02 MOSFET - Exercícios de chaveamento de mosfet

Summary

This video provides an in-depth look at the switching behavior of N-channel MOSFETs, particularly focusing on how they operate in cutoff and saturation regions. Through three practical examples, the video explains how to calculate drain currents, gate voltages, and average voltages in circuits with resistors. The tutorial also covers the use of Pulse Width Modulation (PWM) to control power dissipation in resistive loads and motor speeds by adjusting the duty cycle. With clear explanations, this video simplifies complex concepts in MOSFET operation, making it accessible to anyone looking to understand electronic switching and power control.

Takeaways

• 😀 The script focuses on the switching of N-channel MOSFETs in electronic circuits.
• 😀 It explains the operation of MOSFETs in both cutoff and on states.
• 😀 In the first example, when the MOSFET gate is at 0V, no current flows due to the absence of a conductive channel.
• 😀 In the second example, a 10V source is used, and the current flowing through two resistors is calculated as 91 microamperes.
• 😀 The script discusses calculating the gate voltage (Vgs) and concludes that it is 9.1V when the MOSFET is fully on.
• 😀 When the MOSFET is fully on, the drain current is determined by the supply voltage divided by the load resistance.
• 😀 The third example introduces the concept of controlling power dissipation in a resistor connected to a MOSFET with a switching signal.
• 😀 The signal alternates between being on for 50% of the time and off for 50%, which controls the average output voltage and dissipated power.
• 😀 The average output voltage is determined by the duty cycle of the switching signal, and this can be calculated using the time the MOSFET stays on.
• 😀 Power dissipation in the resistor is calculated using the average voltage squared, divided by the resistance.
• 😀 The script highlights the practical applications of controlling the MOSFET's on/off cycle to adjust heat dissipation or control the speed of motors using pulse-width modulation (PWM).

Q & A

What is the main topic of the lecture in the script?

The main topic of the lecture is about MOSFET switching, specifically focusing on the operation of an N-channel MOSFET in the cut-off and saturation regions.

What is the significance of the gate voltage in a MOSFET?

The gate voltage controls the formation of the conducting channel in the MOSFET. If the gate voltage is zero, there is no channel formed, and no current flows. When the gate voltage reaches a certain threshold, the channel conducts, and current can flow from drain to source.

How do you calculate the drain current in a MOSFET circuit?

In the example provided, the drain current can be calculated using the formula I = V/R, where V is the applied voltage (10V) and R is the resistance (100 ohms). The resulting current is approximately 91 microamperes.

What happens to the drain current when the MOSFET is fully on?

When the MOSFET is fully on, it behaves like a short circuit, and the drain current reaches its maximum value determined by the supply voltage and the load resistance.

What is the role of the resistors in the MOSFET switching circuit?

The resistors are used to limit the current flowing through the circuit, including the gate and drain currents. They help in determining the operating point of the MOSFET and the behavior of the circuit.

How can the power dissipated in a load resistor be controlled using MOSFET switching?

By adjusting the duty cycle (the percentage of time the MOSFET is on versus off), the average voltage applied to the load resistor can be controlled, thus controlling the power dissipated in the load.

What is the effect of changing the duty cycle on the output voltage?

Changing the duty cycle affects the average output voltage. For example, a 50% duty cycle results in an average output voltage that is approximately half of the supply voltage.

What is the significance of Pulse Width Modulation (PWM) in controlling MOSFETs?

PWM is used to control the width of the pulses applied to the MOSFET. By adjusting the pulse width, the power delivered to the load (e.g., a motor or resistor) can be varied, allowing for control over parameters like speed or heating.

How does the voltage across the load resistor change when the MOSFET is on versus when it is off?

When the MOSFET is on, the voltage across the load resistor is approximately equal to the supply voltage. When the MOSFET is off, no current flows, and thus the voltage drop across the load resistor is zero.

How can the speed of a motor be controlled using a MOSFET?

The speed of a motor can be controlled by adjusting the duty cycle of the PWM signal applied to the MOSFET. A higher duty cycle allows the motor to run faster, while a lower duty cycle slows it down.