Coordinated power sequencing to limit inrush currents and ensure optimum filtering

Abstract

A regulated power supply apparatus and method is provided. A converter circuit is configured to generate a regulated voltage signal from an unregulated voltage signal. A power sequencing circuit includes an unregulated voltage source input terminal and is configured for coupling an unregulated voltage signal to an unregulated voltage signal input terminal of the converter circuit. The power sequencing circuit includes an enable output coupled to the enable signal input terminal and includes a power limiting circuit and a trigger circuit. The power limiting circuit includes a first cascade of discrete analog components as controls for a first switching element and the trigger circuit includes a second cascade of discrete analog components as controls for a second switching element. The first cascade is configured as a charge control circuit for controlling a rate of charge of a first filter network and includes a zener diode coupled in parallel. The second cascade is configured as a detector of voltage levels and generates the enable signal. The first and second switching elements are semiconductor switches. The first filter network is coupled upstream of the converter circuit and a second filter network is coupled downstream. In an exemplary embodiment, the converter circuit is a DC to DC bus converter circuit and the regulated power supply apparatus is a fan controller circuit.