Freewheeling diode for DC - sources

Free-wheeling diodes are used for protection against overvoltage when an inductive DC load (e.g. electric motor, relay coil, solenoid) is switched off. For this purpose, semiconductor diodes are connected in parallel to inductive DC loads so that they are stressed by the supply voltage in the reverse direction

After switching off the supply voltage, the self-induction of the coil has the effect that the current flows in the original direction. Without a freewheeling diode, this leads to a voltage peak which adds to the operating voltage and can damage or destroy the switching path. With a freewheeling diode, the voltage peak is limited to the forward voltage of the respective diode. This protects the electronic components (for example, semiconductors such as transistors), but also switching contacts very effectively from overvoltage. The current flows through the diode and the energy of the magnetic field, is largely converted into heat in the ohmic resistance of the coil and to a small part in the diode.

Typical applications are the testing of electric motors, the operation and testing of electric motors and relay coils. Specially the branches electromobility, electric motor manufacturers as well as test bench constructors appreciate this option. The free-wheeling diode (FD) option was specially developed for the DC sources of the LAB/SMP and LAB/HP series with output powers from 750 W to 1.4 MW and output voltages up to 2000 VDC.