The most common way to connect a solenoid valve to a power supply is to use a suitable valve plug according to the connection diagram EN 175301-803 or similar. These valve plugs are available without any electrical circuits, but also with additional electronics. The tasks of these integrated electronics are, for example, a visual display of the operating status in form of an LED or the protection of the coil of the solenoid valve and the electronics that control the valve.
In order to ensure this protection, the integrated electronics in the valve can be realized in different ways. The effect of such a protective circuit can be explained using the following figure.
Without protective circuit
Without any protective circuit, voltage pulses caused by the coil of the solenoid valve reach the control electronics unhindered. There is therefore no protection against voltage pulses caused by the switching of the magnetic coil.
With freewheeling diode
A freewheeling diode can be used to effectively prevent voltage pulses that are dangerous for the electronics from reaching it. With this variant, you must pay attention to the polarity of the power supply.
With overvoltage protection
On one hand overvoltage protection prevents voltage pulses caused by the magnetic coil and on the other hand the danger of overvoltage caused on the control side. In practice such overvoltage protection is implemented with a voltage depended resistor (VDR) or a TVS diode.
Similar to the circuit with a freewheeling diode, there is also protection against voltage pulses caused by the magnetic coil in a circuit with a rectifier.
The following connector variants are available at SVS-Automation. The plug with overvoltage protection with varistors or TVS diodes also has circuitry with LEDs to display the operating status. The rectifier connector includes an overvoltage conductor for extra protection.