AN3539| Application Note
Maxim/Dallas > App Notes > AMPLIFIER AND COMPARATOR CIRCUITS Keywords: IBA power supply, 50watts, MAX5003, synchronous rectification, single switch forward converter
May 20, 2005
APPLICATION NOTE 3539
A 50 Watt Internal Bus Architecture (IBA) Power Supply
This article discusses a 12V/50W bus-converter that provides a well-regulated, efficient, isolated 12 volts from a 48V bus. The topology used is a single-switch forward converter with synchronous rectification. The MAX5003 is the PWM controller used in this design, which is optimized for the narrow input-voltage range of 48V, 5%.
Introduction
An Internal Bus Architecture (IBA) includes two power-conversion stages. The first stage uses a bus converter to obtain an intermediate bus voltage. The second stage uses point-of-load (POL) converters to convert the intermediate bus voltage to one or several low, well-regulated voltages to power the nearby loads. In this article we describe a 12V/50W bus converter that provides a well-regulated, isolated 12V from a 48V bus.
Power Supply Specification
q q q q q q q q
Input voltage: 48VDC, 5% regulation Output voltage: 12V at 4.2A Minimum load: zero amps Ripple: 1% peak-to-peak Isolation: 1500VAC Low cost Efficiency: > 90% Output should be short-circuit and overload protected
Power Conversion Topology
There are several power conversion topologies to choose among for this design. The chosen topology must be low cost and efficient. Due to the low cost requirement we have to choose a direct-driven, single-switch topology. The high-efficiency goal requires synchronous rectification in the secondary. The choices most suitable for this design are:
q q
Single-switch flyback with synchronous rectification on the secondary (Figure 1) Single-switch forward with primary reset winding and synchronous rectification on the secondary (Figure 2).
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