Transformer regulation is a measure of the
voltage rise on the secondary due to off-load or
light-load conditions with the primary input voltage
remaining constant. This measure is expressed as a
percentage of the secondary voltage; for example, a
transformer with 10% regulation and rated at 12v at full
load will have an off-load voltage of
13.2v.
Regulation is calculated as:
Due to the design
characteristics of transformers, regulation varies
inversely with power rating (VA) and is approximately
linear for any given loading on the secondary. In the
above example, if the load was 50% of full load, the
voltage would be 5% higher, or 12.6v. This regulation
figure must be borne in mind when designing rectifier
power supplies, etc. as it will affect the voltage
rating of reservoir capacitors, voltage regulators,
etc.
Custom transformers can be designed with
very low regulation figures but only at the expense of
size and weight, as larger cores and wire gauges must be
used. Following are some typical regulation figures for
standard transformer VA ratings.
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