上海产77型高频大电刀脚踏开关控制的是变压器初级220V电源的通断（见图1）。使用中其固定触头松动时与开关铸铁外壳相碰，极易造成机壳带电或电源接地事故。笔者加装一废旧电动吸引器的接触器电路后，由于脚开关只与6V电源相连，从而彻底解决了这一问题（见图2）。改进时，只 Shanghai production of 77 high frequency electric knife foot switch control is the primary 220V power transformer on-off (see Figure 1). When the fixed contact is used, it collides with the cast iron shell of the switch, which can easily cause the shell to live or the power grounding. After installing a contactor circuit of a used electric vacuum device, the problem is completely solved because the foot switch is only connected to the 6V power supply (see FIG. 2). Improve only