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LM1818N 数据表(PDF) 7 Page - National Semiconductor (TI) |
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LM1818N 数据表(HTML) 7 Page - National Semiconductor (TI) |
7 / 14 page Application Hints (Continued) MONITOR AND RECORD AMPLIFIERS (Figure 6) The monitor and record amplifiers share common input and feedback connections but have separate outputs During playback the input signal is amplified and appears only at the playback monitor output Because the outputs are sepa- rate different feedback components can be used and as a result totally different responses can be set The amplifiers are stable for all closed loop gains above 3 and have an open loop gain of typically 80 dB The outputs are capable of supplying a minimum of 400 mA into a load and swing within 500 mV of either VCC or ground If more than 400 mA is needed to drive a load an external pull-up resistor on the output of these amplifiers can increase the load driving ca- pability AUTOMATIC LEVEL CONTROLALC (Figure 7) The automatic level control provides a constant output level for a wide range of record source input levels The ALC works on the varying impedance characteristic of a saturat- ed transistor The impedance of the saturated transistor forms a voltage divider with the source impedance of a se- ries resistor (R1 in Figure 9 ) The input signal is decreased as the ALC transistor is increasingly forward biased The ALC transistor will be forward biased when the preampli- fiers’s AC output (pin 14) coupled to the combination ALC- meter drive input (pin 4) reaches 40 mV peak (25 mVrms) The gain of the ALC loop is such that a preamp input signal increase of 10 dB will result ina2dB increase on the AC output of the preamplifier If greater than 25 mVrms is de- sired at the output of the preamp a series resistor can be added between the preamp output coupling capacitor and the ALC input (pin 4) The input impedance of the ALC cir- cuit is 2 kX therefore ifa2kX series resistor is added ALC action will begin at 50 mVrms The ALC memory capacitor connected to pin 6 has the addi- tional function of amplifier anti-pop control for this reason it is necessary that a capacitor be connected to pin 6 even if ALC is not used Record gain e 1 a R15 R14 Playback gain e 1 a R16 R14 TLH7894 – 8 FIGURE 6 Monitor Amplifier 7 |
类似零件编号 - LM1818N |
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类似说明 - LM1818N |
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