Question

Explain how dropout voltage is important when considering different power sources (battery, AC power, etc.)

Answer 1

The dropout voltage is the difference between the output voltage and the input voltage at which the circuit quits regulation with further reductions in input voltage. It is usually considered to be reached when the output voltage has dropped to 100 mV below the nominal value.

The dropout voltage is also defined as the minimum voltage drop required across thee Regulator to maintain output voltage regulation.

The Dropout Voltage of a regulator is the amount of voltage that a regulator needs to be fed above its rated output voltage to maintain the output voltage.

a voltage regulator is a device which accepts an input voltage which it regulates down to the output voltage which it is rated for. In order for a voltage regulator to output its rated voltage, it must be fed a voltage that is higher than its rated voltage. The amount of voltage higher that the input voltage must be than the output voltage is the dropout voltage of the regulator.

For example, a LM7805 voltage regulator is a regulator that outputs 5 volts. However, in order to give out 5 volts, it needs to be fed a higher voltage as its input. The LM7805 needs at least 2 volts higher than the 5 volts to do provide the 5 volts. Therefore, it needs 7 volts as its input. Thus, its dropout voltage is 2 volts, since 5 volts + 2 volts= 7 volts.