This linear voltage regulator circuit provides battery voltage regulation from battery source to power micro controller system. The output can be selected by choosing the right resistor value in the feedback path. Many today’s micro controllers are featured with power down or power saving mode, and this circuit accommodates this feature by providing low power mode control on its input.
Three NiCad, NiMH, or lithium batteries can be used to produce 3V/3.3V output voltage, or one 9V battery pack for 5V output by using this linear regulator circuit. This circuit uses an ICL7611 micropower op amp and MAX872 voltage reference. This regulator can be used to replace the charge pump or a switching regulator. The dropout characteristics of this circuit depends on the characteristics of Q1. The Q1 must have a gate-threshold voltage below the lowest battery voltage when this circuit is used with low voltage like a three-cell battery.
In summary, this circuit works for input voltage range from 3V to 15V. This circuit has two mode, high power mode and low power mode that can be selected by logic at the MODE SELECT input. With Vin 6.5V, the quiescent current is 70µA when operated in high power mode and decrease to 40µA when it is used in low power mode. This circuit has maximum load power of 5mA in low power mode and 1A in high power mode.