| 摘要 |
PURPOSE:To prevent an abnormal voltage from being developed at the movable terminal of a variable resistance by adding a semiconductor switch to a mechanical switch. CONSTITUTION:A diode 11 as a semiconductor switch is connected between a terminal 10a of the mechanical changeover switch 10 and a resistance 7 and a transistor (TR)12 is connected between a resistance 8 and the ground. The base of this TR12 and the terminal 10a are connected together through a resistance 13. When the movable terminal 14 of the switch 10 is between terminals 10c and 10a, the voltage at the movable terminal of the variable resistance 1 is determined by the resistances 1, 3, and 4. Then when the movable terminal is connected between movable terminals 10a and 10b of the switch 10, the diode 11 and TR12 is conducted at the same time to connect the resistance 7 to the resistance and the resistance 8 to the resistance 4 in parallel respectively. |
