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LM350K Fiches technique(PDF) 8 Page - STMicroelectronics |
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LM350K Fiches technique(HTML) 8 Page - STMicroelectronics |
8 / 14 page Application hints LM350 8/14 6 Application hints In operation, the LM350 develops a nominal 1.25 V reference voltage, V(REF), between the output and adjustment terminal. The reference voltage is impressed across program resistor R1 and, since the voltage is constant, a constant current I1 then flows through the output set resistor R2, giving an output voltage of: VO = V(REF) (1+ R2 / R1) + IADJ x R2. Since the 50 µA current from the adjustment terminal represents an error term, the LM350 was designed to minimize IADJ and make it very constant with line and load changes. To do this, all quiescent operating current is returned to the output establishing a minimum load current requirement. If there is insufficient load on the output, the output will rise. 6.1 External capacitors An input bypass capacitor is recommended. A 0.1 µF disc or 1 µF solid tantalum on the input is suitable input by passing for almost all applications. The device is more sensitive to the absence of input bypassing when adjustment or output capacitors are used by the above values will eliminate the possibility of problems. The adjustment terminal can be bypassed to ground on the LM350 to improve ripple rejection. This bypass capacitor prevents ripple form being amplified as the output voltage is increased. With a 10 µF bypass capacitor 75 dB ripple rejection is obtainable at any output level. Increases over 20 µF do not appreciably improve the ripple rejection at frequencies above 120 Hz. If the bypass capacitor is used, it is sometimes necessary to include protection diodes to prevent the capacitor from discharging through internal low current paths and damaging the device. In general, the best type of capacitors to use are solid tantalum. Solid tantalum capacitors have low impedance even at high frequencies. Depending upon capacitor construction, it takes about 25 µF in aluminium electrolytic to equal 1 µF solid tantalum at high frequencies. Ceramic capacitors are also good at high frequencies, but some types have a large Figure 4. Circuit |
Numéro de pièce similaire - LM350K |
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Description similaire - LM350K |
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