Electric feeding circuit for load with floating earth - uses reference potential to avoid potential drift at load terminals with control resistance

摘要

The electric feeding circuit for a load (1) with floating earth from a dc source (2) comprises a protection system (5) against variations of potential at the load terminals (18, 19) by connection to an intermediary reference potential. The control resistance (10) is connected via two diodes (11, 12) through a resistance (13) to the reference potential (earth) and is also connected via two diodes (14, 15) each in series with a large resistance (16, 17) to the load terminals. The control resistance (10) creates a voltage drop which triggers the protection system when the potential at one of the two load terminals tends to drift and overshoot the reference value. The protection system consists of a differential amplifier (6), a comparator (7), a rectifier (8), and a control circuit (9) which acts on the source voltage. A threshold voltage, U, is applied to the comparator which then determines the operating threshold of the control circuit.