Overcurrent protective device and device for detecting overcurrent

Abstract

Free wheeling diodes are protected against an overcurrent. When counter electromotive forces E.sub.VU and E.sub.WU established in a tri-phase motor cause regenerative currents I.sub.V1 and I.sub.W1 to flow to transistors Q4 and Q6, and to a protection diode D2, it is decided that the protection diode D2 is in overcurrent state. In response to the decision, the transistors Q4 and Q6 are turned off, which allows that regenerative currents I.sub.V2 and I.sub.W2 flow in protection diodes D3 and D5 because of the counter electromotive forces E.sub.VU and E.sub.WU. The energies of the regenerative currents I.sub.V2 and I.sub.W2 are regenerated at a capacitor C. Thus, since a regenerative current which once passed by only one protection diode is divided into two current flows into two protection diodes, the overcurrent state is terminated.

Dependencies are inferred from the claim text.