REGULATION
Zener diode
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One of the most simple forms of regulator is the zener
diode. When a large reverse voltage is applied across a
diode the junction will break down so that current
flows. This breakdown can occur at a precise voltage,
depending on the type of material and the amount of
doping used.
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So therefore the zener diode can be used for
stabilization purposes as the reverse voltage will
remain constant even though the current may vary quite
considerably.
LIGHT EMITTING DIODES
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Light emitting diodes are made from a transparent
semiconductor material which makes visible to the user
the light generated when current flows through it.
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So the LED can be used as an indicator of current flow
or voltage present. Whilst they may need a higher
voltage than ordinary diodes to make them conduct a
series resistor is used to limit the current flow
through them to prevent destruction of the LED.
THE SERIES REGULATOR
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When a much larger current is required the zener diode
provides the base current for a power transistor
connected as a shunt or series regulator. The transistor
needs 0.6volt on its base to conduct so the collector
must be about 0.6volt above the zener voltage. In other
words choose the output voltage and make the zener diode
value about 0.6 of a volt above that.
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This type of circuit is widely used as it provides
reasonable regulation of the PSU and its load.
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Improved versions are available in integrated circuit
form, using comparator amplifiers monitoring the load
voltage and comparing it to the zener diode reference,
so driving the series transistor
INTEGRATED CIRCUIT REGULATORS
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The regulator can be installed at fixed or variable
output voltage so the circuit can be quite versatile.
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The regulator IC's are not without their problems
though, they can become unstable decreasing their
efficiency.
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Small value capacitors 0.1 0.01 microfarad type are
connected close to the regulator pins to stop HF
instability that may impair the regulator efficiency.
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Also a capacitor typically 1 or 2 microfarad fitted
after the regulator to remove any HF currents that may
be present.
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