Electronics Principles V11

Clive W. Humphris

VOLTAGE REGULATION: Fixed Voltage Regulator.  

When exploring the Zener diode, an example of a simple power supply was used to provide voltage stabilisation independent of load current variation. This is fine when current demands are low; however, a fixed voltage regulator is a much better way.

These devices which are available in a range of both positive and negative fixed output voltages contain not only a form of Zener diode regulation, but also short circuit or over current and thermal overload protection. But more important they are much easier to use.

Firstly, determine the stabilised voltage from one of the standard packages. Provide a rectified DC supply (some degree of ripple being present is acceptable) and then connect the common point to the zero volts line.

Note. There is a requirement for some 'overhead voltage', for example 8V - 5V = 3V. In some cases this 'overhead' can be several times larger than the regulator voltage, but it may mean the need for a larger heat sinking arrangement as the voltage dropped between input and output will be dissipated as power loss across the device.

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