P-Channel MOSFET for High-Side Power Switch

Question

Problem: P-Channel MOSFET for High-Side Power Switch. Solve this hands-on electronics task on EWskills.

Accepted Answer

1. Component Purpose

The MCU needs to switch 5V power to a peripheral module. A P-Channel MOSFET as a high-side switch is ideal for this: source connects to 5V, drain connects to the module, and the gate is controlled by the MCU.

The logic is inverted compared to N-Channel: when the MCU GPIO goes LOW, Vgs becomes -5V (gate is at 0V, source is at 5V), turning the MOSFET ON. When GPIO goes HIGH (3.3V), Vgs = 3.3V - 5V = -1.7V, which is below the threshold, turning the MOSFET OFF.

Required: P-Channel · Vdss ≥12V · Id ≥1A · Vgs(th) ≤2.5V · Rds(on) ≤300mΩ · SOT-23 · SMD

2. How to Find It on DigiKey

Go to DigiKey.com → Discrete Semiconductor Products → Transistors - FETs, MOSFETs - Single

Apply these filters:

FET Type → P-Channel
Technology → MOSFET (Metal Oxide)
Drain to Source Voltage (Vdss) → 12V or higher
Current - Continuous Drain (Id) → 1A or higher
Vgs(th) (Max) → 2.5V or lower
Rds On (Max) → 300mΩ or lower
Package / Case → SOT-23-3 (TO-236)
Part Status → Active

Tip: For P-Channel MOSFETs, DigiKey shows Vgs(th) as an absolute value (e.g., 1.5V) even though the actual threshold is negative (−1.5V). Filter using the absolute value as shown.

3. Key Specifications & What They Mean

Specification	Required	Why
FET Type	P-Channel	High-side switch; source to supply, drain to load.
Vdss	≥12V	Must block 5V supply; 12V gives margin.
Id	≥1A	Module draws 300mA; ~3× margin.
Vgs(th) Max	≤2.5V	Ensures full ON with 5V Vgs (GPIO LOW).
Rds(on)	≤300mΩ	Low drop: 0.3Ω × 0.3A = 90mV loss.
Vgs Max	≥8V	Gate tolerates 5V drive safely.
Power	≥300mW	Covers worst-case dissipation with margin.
Package	SOT-23-3	Compact SMD.
Temp Range	−55°C to +150°C	Standard MOSFET range.
RoHS	Yes	Compliance required.

Important: When the MCU GPIO outputs 3.3V (HIGH), Vgs = 3.3 − 5 = −1.7V. This must be below the threshold for the MOSFET to fully turn OFF. With Vgs(th) ≤2.5V (meaning the FET starts turning ON at −2.5V), a −1.7V Vgs is safely below threshold and the FET stays OFF.

4. Selecting a Safe, Production-Ready Part

The filtered list will show matching parts. Before you pick one, check: Is it Active? Is stock available? Is the manufacturer reputable? Is a datasheet available?

Full checklist: How to Select a Safe, Production-Ready Component — EWskills Guide

5. Filtered DigiKey Link

➡ View Matching Parts — P-Ch MOSFET, SOT-23, Vgs(th)≤2.5V, Id≥1A, Rds(on)≤300mΩ

75. P-Channel MOSFET for High-Side Power Switch