| 摘要 |
PROBLEM TO BE SOLVED: To set a filament current limit value according to a filament condition such as the consumption of a filament. SOLUTION: In this filament current control method for controlling a filament current supplied to the filament 11 of an electron gun 10 by a filament current directive voltage, the filament current limit value is set according to a filament condition such as the consumption of the filament by limiting the upper limit of the filament current based on an execution current flowing to the filament. This filament current control device is provided with: a directive voltage generation circuit 2 for generating the filament current directive voltage by the execution current of the filament; a storage circuit 6 for storing the filament current directive voltage value; a directive upper-limit voltage output circuit 4 for outputting a directive upper-limit voltage based on the stored filament current directive voltage value; and a directive voltage clamp circuit 5 for clamping the filament current directive voltage to the directive upper-limit voltage; and limits the filament current by limiting the upper limit of the filament directive voltage to the directive upper-limit voltage. COPYRIGHT: (C)2006,JPO&NCIPI
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