MOSFET as a power switch in Power Electronics - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the terminal of a MOSFET that controls the switching.

Power Electronics

The terminal that controls the MOSFET switching is called the [1].

Drag options to blanks, or click blank then click option'

ADrain

BSource

CGate

DBody

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing the Drain or Source as the control terminal.

Thinking the Body terminal controls switching.

The Gate terminal controls the MOSFET switching by applying voltage to it.

2fill in blank

medium

Complete the sentence to describe the MOSFET state when the gate voltage is below threshold.

Power Electronics

When the gate voltage is below the threshold voltage, the MOSFET is [1].

Drag options to blanks, or click blank then click option'

Aoff

Bpartially on

Cfully on

Ddamaged

Attempts:

3 left

💡 Hint

Common Mistakes

Assuming the MOSFET is partially on below threshold.

Confusing threshold voltage with maximum voltage.

The MOSFET remains off when the gate voltage is below the threshold voltage, meaning it does not conduct.

3fill in blank

hard

Fix the error in the statement about MOSFET conduction.

Power Electronics

A MOSFET conducts current between the drain and the [1] when it is on.

Drag options to blanks, or click blank then click option'

Abody

Bdrain

Cgate

Dsource

Attempts:

3 left

💡 Hint

Common Mistakes

Thinking current flows through the gate terminal.

Mixing up source and drain terminals.

The MOSFET conducts current between the Drain and Source terminals, not the gate. The gate controls the conduction but does not conduct current.

4fill in blank

hard

Fill both blanks to complete the description of MOSFET switching behavior.

Power Electronics

When the gate voltage is [1] the threshold voltage, the MOSFET switches [2].

Drag options to blanks, or click blank then click option'

Aabove

Bbelow

Con

Doff

Attempts:

3 left

💡 Hint

Common Mistakes

Reversing the relationship between gate voltage and switching state.

Confusing 'on' and 'off' states.

The MOSFET switches on when the gate voltage is above the threshold voltage.

5fill in blank

hard

Fill all three blanks to complete the dictionary comprehension describing MOSFET states.

Power Electronics

mosfet_states = [1]: [2] for [3] in ['gate_voltage', 'threshold_voltage']

Drag options to blanks, or click blank then click option'

A{'state'

B'on' if gate_voltage > threshold_voltage else 'off'

Cgate_voltage

Dstate

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect dictionary syntax.

Confusing keys and values in the comprehension.

Using wrong variable names.

This dictionary comprehension creates a dictionary named mosfet_states with key 'state' and value 'on' or 'off' depending on whether gate_voltage is greater than threshold_voltage.

Practice

1. What happens when a voltage is applied to the Gate of a MOSFET used as a power switch?

easy

A. The MOSFET heats up but does not conduct

B. The MOSFET turns OFF and blocks current

C. The MOSFET turns ON and allows current to flow

D. The MOSFET permanently damages

Solution

1. Step 1: Understand MOSFET Gate control

   Applying voltage to the Gate creates an electric field that allows current flow between Drain and Source.

2. Step 2: Effect on current flow

   When ON, the MOSFET acts like a closed switch, letting current pass through.

3. Final Answer:

   The MOSFET turns ON and allows current to flow -> Option C

4. Quick Check:

   Gate voltage ON = MOSFET ON [OK]

Hint: Gate voltage ON means MOSFET conducts current [OK]

Common Mistakes:

• Confusing ON and OFF states
• Thinking MOSFET heats up to conduct
• Assuming Gate voltage damages MOSFET

2. Which of the following is the correct symbol for an N-channel MOSFET used as a power switch?

easy

A. Arrow on the source leg pointing inward

B. A circle with a diagonal line through it

C. A rectangle with two terminals only

D. Arrow on the source leg pointing outward

Solution

1. Step 1: Identify N-channel MOSFET symbol

   The N-channel MOSFET symbol has an arrow on the source leg pointing inward.

2. Step 2: Compare options

   Arrow on the source leg pointing inward matches this description; arrow on the source leg pointing outward describes a P-channel MOSFET.

3. Final Answer:

   Arrow on the source leg pointing inward -> Option A

4. Quick Check:

   N-channel MOSFET arrow points inward [OK]

Hint: N-channel MOSFET arrow points inward on source [OK]

Common Mistakes:

• Mixing N-channel and P-channel symbols
• Confusing arrow direction
• Choosing symbols with missing terminals

3. Consider a MOSFET used as a power switch with a Gate voltage of 10V applied. What is the expected behavior of the MOSFET?

easy

A. It remains OFF because 10V is too high

B. It permanently damages the MOSFET

C. It oscillates between ON and OFF

D. It turns ON and allows current to flow

Solution

1. Step 1: Check Gate voltage level

   10V is a typical Gate voltage sufficient to fully turn ON a power MOSFET.

2. Step 2: Determine MOSFET state

   With Gate voltage applied, the MOSFET channel forms and current flows freely.

3. Final Answer:

   It turns ON and allows current to flow -> Option D

4. Quick Check:

   Gate voltage 10V = MOSFET ON [OK]

Hint: High Gate voltage turns MOSFET ON [OK]

Common Mistakes:

• Assuming high voltage damages MOSFET instantly
• Thinking MOSFET stays OFF at high voltage
• Confusing oscillation with switching

4. A MOSFET switch circuit is not turning ON even when 5V is applied to the Gate. What could be the likely cause?

medium

A. The MOSFET is a logic-level type

B. The Gate voltage is below the MOSFET's threshold voltage

C. The MOSFET is connected correctly

D. The Source and Drain are shorted

Solution

1. Step 1: Understand threshold voltage concept

   MOSFETs require a minimum Gate voltage (threshold voltage) to turn ON.

2. Step 2: Analyze 5V Gate voltage

   If the MOSFET is not logic-level type, 5V may be insufficient to reach threshold voltage, so it stays OFF.

3. Final Answer:

   The Gate voltage is below the MOSFET's threshold voltage -> Option B

4. Quick Check:

   Gate voltage < threshold = MOSFET OFF [OK]

Hint: Check if Gate voltage exceeds threshold voltage [OK]

Common Mistakes:

• Assuming 5V always turns MOSFET ON
• Ignoring MOSFET type (logic-level or not)
• Overlooking wiring errors

5. You want to use a MOSFET as a power switch to control a 12V motor that draws 5A. Which MOSFET characteristic is most important to ensure efficient switching?

hard

A. Low Drain-Source ON resistance (Rds(on))

B. High Gate threshold voltage

C. High Gate capacitance

D. Low maximum Drain current rating

Solution

1. Step 1: Identify key MOSFET parameter for power loss

   Low Drain-Source ON resistance (Rds(on)) reduces power loss and heat when conducting high current.

2. Step 2: Evaluate options

   High threshold voltage or gate capacitance reduce efficiency; low current rating risks damage.

3. Final Answer:

   Low Drain-Source ON resistance (Rds(on)) -> Option A

4. Quick Check:

   Low Rds(on) = efficient power switching [OK]

Hint: Choose MOSFET with low Rds(on) for power efficiency [OK]

Common Mistakes:

• Selecting MOSFET with high threshold voltage
• Ignoring current rating
• Overlooking gate capacitance effects