Conversion of electrical energy to mechanical energy - How to drive the solenoid valve in the circuit

Solenoid valves are one of the most common actuators in many automated process systems. There are many different types of solenoid valves, such as those used for water supply switches or gas pipes, and some solenoid valve pistons are used for simple linear piston movement. One of the most common applications we see is the doorbell. The doorbell has a piston-type solenoid valve coil that moves a small rod inside it when it is energized by an AC power source. The rod hits the metal plates at both ends of the solenoid valve to produce the "ding dong" sound.

Although there are many different mechanisms for solenoid valves, the basic principle remains the same. It consists of a coil of wire wrapped around a metal (conductive) material. When the coil is energized, the conductive material undergoes some kind of mechanical movement, and when it is de-energized, a spring or other mechanism reverses the movement. Because solenoid valves contain coils, they consume a lot of current, so they must be operated through some kind of drive circuit. Here we will describe how to build a drive circuit for a solenoid valve.

Required components

Solenoid valve
12V power adapter
7805 regulator
IRF540N mos
IN4007 diode
0.1uF capacitor
1kΩ and 10kΩ resistor

Working principle of solenoid valve

A solenoid valve is a device that converts electrical energy into mechanical energy. It consists of a coil wrapped around a conductive material, which makes it an electromagnet. The advantage of an electromagnet over a natural magnet is that it can control its activation by energizing the coil as needed. According to Faraday's law, a magnetic field surrounds the conductor through which current flows, and the magnetic field between the coils can be large enough to magnetize the material and produce mechanical movement.

In this process, the coil will absorb a lot of current and cause hysteresis, so it is not feasible to drive the solenoid valve directly through the logic circuit. Here we use a 12V solenoid valve that is commonly used to control the flow of liquids. After charging, the solenoid valve will absorb 700mA of continuous current and the peak value is close to 1.2A. So we must take these values ​​into account when designing the circuit.

Circuit diagram

As you can see, the drive circuit is not complicated. We can complete the above connections with a simple breadboard. The solenoid valve can be opened by passing 12V voltage through both ends and closed after removing the power supply. In order to control this switching process, we need to design a switching circuit, so the MOS tube is also an important part of the circuit. The following are the parameters that need to be paid attention to when selecting the MOS tube.

Turn-on voltage Vgs(th): This is the turn-on voltage of the MOS tube. The turn-on voltage of the IRF540 we selected is 4V, and our power supply is 5V, so it can ensure that the MOS tube is fully turned on.

On-resistance: When the MOS tube is fully turned on, there is an impedance between the drain and the source, which is called the on-resistance. This value should be as low as possible, otherwise there will be a large voltage drop, so that there will not be enough voltage to turn on the solenoid valve. The on-resistance of the MOS tube here is only 0.077Ω.

If you want to build other solenoid valve applications, you must read the specification of the MOS tube you selected carefully. The 7805 linear regulator is used to convert the 12V input to 5V. After the switch is pressed, the voltage is transmitted to the gate of the MOS tube through the 1kΩ current limiting resistor. When the switch is not pressed, the gate is pulled down by a 10kΩ resistor. This allows the MOS tube to be turned off when the switch is not pressed. Finally, a diode is connected in reverse parallel to prevent the solenoid valve from discharging to the power supply circuit.

How the solenoid valve drive circuit works

Now that we understand the principle of the drive circuit, let's test the circuit built on the breadboard. I used a 12V adapter as the power supply, and the following is a physical picture.

When the middle button switch is pressed, the +5V voltage supplies the MOS tube to turn it on, thereby opening the solenoid valve. Pressing the switch again will disconnect the +5V power supply, so that the solenoid valve returns to the off state. The switch of the solenoid valve can be judged by the sound it makes. To make it more obvious, we can connect the top of the solenoid valve to a water pipe. In the default state, the solenoid valve is in the off state, so no water flows out. Once the solenoid valve is opened, water will flow into the cup from the bottom.