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FAQ Team 13th August 2007 11:56 AM

Rectifier Types and Transformer Ratings
A rectifier converts AC current to DC. It uses one or more diodes. Diodes are like electrical one-way valves, allowing current to pass only on one half of the AC sine wave.

There are many variations of rectifiers. They are available as single diodes (which are usually used to construct a more complex rectifier) or packages of a complete rectifier usually containing 2 diodes (in the case of a valve rectifier) or 4 diodes (in the case of a solid state bridge rect).

All types have their uses and offer different properties. To use them it is useful to understand the variations in DC voltage that they can give and the requirement of AC current they need from the transformer.

Sometimes there are subtle but important differences. For instance, a full wave rectifier is often needed. A bridge will do this but only charges a following capacitor in short bursts of high current. It therefore needs a high current transformer to supply it. Compare this with a 2-diode full wave rect. This only needs an AC current supply of the same size as the DC output, but it needs a centre tap to work. The following DC smoothing components (load) also affect the performance.

These types are shown amongst others on an excellent sheet from Hammond,

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