High-Side MOSFET Drive: Gate Voltage Must Be Referenced to the Moving Source

Identify the local voltage reference

Analog Devices explains that a high-side switch’s source moves with its output node, so the gate drive must be referenced to that source. Primary reference: high-side gate reference.

A voltage measured against system ground and a voltage between gate and source describe different pairs of nodes. The gate driver’s local supply and return belong to the circuit drawing. A high absolute gate voltage alone does not establish the relevant gate-to-source condition.

A hypothetical node calculation

Imagine a fictional instant when source voltage is 24 V relative to ground and gate voltage is 32 V relative to the same ground. Gate-to-source voltage is 32−24 =8 V. A gate voltage of 12 V with that source condition would instead give −12 V between gate and source.

Neither case specifies permitted operation or a device threshold. Actual gate limits, required conducting behavior and driver architecture must come from the component assessment. These invented node values illustrate why a ground-referenced label can answer the wrong drive question.

Preserve both node histories

List gate, source and reference-node voltages together and derive the local difference. Keep the relevant time interval because the source node may change during switching.

Ask which architecture maintains the intended local supply and what conditions limit it. This guide prescribes no bootstrap component or wiring change. Its worksheet provides a concrete check that a gate-drive proposal retains the correct reference rather than relying on one impressive absolute voltage.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• Primary reference: high-side gate reference