Share a circuit for an electric fan to stop automatically when it is electrocuted

Today I will share with you a circuit that allows an electric fan to automatically stop to prevent body touch and electric shock, and we will learn, analyze and improve together.

The above picture is a very practical circuit diagram of an electric fan to prevent body touch. In this circuit diagram, the final object of control is the electric fan's motor B1. Only when the motor stops will the fan be completely safe.

Its basic principle is this: when a person's hand touches the large metal cover P on the outside of the electric fan, the circuit responds immediately, cuts off the power supply, applies emergency braking to the motor, and finally stops the electric fan from rotating.

The basic control principle in the figure above: thyristor Q6 is used to realize control, and then the intermediate relay KA is used to control the rotation of the fan. It mainly consists of the following parts.

1. Main operating circuit: relay KA and motor B1.

2. Main control circuit: transistor Q5, thyristor Q6, relay KA, numerous resistors and large metal protective cover P of the electric fan, etc.

3. Braking circuit: capacitor C1, diode D2, and KA normally open contact.

The following is a detailed analysis of this schematic.

When we turn on the power normally, the electric fan works normally, the human body does not touch the metal cover, the transistor Q5 is in the cut-off state, the thyristor Q6 is in the off state, and the relay KA is in the released state, so its normally closed contacts are closed and the normally open contacts are disconnected, the motor M rotates normally, and the 220V AC power charges the capacitor C1 to prepare for the emergency braking of the motor B1.

When a part of the human body touches the large metal cover P of the electric fan, the first step occurs, red 1 in the figure, the induction signal on the human body is added to the base of the transistor Q5 through the resistor R8, driving the transistor Q5 to open, and then a voltage drop will be formed on the resistor R9, and the second step occurs, red 2 in the figure, the control electrode of the thyristor Q6 is triggered to turn on due to the voltage, followed by the third step, red in the figure, the relay KA is energized and the contacts of the relay will change, its normally closed contacts are disconnected, and the power supply of the motor B1 is quickly cut off. Its normally open contacts are closed, and the electricity of the capacitor C1 is added to the motor B1, so as to quickly brake the motor B1 and prevent the human body from being hurt by the fan blades.