vaihtohäviöt

Vaihtohäviöt, also known as switching losses, are a phenomenon occurring in power electronic converters when semiconductor switching devices like transistors or diodes change their state, from on to off or vice versa. These losses are primarily due to the energy dissipated during the transition period. When a switch turns on, there is a brief moment where both voltage across the device and current through it are non-zero, leading to power dissipation. Similarly, during turn-off, the device transitions from a conducting state to a non-conducting state, and the interaction of voltage and current also results in energy loss.

The magnitude of switching losses depends on several factors. The switching speed of the device is crucial; faster switching generally leads to lower losses, but this can be limited by other device characteristics. The voltage the device must block when off and the current it conducts when on also influence the losses. Higher voltages and currents typically result in greater switching losses. The parasitic elements within the circuit, such as stray inductance and capacitance, also play a role by causing oscillations and prolonging the switching transition.

Minimizing switching losses is a key objective in power converter design. Techniques to achieve this include using devices with faster switching speeds, optimizing the layout of the converter to reduce parasitic elements, and employing soft-switching techniques. Soft-switching methods, such as zero-voltage switching (ZVS) or zero-current switching (ZCS), aim to turn the semiconductor devices on or off when either the voltage across them or the current through them is already zero, thereby significantly reducing or even eliminating switching losses. High switching losses can lead to increased heat generation, reduced converter efficiency, and a need for larger heatsinks, impacting the overall size, cost, and performance of the power electronic system.