What does it do?
| The MOSFET driver subsystem is an electronic switch that provides an output signal powerful enough to drive output subsystems requiring very high current. |
 |
How does it operate?
|
Click on the circuit diagram to download a Livewire file of the circuit that you can investigate and add to your own circuit. |
MOSFET is short for Metal Oxide Semiconductor Field Effect Transistor.
The subsystem acts as an inverter; the output signal is the inverse of the input signal.
The MOSFET has three legs known as the gate, drain and source.
A MOSFET is controlled by the voltage on its gate – about 2V is needed to turn it on. It requires only a tiny gate current to operate – it has a very large ‘input resistance’. |
|
The output subsystem is connect between the supply rail (+Vs) and the output signal from the MOSFET. The output subsystem is sometimes called the load resistance.
As examples of typical MOSFETs, the BS170 MOSFET can provide up to 0.4A for a load. The ZVN 4306A can provide up to 1.1A. The VNP10N06 has built-in protection against overheating, a Schmitt triggered input signal and can provide up to 10A.
The resistor R1 is included to help with testing – it pulls the output signal up to Vs when the MOSFET is off. |
Possible applications
- Providing enough current to drive an output device that needs a relatively high current, such as a motor or solenoid.
Making
When using a MOSFET it is important to be clear about which pin is the drain (D), which is the gate (G) (the equivalent pin is labelled ‘Input’ in the VNP10N06) and which is the source (S). The drain in connected to the load, the gate to the input signal and the source to 0V.
Manufacturer’s data sheets usually show the pins viewed from underneath (unlike IC pins, where the view shown is from above).
Build and test the unit that will provide the input signal before building the MOSFET.
Testing
Make sure that the signal going out (on the green PCB track) is the inverse of the input signal (on the blue PCB track).
Fault finding
If there is a fault, check that the MOSFET is connected the right way round. Then check the resistor value. Check the tracks and solder joints.
Alternatives
- Transistor – cheaper but provides less current
- Darlington Driver – usually cheaper than the MOSFET but cannot provide such a large current
- The L293D driver can drive high current output devices and reverse two motors but is more expensive.
Web links
Return to list of datasheets
