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LM317LBZRA Folha de dados(PDF) 7 Page - ON Semiconductor |
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LM317LBZRA Folha de dados(HTML) 7 Page - ON Semiconductor |
7 / 12 page LM317L, NCV317LB http://onsemi.com 7 CL = 0.3 mF; CAdj = 10 mF Figure 16. Line Transient Response Figure 17. Load Transient Response 0.3 0.2 0.1 0 -0.1 -0.2 100 50 0 0 102030 40 t, TIME ( ms) CL = 1 mF; CAdj = 10 mF Vin = 15 V Vout = 10 V INL = 50 mA TJ = 25°C IL -0.3 CL = 1.0 mF; CAdj = 10 mF Vin 1.5 1.0 0.5 0 -0.5 -1.0 -1.5 1.0 0.5 0 010 20 30 40 t, TIME ( ms) Vout = 10 V IL = 50 mA TJ = 25°C CL = 0; Without CAdj APPLICATIONS INFORMATION Basic Circuit Operation The LM317L is a 3-terminal floating regulator. In operation, the LM317L develops and maintains a nominal 1.25 V reference (Vref) between its output and adjustment terminals. This reference voltage is converted to a programming current (IPROG) by R1 (see Figure 13), and this constant current flows through R2 to ground. The regulated output voltage is given by: Vout = Vref (1 + ) + IAdj R2 R2 R1 Since the current from the adjustment terminal (IAdj) represents an error term in the equation, the LM317L was designed to control IAdj to less than 100 mA and keep it constant. To do this, all quiescent operating current is returned to the output terminal. This imposes the requirement for a minimum load current. If the load current is less than this minimum, the output voltage will rise. Since the LM317L is a floating regulator, it is only the voltage differential across the circuit which is important to performance, and operation at high voltages with respect to ground is possible. + Vref Adjust Vin Vout LM317L R1 IPROG Vout R2 IAdj Vref = 1.25 V Typical Figure 18. Basic Circuit Configuration Load Regulation The LM317L is capable of providing extremely good load regulation, but a few precautions are needed to obtain maximum performance. For best performance, the programming resistor (R1) should be connected as close to the regulator as possible to minimize line drops which effectively appear in series with the reference, thereby degrading regulation. The ground end of R2 can be returned near the load ground to provide remote ground sensing and improve load regulation. External Capacitors A 0.1 mF disc or 1.0 mF tantalum input bypass capacitor (Cin) is recommended to reduce the sensitivity to input line impedance. The adjustment terminal may be bypassed to ground to improve ripple rejection. This capacitor (CAdj) prevents ripple from being amplified as the output voltage is increased. A 10 mF capacitor should improve ripple rejection about 15 dB at 120 Hz in a 10 V application. Although the LM317L is stable with no output capacitance, like any feedback circuit, certain values of external capacitance can cause excessive ringing. An output capacitance (CO) in the form of a 1.0 mF tantalum or 25 mF aluminum electrolytic capacitor on the output swamps this effect and insures stability. |
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