Power Supply

Switching DC Power Supplies

Introduction

Most DC power supplies are designed to meet some or all of the following requirements:

1. Regulated output - constant output voltage Within a specified range in the input voltage and the output load current, the average output voltage changes within a specified tolerance and the output ripple voltage is below a specified value.
2. Isolation - electrical isolation between input and output The electrical isolation is referred to the DC isolation.
3. Multiple outputs - The multiple outputs can differ in voltage polarities, voltage ratings and current ratings.

Common targets for DC power supply design:

1. Small size (transformer, heatsink, filter capacitor)
2. Light weight (transformer)
3. High efficiency
4. Low construction cost

Unregulated DC power supplies: diode bridge rectifiers

Regulated DC power supplies can be divided into two types:

1. Linear power supplies - the power semiconductor devices act as adjustable series resistors (operated in active region)
2. Switching power supplies - the power semiconductor devices act as switches (either completely on or completely off)

Phase-controlled bridge rectifiers can be used as regulated DC power supplies but their output voltage response times (against input rms voltage or load change) are relatively slow.

Electrical isolation: use transformers

next Linear Power Supplies