Power Supply Projects

A Collection of Innovative and Practical Design Projects

Maplin

• Publisher: Newnes
• Year: 2013
• ISBN:
  9781483293387
• Topic: Design
• Subtopic: Industrial Design

Using circuit diagrams, PCB layouts, parts lists and clear construction and installation details, this book provides everything someone with a basic knowledge of electronics needs to know in order to put that knowledge into practice.This latest collection of Maplin projects are a variety of power supply projects, the necessary components for which are readily available from the Maplin catalogue or any of their high street shops. Projects include, laboratory power supply projects for which there are a wide range of applications for the hobbyist, from servicing portable audio and video equipment to charging batteries; and miscellaneous projects such as a split charge unit for use in cars or similar vehicles when an auxiliary battery is used to power 12v accessories in a caravan or trailer. Both useful and innovative, these projects are above all practical and affordable.

1

Laboratory power

Publisher Summary

This chapter discusses power supply projects for laboratory power. Low-cost power supply is a relatively simple design that provides reliable performance and is ideal as a power supply for the home constructor. The supply makes a variety of voltage combinations available, which include variable split supply, variable single supply, a fixed 5 V, and a fixed 12 V supply. A three position, switchable current limit is also provided and the unit is capable of supplying current levels up to 1 A. Before the supply can be powered up, the transformer, PCB, and associated components must be housed in a suitable metal case. It is important that the case used has no large holes as live mains is present inside—on the primary side of the transformer—and it is important that the risk of electric shock as a result of touching any of these parts is eliminated.

Low cost power supply

A versatile power supply

Laboratory power supply

Low cost PSU

This low cost power supply is a relatively simple design that provides reliable performance and is ideal as a power supply for the home constructor. The supply makes available a variety of voltage combinations which include variable split supply, variable single supply, a fixed 5 V and a fixed 12 V supply. A three position, switchable current limit is also provided and the unit is capable of supplying current levels up to 1 A.

Circuit description

Figure 1.3 shows the circuit diagram of the power supply. The supply is based around the L200C regulator, which is capable of handling input voltages up to a maximum of 40 V and output voltages up to 30 V with programmable current limit. The circuit effectively uses two individual single power supplies i.e. a transformer with two separate secondary windings and two regulators.

Figure 1.3 Circuit diagram

A 2 A transformer is used in the design to allow plenty of headroom when the power supply is being used at a current level of 1 A. It is important that the transformer secondary voltage is not allowed to drop below the minimum input voltage for full voltage output from the regulator, as regulation would be lost.

Mains voltage is applied to transformer T1 via primary fuse FS1 and mains on/off switch S1. A mains voltage of 240 V r.m.s. on the primary of the transformer, corresponds to a secondary voltage of approximately 20 V r.m.s. The low voltage a.c. is fed to two separate bridge rectifiers (BR1 and BR2) via fuses FS1 and FS2. The output from the rectifiers is smoothed by electrolytic capacitors C1 and C2. Two completely separate unregulated d.c. supplies are produced which are then individually fed to the input of regulators IC1 and IC2. The output voltage of each regulator is determined separately by a network of resistors, switched by S3. A similar set of resistors (switched by S2) are used for current limiting purposes. S3 is also used to select single or split supply operation. Transistors TR1 and TR2 are used to drive two LEDs which indicate the status of the power supply outputs (single or split). Diodes, D1 and D2 are used to prevent voltage spikes or residual voltages from external equipment connected to the output of the supply from damaging the regulators. Fast recovery diodes are used in this application because of their fast switching characteristics. Resistors R7 and R15 ensure that the diodes are maintained in a conducting state even at very low output current levels. Capacitors C3 and C4 decouple the regulators, attenuate noise and prevent instability.

Construction

Insert and solder the components onto the PCB referring to Figure 1.2 and ...