Power amplifier LM3886, LM3886 power amplifier
Keyword: HI-FI, LM3886, amplifier, power amplifier
Description: The maximum feature of this self-protection IC is functional, no external various protection circuits, it contains NS company developed SPIKE (itself instantaneous temperature) protection circuit safe operating area of the output stage transistor (SOA) dynamically detection and protection, in order to fully achieve overvoltage, undervoltage, overload, short circuit output (including short-circuited to ground short circuit to the power supply), and transient thermal runaway temperature shock protection function
LM3886 is monaural, the power, high-performance audio power amplifier IC, National Semiconductor (NS)'s "Prelude" (Overture) having one of series of audio amplifier IC representative. It uses 11-pin TO-220 package and has input mute functions, suitable for small active speakers, surround acoustic amplifiers, and high fidel stereo televisions.
LM3886 main performance profile
1, a continuous average output power: 60W / 4Ω (Vcc = ± 28V) 30W / 8Ω (Vcc = ± 28V) 50W / 8Ω (Vcc = ± 35V) 2, the instantaneous maximum output power: 150W3, distortion: (THD + Noise) 0.03% (20Hz ~ 20kHz) 4, noise level: 2.0μV5, signal to noise ratio:> 92dB6, intermodulation distortion :( by SMPTE standard) 0.004%
The maximum feature of this self-protection IC is functional, no external various protection circuits, it contains NS company developed SPIKE (itself instantaneous temperature) protection circuit safe operating area of the output stage transistor (SOA) dynamic detection and protection The protection function such as overpressure, undervoltage, overload, output short circuit (including short-circuiting and short-circuiting), thermal out-of-control and instantaneous temperature shock. Figure 1 is an equivalent circuit of an internal 3886.
Circuit works Brief
Be
R2 provides to the noninverting input of LM3886 bias; C2 in parallel with two input terminals is used to reduce the high frequency gain of the amplifier, so the output tube oscillate while suppressing electromagnetic interference noise input; R5, R4, C4 composition feedback loop, low-frequency and high frequency response corner frequency fH amplifier depends R3, C3; R4, C4, R5 and R3 determines the gain and high frequency low-pass corner frequencies fL (fH, fL formula slightly).
C4 is a compensation element which with R4, R5 together act to reduce the high frequency gain.
R8, R9, C5 and switches (shown in broken line in FIG.) Consisting of the mute control circuit: When the switch is turned off, stopping the output of the LM3886, i.e. mute function; released when the mute switch is turned on, R8 the output current is limited to a pin ⑧ 0.5 mA (the 8 foot current of LM3886 is ≥ 0.5mA). C5 is martial inspiration, offering a large time constant.
Effect R6, C6 to prevent generation of high frequency oscillation amplifier.
L1, R7 effect: If the load is accompanied (such as the speaker cable), the amplifier is overloaded at high frequencies, and the square wave response is turned to avoid this, and the parallel circuit consisting of LR in the output end. at this time showed a larger inductance L, 10 [Omega] resistor and the capacitive load of the amplifier to isolate and reduce the Q value of L and the capacitive load circuit configuration; at low frequencies is 10 [Omega] resistor is short-circuited by L, a small inductance amplifier L-driving the load directly.
A few remarks made in matters
150W Hi-Fi amplifier circuit described herein, see FIG. 2 FIG. Since the series of pins of the IC compatible with each other, as shown in FIG. 3 so that the printed circuit board can be installed LM3876 (50W), can also be used to install LM3886 (150W), for this purpose, the circuit IC1 ⑤ feet contact plate to the power supply, to suit the LM3886, LM3876 and during installation, since the NC terminal ⑤ feet (no internal connection), it is still suitable.
For optimum performance, a C7 ~ C10 with a power supply decoupling circuit board and all the ground is a ground point; IC1 mounted in the side of the circuit board, so as to secure it to the radiator, radiator The thermal resistance is less than 1.5kΩ / W.
Available air core inductors L1 enameled wire wound on 10mm 1mm tire tool 13 were derived from ring; L1 mounted inside a resistor R7, and their ends soldered to the circuit board parallel.
MUTE termination on this circuit a switch, when the switch is turned off, i.e., in a mute state of ICl; muted if required, should be on the short-circuiting wire section MUTE end welding. R6 ~ C6 improved stability for high-frequency amplifier is usually omitted, but should add.
The LM3886 (or LM3876) optimum load is 8 ohms, if for 4Ω load, when the power supply voltage drops to about 27V, the internal protection circuit IC1 SPIKE function, the output power is reduced to about 10W. Therefore, the impedance of the speaker is best not less than 8Ω.
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