![]() ![]() The lower voltage is often around -4.5V and shows the resistance if you were to drive it directly off of 5V logic. If there are two voltages listed, the highest voltage will be the voltage at which the device is fully saturated and show the lowest resistance, often -10V. This means a MOSFET driver, transistor or some other means is required to drive the gate with something close to 10V. If it is spec’d at -10V only, the part is not logic compatible and needs something close to 10V to drive it into saturation. The key to look for here is that R DS(on) may be specified at one or a couple of V GS voltages. R DS(on) : Static Drain-to-Source On-Resistance is the minimum resistance of the MOSFET when it is driven to the fully ON state known as the Saturation Region. Any voltage higher than this will drive the MOSFET to the OFF state known as the Cut-Off Region. V GS(th) : Gate Threshold Voltage is the voltage at which the MOSFET starts to conduct. V GS : Gate Voltage is the negative voltage differential between the Gate and the Source which is how hard the MOSFET is being driven. Generally the higher the I D rating of the device compared to the amount of current you need to pass though it, the easier it will be to manage thermals. If you have a device that draws 10A, you need an I D > -10A. Achieving the maximum current through the device assumes that you are driving it fully on and that appropriate heat sinking is applied. this will often be specified under several conditions such as at 25C room temperature and at 100C or similar high operating temperature. I D : Continuous Drain Current is the maximum current that the device can handle. If you’re switching 12V, you need a device with a V DS > -12V and usually you want something with a fair amount of safety margin. V DS : Drain-To-Source Voltage is the maximum voltage that the device can be used to switch. ![]() Note that because the device is typically hooked up with the Source connected to the positive voltage which is opposite of an N-Channel device, many of these are spec’d as a negative voltage or current because of the opposite point of reference. MOSFET spec sheets can look pretty complicated, but for many applications we just need to pay attention to a few key parameters that are explained here. If you want to switch a higher voltage load such as a 12V motor, you will need to use a small transistor, MOSFET driver or similar to switch the gate at the Source voltage of 12V to drive the MOSFET completely off.Īn example of this type of circuit is shown to the right. Typical Logic Level Drive Circuit for 12V Load Example Logic Controlled P-Channel Power MOSFET Circuits When used for switching power to a load, P-Channel MOSFETs are typically used on the high side which means they are placed between the load and the power supply voltage. If using this device with a uC, it is possible to drive the MOSFET gate directly from an digital output pin as shown in the example circuit here.The very low ‘ON’ resistance means that there is very little voltage drop through the device and that also helps to keep power dissipation down. When they are turned OFF (Cut-Off Region), they act as an open circuit much like a mechanical switch would when it is off.įor some applications MOSFETs are also used in their Linear Region where they are are partially conducting, such as for an amplifier, analog fan speed controller or battery charger. They are ideally suited for this because when the MOSFET is turned fully ON (Saturation Region), it has a very low resistance and can pass a lot of current without much power being dissipated in the device similar to a mechanical switch. Power MOSFETs are most often used a switches where they are turned fully ON or OFF to control a load such as a motor or high power LEDs. This is denoted by the schematic symbol with the broken line which indicates that it does not conduct when there is no Gate voltage. Enhancement mode means that when the device has zero Gate voltage relative to the Source, the device is off. MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor which is why we just call it a MOSFET for short. ![]() The NDP6020P is fully 5V and 3.3V logic compatible and is an excellent choice for use with uC.
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