|
|
|
|
|
|
Datasheets : Solenoid -Output Device
What does it do?
|
|
Click on the circuit diagram to download a Livewire file of the circuit that you can investigate and add to your own circuit. |
Solenoids come in a variety of voltages and currents. The power supply for the solenoid (which can be separate from the supply for the rest of the electronics) must provide the voltage needed by the solenoid. The driver providing the input signal must be able to provide a larger current than the specified current for the solenoid. Solenoids also come in a variety of sizes and fittings. The solenoid is connected between the supply rail (+Vs) and the input signal from the driver. This acts as a load on the driver. When the input signal coming into the solenoid subsystem is low, a potential difference across the solenoid causes current to flow through a magnetic coil. It is the magnetic field caused by this current that causes the rod of the solenoid to move. The reverse biased diode is included because, when solenoids are switched off, they can generate a ‘back e.m.f.’ that can damage the driver. When the solenoid is switched off the diode conducts current and prevents the damage. |
|
|
Usually the rod of a solenoid is moved in when the driver is on and pushed out (by a spring) when it is off. This wastes electrical energy because electrical energy has to be continuously applied to keep the rod in. Latching solenoids are available. These move in when a short pulse of current is passed. They move back out when a second pulse is passed. In this way energy is saved because, once the rod has been moved in by the short pulse, no further electrical energy is needed. |
Solenoids only provide quite a weak force and a short movement.
Normally a solenoid would not be mounted on the PCB. (PCB-mounted solenoids are available, but they are more difficult to link to the other mechanical parts.) Usually a terminal block is mounted on the PCB and wires from this are connected to the solenoid.
A PCB-mounting terminal block
Build and test the unit that will provide the driving input signal before adding the solenoid.
Make sure that the solenoid moves in and out as power is applied from the driver unit.
If there is a fault, check the solenoid by removing it from the circuit and applying power to it directly. Check the voltage at the terminals of the terminal block.
