NMOS (N-Metal-Oxide-Semiconductor) is a type of MOSFET. Its advantages are low on-resistance and easy manufacturing. When Vgs is greater than a certain value, it will be turned on. It is suitable for the situation when the source is grounded (low-side drive), as long as the gate voltage reaches 4V or 10V. The usual part numbers of Nmos are 2N7002, IRLML2803TRPBF, IRLML5203, etc.
How to understand the working principle of Nmos? For example, when we use Arduino or single-chip microcomputer instead of manually controlling the opening and closing of the switch tube to control the lamp, it will need a Nmos,which has three pins, G, D, S. To control the bulb, you need to connect the Arduino to the G port. When the output of the MCU's IO port is HIGH, Nmos is equivalent to a closed switch, and when the output is LOW, it is equivalent to the switch being opened. If you keep switching the switch, the light will flicker, but when the switching speed is too fast, the light will not flicker in visual. When you adjust the switch time, you can control the brightness of the light, that is PWM dimming.
How to select a Nmos? The following parameters should be considered:
Package: There are many types and appearances of Nmos, such as SOT-23, SOT-89, TO-220, TO-252, SOP-8. Generally, the larger the package, the larger the current it can withstand.
Vgsth: The gs voltage required to turn on Nmos, which should be less than the high-level voltage value. We can think of nmos as a resistance controlled by voltage. The voltage is the voltage difference between GS and the resistance is the resistance between DS. They are not in a linear relationship. When the voltage reaches a certain value, the resistance is infinite, while the voltage is greater than a certain value, the resistance is close to zero.
Rdson: The resistance value when nmos is turned on, that is, the resistance value between DS mentioned earlier. The smaller the value is, not only the partial pressure is less, but the heat is relatively low. However, the corresponding volume will generally be larger.
Cgs: The parasitic capacitance between GS will affect the opening speed of Nmos. Generally, the smaller the Rdson, the larger the Cgs value.
What are the applications of NMos? If you understand the working principle of Nmos, you will find that it is widely used in our lives, and interesting applications can be realized through Nmos in different fields, such as the automatic shooting device used by photographers when taking personalized photos, and the slow dance electronic photo frame that bring you a illusion of slowing movement.