The above picture is a structural diagram of a typical Double pole micro switch（SPDT）. We can understand the basic working principle of the micro switch through this structural diagram.
When an external mechanical force acts on the button of the micro switch, the force is transmitted to the Snap-acting blade of the micro switch through the button. As the force gradually increases, the return spring plate and stores potential energy during the deformation process, while the moving spring moves to a critical point. Once this critical point is exceeded, the moving spring will produce an instantaneous action, causing the mobile contact at the end of the spring to contact or separate from the fixed contact, achieving the function of circuit switching.
After the release of the external mechanical force, the deformed return spring plate releases the potential energy stored during the bending deformation and converts it into mechanical kinetic energy output, resetting the connected Snap-acting blade to its initial state, and the mobile contact at the end of the spring once again contacts or separates from the fixed contact.
The following figure is a schematic diagram of the working principle of a typical double-throw micro switch. In the initial state, the Common terminal C (1) is connected to the NC terminal (2) through the mobile contact, and the NO terminal (3) circuit is cut off. When the button of the micro switch is pressed, the mobile contact separates from the NC terminal (2) and then contacts and connects with the NO terminal (3), at which point the NC terminal (2) circuit is cut off and the NO terminal (3) circuit is connected.
Generally speaking, the Snap-acting blade of the micro switch’s moving spring is independent of the external force and the speed of the transmission element, so the micro switch has the characteristics of high sensitivity, small contact point spacing, short travel distance, low pressing force, and fast on-off switching. Therefore, it is widely used in household appliances, toys, office equipment, machinery, automobiles and other fields.
