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EL-06 August 9, 1995

[Filename: DC_PWR.DOC]

DC Power Supply Design and Printed Circuit Board Layout

Contributor: Rob Jarman

Affiliation Address: Electrical Engineering

University of Technology, SydneyPO Box 123

Broadway NSW 2007

Australia

Telephone: +61 2 330 2368

Facsimile: +61 2 330 2435

Email: [email protected]

Type: Design Problem

Student time: 5 to 7 weeks

Location: Take home

Summary

This is intended to be distributed to junior electrical engineering students in the early

weeks of semester as a design problem. Students work individually from a given scenario

to complete the electrical analysis and printed circuit board layout for a simple DC power

supply.

Material required to be covered includes transformers, diode rectification, capacitive

filtering and voltage regulation. As the material is completed, students have an immediate

application to test their analytical skills in selecting components to meet the specification.The Printed Circuit Board (PCB) design has some constraints including physical

dimensions, mounting holes and single sided design. Students need to research vendor

catalogues to determine the component package outlines and pin spacing. Alternatively,

these could be supplied as an additional handout to students. Component overlays can be

obtained from PCB CAD packages. The PCB design is usually completed by hand on an

overhead projector transparency film using permanent markers.

An extension exercise is included, students are to develop an over-voltage protection

circuit to be connected to the output of the DC supply.

ABET Descriptors

Engr. Sci Content: Electrical, circuits, electronics

Type: System, component

Elements: Establish requirements, analysis, synthesis

Features: Design methodology, detailed system descriptions

Constraints: Safety, reliability

Effort: Individual

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Students shall work independently on the project.

A 110VAC 60Hz renewable energy power generator system requires a DC power supply

module. The module is to provide a variable DC voltage signal proportional to the AC

voltage generated as well as supplying a fixed 5VDC to supply the electronic system

controller.

The variable DC signal is used by the electronic system controller as a feedback system to

monitor the voltage being generated. As the voltage generated increases or decreases, the

DC voltage increases or decreases. The specification for this module is 1VDC per 12VAC

and the maximum current drawn by the feedback circuit is 10mA.

The electronic system controller uses TTL and CMOS Integrated Circuits which require a

regulated 5VDC 2% supply, maximum current load is 500mA.

A dual secondary transformer is already available and assumed to be suitable. Its

specifications are :

input voltage 110V AC

output voltage 15V 0V 15V 0V

VA rating 40VA

Select a suitable circuit topology and specify component ratings.

Design a printed circuit board layout for the module using component dimensions and pin

spacing obtained in local vendor catalogues. The design constraints are that the PCB be as

small as possible, interconnecting terminals must be provided, it must have some means by

which it is mounted in a control panel, it must be single sided (copper on one side only)

and all components for the circuit (excluding the transformer) should be mounted on the

PCB.

Optional extension exercise

Design a circuit and specify the components necessary to ensure that the voltage sensitive

TTL components in the electronic system controller are protected against voltages greater

than 5.5VDC.

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Project deliverables

A report is required detailing the analysis and selection of components for your design.

The PCB layout should include a component overlay under the transparancy for

assessment purposes.

Evaluation Criteria

Detailed report (Word Processor)

Drawings (CAD or suitable quality hand)

PCB layout: dimensions, layout of components, interconnection, thermal, trackand pad size, circuit protection, mounting arrangement

Circuit operation: will it work, size and ratings of components, analysis, limits of

operation, prediction of waveforms around the circuit

Optional exercise: analysis, ratings of components, limits of operation

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Engineering Notes:

To begin with, students typically have a hard time understanding all of the requirements of

this design problem. As each week passes, more material is covered and students see animmediate application for the knowledge they are learning.

A block diagram is useful to help students understand how and where in the system the

DC power supply module fits in.

The renewable energy source could typically be hydro or wind, the generator could be a

self exciting type.

Typically considered in the assessment of the circuit design include calculation and

justification for the transformer primary winding fuse protection, transformer output

winding connection, rectifier diode selection, filter capacitor selection, regulator selection,

decoupling and transient capacitors, regulator protection diodes, thermal analysis of

regulator power dissipation.

Typically considered in the assessment of the printed circuit board design includes:

interface/interconnection methods, component selection, component layout, thermal

layout, solder pad size, track width, PCB dimensions, PCB mounting technique, minimize

area of PCB, consideration of assembly, repairable design.

Renewable

Energy

Source

240V 50Hz

Generator Consumer

1VDC per

12VAC

5VDC fixed

voltage

regulator

Electronic

system

controller

DCpower

supply

module

Transformer

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The optional extension exercise is included for students who might need an extra

challenge. Discrete designs using zeners and SCRs are typical, also available is a range ofASICs.

Intended learning outcomes for students from this project include:

Development of the circuit and component selection in electrical engineering

science.

Development of skills in determining the specifications of a project.

Application of analysis skills to a problem in a physical context.

Development of synthesis skills in determining a solution to the problem.

Exposure to best practice PCB layout and assembly techniques for safety and

reliability.

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