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Project Specification: 5V MOSFET Heater Driver
Overview
A 5 V, 10 W resistive heater driver using a logic-level N-channel MOSFET as a low-side switch. The MOSFET gate is driven from an external MCU DAC/gate-control signal through a series gate resistor, with a pulldown to keep the heater off during MCU reset or high-impedance states.
Requirements
- Input voltage: 5 V DC
- Heater power: 10 W nominal
- Heater current: 2 A nominal
- Control input: MCU DAC/gate-control signal referenced to board GND
- Topology: Low-side N-channel MOSFET switch
- External interfaces: 2-pin power input, 2-pin heater output, MCU control header
Power Budget
Table
| Rail / Path | Load | Nominal Current | Notes |
|---|---|---|---|
| 5V_FUSED | Heater | 2 A | 10 W / 5 V |
| Gate input | MOSFET gate | transient only | Set by gate charge and R1 |
Input protection and connectors are sized above the 2 A nominal load. The selected resettable PTC has 3 A hold current; verify ambient-temperature derating and voltage drop in the final enclosure.
Architecture
- J1 accepts 5 V input.
- F1 protects the input path.
- J2 connects the external resistive heater between fused 5 V and the MOSFET drain switch node.
- Q1 sinks heater current to GND when driven on.
- R1 provides gate damping/current limiting.
- R2 pulls the MOSFET gate low when the MCU output is high impedance.
- C1/C2 provide local bulk and high-frequency bypass capacitance.
Layout Notes
- Route VIN_5V, 5V_FUSED, HEATER_SW, and GND for at least 2 A continuous current, preferably with wide copper pours.
- Place Q1, J2, C1, and C2 close together to minimize switching-loop area.
- Provide thermal copper around Q1 and F1.
- Keep the MCU gate-control trace away from the high-current heater loop where practical.
Open Decisions
- Confirm MCU DAC high-level voltage. Q1 is logic-level and suitable for 3.3 V/5 V gate drive, but analog DAC drive below full logic high will partially enhance the MOSFET and increase heating.
- Confirm whether PWM or linear heater control is intended. For linear control, this MOSFET power/thermal design must be revisited.
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