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.
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 are made from a transparent semiconductor material which makes visible to the user the light generated when current flows through it.
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.
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.
This type of circuit is widely used as it provides reasonable regulation of the PSU and its load.
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
The regulator can be installed at fixed or variable output voltage so the circuit can be quite versatile.
The regulator IC's are not without their problems though, they can become unstable decreasing their efficiency.
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.
Also a capacitor typically 1 or 2 microfarad fitted after the regulator to remove any HF currents that may be present.
The origin of some of the text on this page is from the RSGB with additions by the web master
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