Gate Driver working principle

A gate driver works by moving electrical charge into and out of a transistor gate. On a turn-on command, the pull-up stage sources current and raises the gate voltage. On a turn-off command, the pull-down stage sinks current and returns the gate to its off-state voltage. The gate driver controls the switch; the main load current flows through the power device.

Why gate charge matters

A transistor gate behaves capacitively, but the required charge changes through the switching event. Datasheets therefore specify total gate charge (Qg), Miller charge (Qgd), and a gate-charge curve. During the Miller plateau, drain-source or collector-emitter voltage changes while gate voltage remains comparatively flat.

Driver current in this interval has a strong influence on switching time and switching loss.

First-order estimate:  Average gate current is approximately I ≈ Qg / t. Use this only as a starting point; verify the gate-charge curve, Miller plateau, output resistance, external gate network, temperature, and switching measurements.

Source and sink current paths

Most outputs use a push-pull or totem-pole stage. The source transistor charges the gate and the sink transistor discharges it. Source and sink ratings can differ. A stronger sink path can improve turn-off behavior and immunity to parasitic turn-on. Separate source and sink outputs allow independent turn-on and turn-off resistors without steering diodes.

Gate resistance and switching tradeoffs

The external gate resistor limits peak current and shapes dV/dt and dI/dt. Lower resistance generally reduces switching time and loss but can increase ringing, overshoot, EMI, reverse current, and false turn-on.

Higher resistance softens switching but increases time in the linear region. The optimum value is established with the selected switch, driver, PCB, load, and operating point.

Propagation delay, delay matching, and deadtime

Propagation delay is the interval from an input transition to the corresponding output transition. Bridge designs must also consider channel-to-channel, rise-to-fall, and part-to-part variation. Deadtime prevents complementary switches from conducting simultaneously. Too little deadtime creates shoot-through risk; too much increases diode or reverse-conduction loss.

How a bootstrap circuit powers the high-side channel

A bootstrap diode and capacitor create a supply that floats with the high-side switch node. When the node is low, the capacitor charges from the fixed supply. When the high-side switch turns on, the charged capacitor rises with the switch node and powers the floating output stage. Leakage, quiescent current, gate charge, switching frequency, duty cycle, and maximum on-time determine the capacitor and diode requirements.

Bootstrap limit:  A conventional bootstrap needs periodic refresh and normally cannot sustain indefinite 100% high-side duty cycle. A charge pump, isolated bias supply, or another charging path may be required.

Next step: Explore Half-bridge Gate Drivers and High-side Gate Drivers

Compare devices with integrated bootstrap diodes, active bootstrap functions, charge pumps, UVLO, and deadtime options.

How isolation transfers the command

An isolated driver transfers switching information across an insulation barrier while keeping the input and output electrical domains separated. The output stage still needs local bias power. The barrier, package, creepage, clearance, working voltage, surge capability, certification, and CMTI must all be evaluated; a single isolation test-voltage number is not sufficient.

Next step: Explore isolated gate driver ICs

Review Coreless Transformer-based isolated families and available functional, basic, or reinforced isolation options.

How protection functions respond

Next step: Compare Gate Driver protection features

See detailed explanations of DESAT, Miller clamp, soft-off, TLTO, UVLO, OCP, bootstrap, and diagnostics.

Practical validation sequence

  • Use the switch datasheet to define gate voltage, Qg/Qgd, threshold, and short-circuit constraints.
  • Choose the topology and decide between common-reference, level-shift, and galvanically isolated drive.
  • Estimate current and tune gate resistance using the real switching loop.
  • Check delay, matching, pulse width, deadtime, CMTI, negative-transient behavior, and startup sequencing.
  • Verify fault detection and controlled turn-off at worst-case voltage, current, temperature, and tolerances.
  • Perform double-pulse and application-level tests before release.

Next step: Evaluate with the modular platform

Pair selected isolated drivers and power switches and perform switching tests, including double-pulse evaluation.

Explore the Gate Driver ICs catalogue

Recommended documents

Frequently asked questions about how Gate Drivers work

How does a Gate Driver turn a MOSFET on? 

It sources current into the gate until the required gate-source voltage and gate charge are reached. The MOSFET then conducts according to its operating conditions. 

It is the portion of the gate-charge transition during which the gate voltage changes little while the drain-source voltage, collector-emitter voltage, or switch-node voltage changes substantially. Driver current during this interval affects switching speed and loss. 

Turn-on and turn-off have different system priorities. A stronger sink current can provide faster turn-off and better immunity to unwanted or parasitic turn-on. 

Use gate charge (Qg) divided by the target switching or transition time as a first estimate. Then account for the driver output resistance, external gate network, supply voltage, Miller plateau behavior, switching frequency, and thermal limits. 

It charges the bootstrap capacitor when the switch node is low and blocks reverse current when the high-side node rises.

Not indefinitely with a conventional bootstrap supply alone, because the bootstrap capacitor requires a refresh interval. Check the driver architecture and the application's duty-cycle requirements. 

It reduces timing uncertainty between channels or devices, allowing deadtime to be set more accurately. 

Common-mode transient immunity indicates how well an isolated or level-shift gate driver maintains correct operation during fast voltage changes between its reference domains. 

Switching can become very fast, increasing ringing, overshoot, electromagnetic interference (EMI), reverse current, or false turn-on. The optimum resistance is system-dependent. 

Depending on the device, the driver detects desaturation (DESAT) or overcurrent, reports the fault, and turns the switch off using soft-off, two-level turn-off (TLTO), shutdown, or another controlled strategy.