With National Semiconductor's new LM4651 and LM4652 design of 125 W D category for ultra low-power amplifier circuit as shown below. The amplifier in the total harmonic distortion THD = 1% of the output power of 125 W, load impedance RL = 4 Ω, the input signal Vin (rms) for the most high-3 V, the input signal bandwidth of 10 ~ 150 Hz, ambient temperature of 50 ℃, Power supply voltage to ± 20V.
In a 28 pin DIP package is the LM4651 PWM control / driver IC, built-in oscillator, PWM comparison, the error amplifier, the feedback amplifier, power-shift and high-end drives, low-end drive and under-voltage, overheating, short circuit and over - Modulation protection circuit. LM4652 is a 15 foot (including 6,8,9, (11), (12) feet is not connected) TO-220 package of half-bridge power MOSFET IC, 4 MOSFET the breakdown voltage V (BR) DSS = 50V , The drain current ID = 10A, open-resistance RDS (ON) = 200m Ω (typical), open voltage VGS (th) = 0.85V (typical).
LM4651 in the oscillator frequency fosc = 1 × 109 / (4000 + Rosc), which Rosc = R6 = 3.9k Ω, therefore fosc = 125kHz. Enter audio signal C1, R1 and 10 feet into the gain of 7 5 V / V (that is, 17 5 dB) of the error amplifier. IC27 legs and feet (15) the half-bridge switching output by RC filter after feedback to the IC1 (14) feet, 19) (feet by internal feedback measuring 9 feet from the amplifier output after 10 feet, providing for the error amplifier A single-ended feedback signal. Audio input signal and the triangular wave oscillator to compare, in comparison with PWM output produce a factor of the air and the incoming audio signal level is directly proportional to the square wave pulse, to drive IC2 in the power MOSFET. IC27 legs and feet (15) the switch output, the L1, C16 and L2, C17 low pass filter, and promote speakers work.
IC1 (18) feet of the resistance R4 for short-circuit current limit. When R4 = 100k Ω, short-circuit current level of not less than 10 A; (17) feet of the resistance R5 set for the dead time; (24) feet of the capacitor C9 set for launch delay time (one second) , (13) feet (STOBY) at the logic "1" or 5 V, the standby function to stop PWM, the shutdown of the LM4652 power switch, only a very low current consumption. IC2 as long as the junction temperature reached 150 ℃, its 4 feet of output feedback to the IC1 (12) feet, can perform functions of the closure.
Following is the circuit :
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