Electronic Laboratory?

Question

I have been given the following:

You are to construct and test a variable voltage power supply based on an LM317L three terminal adjustable output voltage regulator. The voltage should be adjustable from 1.2 to 12 volts, using potentiometer built into the breadboard. The test load will be a 12 volt 960 mW lamp.

You will be expected to:
Verify that the transformer supplied for this assignment can supply 15 volts at 6VA by testing it in an appropriate manner (loading).
Construct a bridge rectifier, understand smoothing, and be able to specify the maximum voltage that the smoothing capacitor will have to withstand.

I know it's quite complicated but ... anyway, if anyone knows anything about it or any website which is related to this experiment, please don't hesitate to answer.

Answer 1

This is not complicated at all.

LM317 is an IC device with only 3 terminals. Here's an URL to the diagram:

http://www.national.com/pf/LM/LM317.html

You willneed a transformer, full bridge rectification circuit, and filters. You need to spec the transformer so that the output of the rectifier/filter is at 15V DC at full load. Notice that under no load, the ouput will be at sqrt(2) * (ac voltage). Under full load, it should drop to the RMS value of the outout. (basically means to use the 15V transformer)

The filter capacitor must be large enough so that ripple will be at minimum at the full load. 4700microF or larger should be sufficient.

Remember to heat-sink the 317, as it will get quite warm at full load.

Answer 2

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