| 摘要 |
An embodiment of the present invention provides an excitation arrangement suitable for use in producing a pulse-shaped field of substantially constant intensity. To start-up the current at the beginning of a pulse, a coil (1) is fed with a high voltage (line 3) via an ignitable and blockable power semiconductor (7). For the duration of the pulse, switch-over is then effected to the supply of a lower voltage (line 4) by means of a power transistor (31) controllable to a constant current. Free-running diodes are used to decay the current. One coil end (2) is preferably connected via an FET (7) which is controllable to a constant voltage, to the high voltage; via an FET (30), which is likewise controllable to a constant voltage, to the lower-voltage (4); and via a controllable FET (52) to a reference line (6). Corresponding FET's (50, 51, 31) are provided at the other coil end (5). The controllable FET's (51, 52) require no potential-isolated control, and moreover, the power-FET's do not require their own additional free-running diodes (mentioned above) due to their inherent diode characteristic for currents flowing in the blocking direction.
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