Efficiently converting 12V AC/DC to 24V, 5V and 3.3V

摘要

This supply was designed to power a circuit with motors and solenoids that require 24V, plus digital and analog control circuitry needing 5V and 3.3V rails. It delivers all three regulated rails from a single 12V input without wasting a lot of energy or producing much heat. It is built around three integrated switchmode regulator ICs, IC1-IC3, operating as DC/DC converters. ICl operates as a boost converter while IC2 and IC3 operate in buck (step-down) mode. ICl is a high-efficiency step-up (boost) converter chip which switches at 1.2MHz. This reduces the size of the required inductor and capacitors. ICl's output voltage is adjustable up to 28V; this is set by the ratio of the resistors across the output, with the tap going to its feedback pin (pin 3).