What is the difference between a low-side and high-side gate driver?

A low-side driver switches a MOSFET whose source is at ground, so the output simply swings between ground and the supply. A high-side driver switches a MOSFET whose source floats (for example at the switch node of a bridge), so it needs a floating supply, usually made with a bootstrap capacitor and diode.

What is a bootstrap circuit in a gate driver?

A bootstrap circuit is a capacitor and diode that create a floating supply for the high-side output. When the switch node is low, the capacitor charges through the diode from the main supply; when the node swings high, the capacitor floats up with it and powers the high-side gate drive.

What is dead-time in a half-bridge driver?

Dead-time is a short delay during which both the high-side and low-side MOSFETs are off. It stops them from ever conducting at the same time, which would short the supply through both switches, a fault called shoot-through.

Gate Driver IC Explained — MOSFET/IGBT Drive, Bootstrap & Half-Bridge

What is a Gate Driver IC?

A gate driver IC is a fast current buffer and level shifter that sits between a controller (a microcontroller or PWM chip) and the gate of a power MOSFET or IGBT. It delivers the strong, quick pulse of current the gate needs to switch cleanly.

The controller decides when to switch; the gate driver provides the muscle to actually do it fast.

Gate driver IC concept: a weak PWM signal from an MCU is buffered into a strong drive for a power MOSFET gate

Weak PWM in → amps of gate current out. The driver charges/discharges the gate capacitance fast.

1–9 A

Peak gate current

buffer

Current amplifier

level shift

Logic → 10–15 V

fast

ns switching

Why It's Needed

A MOSFET/IGBT gate is essentially a capacitor (its gate charge, Q_g). To switch fast you must move that charge in nanoseconds — which needs a big current pulse a controller simply can't supply.

Why a gate driver is needed: gate charge requires amps of current while a microcontroller can only supply milliamps

Peak current needed = Q_g / t. A MCU pin gives ~20 mA; a driver gives amps.

I_peak = Q_g / t_switch

Example: 50 nC in 50 ns = 1 A. Drive it slowly and the MOSFET spends too long half-on — huge switching loss and heat.

How It Drives the Gate

The driver copies the input PWM but delivers strong, fast edges. The gate voltage V_GS ramps up (its slope set by the gate resistor), pauses at the Miller plateau, then reaches full drive.

Gate drive waveforms: input PWM and the resulting gate-source voltage with a Miller plateau and Rg-controlled slew

Input PWM → a clean V_GS with fast, R_g-shaped edges and the tell-tale Miller plateau.

Low-Side Driver

The simplest case: the MOSFET's source is at ground, so the driver output just swings between 0 and V_CC.

Low-side gate driver switching a MOSFET whose source is connected to ground, with a gate resistor

Low-side: source at ground, output swings 0→V_CC, with R_g to the gate and the load on the drain.

High-Side Driver & Bootstrap

When the MOSFET's source floats (as at a bridge switch node), the driver needs a floating supply above the source. The clever, cheap trick is a bootstrap capacitor and diode.

High-side gate driver with a bootstrap capacitor and diode powering the floating high-side output

C_boot charges via D_boot when the switch node (V_S) is low, then floats up to power the high-side gate.

Keep it switching

A bootstrap supply only recharges when the low side turns on, so a pure high-side switch that stays on forever needs a different supply (charge pump or isolated). For normal PWM it works perfectly.

Half-Bridge Driver

One chip drives both a high-side and a low-side MOSFET — the totem-pole at the heart of every inverter and buck/boost stage.

Half-bridge gate driver controlling a high-side and low-side MOSFET with dead-time

HO and LO drive the two switches; their common node is the output. Built-in dead-time prevents shoot-through.

Shoot-through

If both MOSFETs are ever ON together, the supply is shorted through them — a destructive shoot-through current. Dead-time (a brief both-off gap) is what stops it.

The Gate Resistor (R_g)

A small resistor between the driver and the gate sets the switching speed — and trades it against EMI and ringing.

Gate resistor Rg with a split turn-on and turn-off network using a diode

Small R_g = fast & efficient but noisy; large R_g = clean but lossy. A diode split sets turn-on and turn-off separately.

switching time ≈ R_g × C_iss

Tune R_g to balance efficiency (fast) against EMI, ringing and voltage overshoot (slow).

Isolated Gate Drivers

For high-voltage and mains-connected stages, an isolated gate driver puts a safety barrier between the control side and the power side.

Isolated gate driver using an optocoupler or digital isolator to separate the low-voltage and high-voltage sides

An optocoupler or digital isolator carries the signal across the barrier — essential for IGBT mains drives & safety.

Isolation protects the low-voltage electronics (and the user) from the high-voltage power stage, and breaks ground loops in large systems. It is a must for motor drives, solar inverters and EV power stages.

Key Parameters

Pick a driver by these specs — they decide how fast, how safe and how robust your power stage is.

Peak current, propagation delay, UVLO, dead-time, isolation and Miller clamp.

Gate Driver ICs & Pinout

The IR2110 is the classic high-and-low-side driver; single low-side parts like the TC4420 and UCC27511 are everywhere too.

Functional pinout of the IR2110 half-bridge gate driver with logic-side and high/low-side pins

The IR2110: logic pins (VDD/HIN/LIN/SD/VSS) on one side; high-side (VB/HO/VS) and low-side (VCC/LO/COM) on the other.

IR2110 / IR2104

High + low side (half-bridge), bootstrap, with dead-time (IR2104).

TC4420 / UCC27511

Fast single low-side drivers for one MOSFET.

Si823x / isolated

Reinforced isolation for mains & IGBT drives.

Applications

Wherever power is switched at speed, a gate driver is in the loop.

From SMPS to EV traction — gate drivers make efficient power switching possible.

SMPS

Switching power supplies & adapters.

Motor drives

BLDC and induction inverters.

Solar inverters

Grid-tie and off-grid.

DC-DC

Buck, boost and bridge converters.

Class-D audio

High-efficiency amplifiers.

EV & chargers

Traction and on-board chargers.

Key Terms — Glossary

Term	Meaning
Gate driver IC	Current buffer/level shifter that drives a MOSFET/IGBT gate.
Gate charge (Q_g)	Charge needed to switch the gate; sets the drive current.
Low-side	Drives a switch whose source is at ground.
High-side	Drives a switch whose source floats; needs a floating supply.
Bootstrap	Capacitor + diode that make the floating high-side supply.
Half-bridge	High-side + low-side switches driven together.
Dead-time	Both-off gap that prevents shoot-through.
Shoot-through	Destructive current when both bridge switches are on.
Gate resistor (R_g)	Sets switching speed; trades loss vs EMI/ringing.
UVLO	Under-voltage lockout — disables drive at low supply.
Miller plateau	Flat part of V_GS during switching.

Frequently Asked Questions

Quick, expert answers to the questions people ask most about gate drivers.

What is a gate driver IC?

A chip that takes a weak logic/PWM signal and delivers the strong, fast current pulse needed to switch a power MOSFET or IGBT gate. It is a fast current buffer and level shifter between a controller and the power switch.

Why can a microcontroller not drive a MOSFET directly?

The gate is a capacitor with charge Q_g. Switching fast means moving that charge in nanoseconds, needing amps of peak current, but an MCU pin only gives tens of milliamps — so the MOSFET switches slowly and overheats.

Low-side vs high-side gate driver?

A low-side driver switches a MOSFET with its source at ground (output swings 0→V_CC). A high-side driver switches one whose source floats, so it needs a floating supply, usually a bootstrap capacitor and diode.

What is a bootstrap circuit?

A capacitor and diode that make a floating supply for the high-side output. When the switch node is low, the cap charges through the diode; when the node swings high, the cap floats up and powers the high-side gate.

What is dead-time in a half-bridge?

A short delay when both MOSFETs are off, so they never conduct together and short the supply (shoot-through). Half-bridge drivers add dead-time automatically.

What does the gate resistor Rg do?

It sets switching speed by limiting gate current. Smaller R_g = faster and lower loss but more EMI/ringing; larger = slower and cleaner. A diode split can set turn-on and turn-off speeds separately.

What is an isolated gate driver?

One that carries the signal across an isolation barrier (optocoupler or digital isolator), separating the low-voltage control side from the high-voltage power side. Essential for mains IGBT drives and safety.

What are common gate driver ICs?

IR2110 and IR2104 (half-bridge), TC4420 and UCC27511 (single low-side), and Si823x-family isolated drivers. Choose by peak current, driver type, and whether you need isolation.

Conclusion & Key Takeaways

A gate driver is the essential link that lets a small controller switch big power fast, efficiently and safely.

Current buffer

Amps to charge the gate.

I = Q_g/t

Why an MCU can't.

Low / high-side

Bootstrap for high-side.

Dead-time

No shoot-through.

R_g

Speed vs EMI.

Isolation

Safety at high voltage.

Gate Driver IC

Complete Learning Path — Gate Driver IC