Switch-Mode Voltage Regulator

027 SWITCH-MODE VOLTAGE REGULATOR Switch-mode power supplies offer the user the benefit of a much greater efficiency than obtainable with a traditional power supply. The switch-mode regulator presented here has an efficien- cy of around 85%. An input voltage of 12-16 V DC is converted into a direct volt- age of exactly 5 V. The use of a Type MAX638CPA enables the design and construction of the regulator to be kept fairly simple: only nine additional components are needed to complete the cir- cuit. Resistors R1 and R2 are used to indicate when the battery volt- age becomes low: as soon as the voltage on pin 3 becomes lower than 1.3 V, Dl lights. With values as shown for the potential divider, this corresponds to the supply voltage getting lower than about 6.5 V. The output of the is is shunted by a simple Lc filter formed by Ll, C3 and D2. The oscillator on board the is generates a clock frequency of around 65 kHz and drives the output transistor via two NOR gates. The built-in err...