| 摘要 |
PURPOSE:To automatically correct an applied voltage using a simple power supply by connecting a voltage control transistor circuit to one end or both ends of resistance voltage divider that is connected to an accelerating power supply and fine-adjusting the voltage for an electrostatic lens. CONSTITUTION:In a high voltage power supply for an electrostatic lens, the output Va of an arithmetic amplifier U1 is given by the following formula, Va=(R5/R3)ES. Supposing that the variable range of reference voltage ES is 0--10V and the gain (R5/R3) is 100, Va varies continuously within the range of 0-1,000V and the voltage between the collector and emitter of a transistor Q1. As the potential Va at a point (A) varies continuously, the potential at each of the tap points of a resistance voltage divider R2 also varies continuously. As a result, the voltage that is taken out from these tap points and is applied to an electrostatic lens 6 also varies continuously and the fine adjustment of a focal point is made possible. That is, even when a sample 8 is tilted, voltage can be applied to the electrostatic lens depending upon the slant by applying a control signal to the negative input point P of the arithmetic amplifier U1 through a resistor. |
