Lepojännite

Lepojännite, or no-load voltage, is the voltage present at the output of an electrical source when the circuit is open and no current flows. It is also described as the open-circuit voltage. The concept is used across transformers, generators, power supplies and solar cells to characterize the unloaded performance of a source.

In transformers and electric machines, lepojännite refers to the secondary (or generated) voltage when the output is not connected to a load. In an ideal transformer, the no-load voltage equals the rated secondary voltage, while the primary current is limited to magnetizing current. In practice, winding resistance, core losses and regulation cause deviations from the nominal value. The no-load voltage is a key part of defining voltage regulation, which describes how much the output changes from no-load to full-load conditions.

In power supplies and regulators, lepojännite indicates the voltage the output tends to reach when the load is minimal or absent. Under load, the output voltage typically changes due to source impedance and regulation characteristics. Designers specify both the no-load and full-load voltages to characterize performance and to ensure stable operation within tolerance.

Measurement and considerations: lepojännite is measured with a high-impedance voltmeter to avoid loading the source. Temperature, aging, and circuit configuration can shift the value, and safety precautions are essential when testing energized equipment.

Related concepts include open-circuit voltage, voltage regulation, and, in photovoltaics, the open-circuit voltage (Voc) versus short-circuit current (Isc) and maximum power point.