Introduction to Arduino Half Bridge Circuits
Building an Arduino half bridge is a rite of passage for makers moving beyond simple relays and motor driver shields. A half-bridge circuit consists of two power switches (typically N-channel MOSFETs) arranged in series between a high-voltage supply and ground. The load is connected to the midpoint. This topology is the foundational building block for DC motor direction control (where two half-bridges form an H-bridge), high-power buck converters, and induction heaters.
However, bridging the gap between the Arduino's 5V/3.3V low-current logic and the high-voltage, high-current demands of power MOSFETs requires precise engineering. This quick reference FAQ addresses the most common design hurdles, component selections, and failure modes encountered in 2026 maker projects.
Quick Reference: Top Gate Drivers for Arduino
You cannot drive a half-bridge directly from an Arduino GPIO pin. You need a dedicated gate driver to supply the peak current required to charge the MOSFET gate capacitance in nanoseconds. Below is a comparison of the most reliable gate drivers for Arduino-based half-bridge designs.
| Driver IC | Max Voltage | Typical Price (2026) | Key Features & Arduino Compatibility |
|---|---|---|---|
| IR2104 | 600V | $1.20 - $1.80 | Classic half-bridge driver. Requires PWM and a direction/enable pin. Built-in 520ns dead-time prevents shoot-through. Ideal for basic motor control. |
| DRV8701 (TI) | 47V | $3.50 - $4.50 | Smart gate driver with SPI/I2C control. Features adjustable dead-time, current sensing, and a charge pump for 100% duty cycle support. Best for advanced robotics. |
| HIP4081A | 80V | $3.00 - $5.00 | Technically a full H-bridge driver, but frequently used to drive robust dual half-bridges. Excellent built-in dead-time and high peak gate current (up to 2.5A). |
| IR2110 | 500V | $2.50 - $3.50 | Independent high/low side inputs. Requires the Arduino to generate precise dead-time in software or via external logic gates. Not recommended for beginners. |
Frequently Asked Questions (FAQ)
1. Why can't I connect Arduino PWM pins directly to power MOSFETs?
Many beginners attempt to wire an Arduino PWM pin directly to the gate of a power MOSFET like the IRF540N. While the Arduino can technically output 5V, it can only source about 20mA of continuous current. Power MOSFETs have a parasitic capacitance called Gate Charge (Qg). To switch a MOSFET efficiently at high frequencies (e.g., 20kHz), you must charge and discharge this gate capacitance in a matter of nanoseconds. This requires peak currents of 1A to 3A.
If you rely on the Arduino's weak 20mA output, the MOSFET will spend too much time lingering in the 'Miller Plateau' (the linear region where it acts as a resistor rather than a switch). This causes massive power dissipation, leading to instant thermal runaway and a melted MOSFET. A gate driver acts as a current amplifier, taking the Arduino's weak signal and blasting the gate with the amps needed for crisp, nanosecond switching.
2. What is a bootstrap circuit and why does my high-side MOSFET overheat?
In a half-bridge using N-channel MOSFETs, the low-side MOSFET is easy to drive because its source is tied to ground. The high-side MOSFET, however, has its source connected to the load. When the high-side turns on, its source voltage rises to near the supply voltage (e.g., 24V). To keep it turned on, the gate voltage must be 10V to 15V higher than the source (meaning the gate needs 34V to 39V).
A bootstrap circuit solves this using a fast recovery diode (like the UF4007) and a bootstrap capacitor (typically 0.47µF to 1µF). When the low-side MOSFET turns on, it pulls the midpoint to ground, allowing the supply voltage to charge the bootstrap capacitor. When the high-side turns on, the capacitor acts as a floating battery to power the high-side gate driver.
Critical Warning: Never use an electrolytic capacitor for the bootstrap cap. The high dV/dt (voltage change over time) will destroy it. Always use a low-ESR X7R ceramic capacitor. Furthermore, standard bootstrap circuits cannot support a 100% duty cycle; the capacitor will eventually starve and the high-side MOSFET will overheat. If you need 100% duty cycle, use a driver with an integrated charge pump like the TI DRV8701.
3. How do I prevent shoot-through and blown MOSFETs?
Shoot-through occurs when both the high-side and low-side MOSFETs are turned on simultaneously, even for a microsecond. This creates a dead short from your power supply to ground, resulting in an explosive failure of the MOSFETs. Shoot-through usually happens during the switching transition due to the MOSFETs' turn-off delay times.
To prevent this, you must implement dead-time—a brief period where both MOSFETs are guaranteed to be OFF. The IR2104 handles this internally with a factory-set 520ns dead-time. If you are using a driver without internal dead-time (like the IR2110), you must implement it in hardware using RC delay networks on the gate signals, or via external logic gates. Relying solely on Arduino software delays (e.g., delayMicroseconds(1)) is highly discouraged, as interrupt jitter from timers or serial communications can collapse the dead-time and cause a catastrophic short.
4. Logic-Level vs. Standard MOSFETs: Which should I buy?
When selecting the switching elements for your Arduino half bridge, the part number prefix matters immensely. Standard MOSFETs like the IRFZ44N require a Gate-to-Source voltage (Vgs) of 10V to fully enhance and achieve their advertised low Rds(on) (on-resistance). If driven at 5V, their resistance remains high, causing severe heating.
For direct interfacing with 5V logic (or when using a gate driver powered by a 5V regulator), you must use Logic-Level MOSFETs, denoted by the 'L' in the prefix, such as the IRLZ44N. These are fully enhanced at Vgs = 4.5V or 5V. Always check the datasheet's Rds(on) vs. Vgs graph before purchasing. For modern 2026 builds, consider newer trench MOSFETs like the CSD18540Q5B from TI, which offer vastly superior switching characteristics and lower gate charge than legacy 1990s-era IRF/IRL parts.
Troubleshooting Matrix: Common Half-Bridge Failures
| Symptom | Probable Cause | Actionable Fix |
|---|---|---|
| Arduino resets or freezes when the load engages. | Ground Bounce: High di/dt switching currents are injecting noise into the Arduino's ground reference. | Implement 'star grounding'. Connect the Arduino ground, gate driver ground, and power supply ground at a single physical point. Add a 100µF bulk capacitor and a 0.1µF ceramic bypass cap directly at the half-bridge power pins. |
| High-side MOSFET gets hot instantly, even with no load. | Bootstrap Starvation: The PWM frequency is too low, or duty cycle is too high, starving the bootstrap cap. | Ensure PWM frequency is at least 1kHz to allow the cap to recharge. Verify the bootstrap diode is a fast-recovery type (UF4007), not a slow 1N4007. |
| Low-side MOSFET blows up violently. | Inductive Kickback: Missing or inadequate freewheeling diodes across the load. | Add a Schottky diode (e.g., MBR20100CT) across the load. Do not rely on the MOSFET's internal body diode, as its reverse recovery time (trr) is too slow for high-frequency PWM. |
| Gate driver IC overheats or outputs erratic signals. | Missing Gate Resistors: Parasitic inductance in PCB traces is causing high-frequency ringing on the gate. | Solder a 10Ω to 33Ω carbon film resistor as close to the MOSFET gate pin as possible to dampen ringing. Add a 10kΩ pull-down resistor from gate to source to ensure it stays off during Arduino boot-up. |
Authoritative Resources & Further Reading
To deepen your understanding of power electronics and microcontroller integration, consult the following industry-standard resources:
- Texas Instruments Gate Driver Tutorials - An excellent video series and accompanying whitepapers detailing bootstrap design, dead-time calculations, and smart gate driver architectures.
- Arduino Official PWM Documentation - Essential reading for understanding how Arduino timers generate PWM, including the prescaler settings required to achieve the 16kHz+ frequencies needed for silent motor control and efficient gate driving.
- Infineon Power MOSFET Fundamentals - Comprehensive application notes covering MOSFET parasitics, the Miller effect, and thermal management strategies for high-current switching topologies.
By respecting the physics of gate charge, implementing robust dead-time, and selecting the correct logic-level components, your Arduino half bridge projects will transition from fragile breadboard experiments to reliable, high-power systems capable of driving heavy motors and complex inductive loads.
