Vdc.)



Reprinted Url Of This Article:
http://www.seekic.com/circuit_diagram/Amplifier_Circuit/60_W_SWITCHING_AMPLIFIER.html

Print this Page | Comments | Reading(3)