Auxiliary Switch Timing for Power Stage Ringing Reduction

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Solution Overview

Problem

Switch-mode power supplies experience ringing at the switch node, leading to oscillation voltage applied to switches and loads, which can cause breakdown and reduce power efficiency, reliability, and increase electromagnetic interference.

Innovation Solution

Incorporating an auxiliary power switch with higher on-resistance in parallel with a high-side switch, and configuring the gate drive engine to turn on the auxiliary switch earlier than the high-side switch, reducing or eliminating ringing through leading edge blanking of PWM signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If switch-mode power supplies use switching devices with very low resistance when on and very high resistance when off, then high efficiency is achieved, but ringing occurs at the switch node causing oscillation voltage that can lead to breakdown and reduced reliability

Engineering Contradiction:

Improvepower efficiencyVSAvoidswitch reliability

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The auxiliary power switch is turned on a predetermined time duration earlier than the high-side switch before the main switching event. This preliminary action pre-charges the switch node through the auxiliary switch's on-resistance, reducing the voltage oscillation and ringing that occurs when the high-side switch turns on, thereby preventing breakdown while maintaining overall power efficiency

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The auxiliary power switch acts as an intermediary element between the power source and the main high-side switch. By providing a controlled resistance path during the transition period, it mediates the harsh switching transient, reducing electromagnetic interference and protecting the main switch from voltage spikes without significantly impacting the overall power conversion efficiency

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If the auxiliary power switch is turned on earlier than the high-side switch, then ringing at the switch node is reduced or eliminated, but power dissipation during the transition period increases

Engineering Contradiction:

Improveringing reductionVSAvoidpower dissipation

Core Design Contradiction:

Object-affected harmful factorsVSLoss of energy

Solution Approach 1:

The auxiliary power switch is activated only for a predetermined time duration before the main switch turns on, providing just enough pre-charging to reduce ringing without excessive activation. This partial action approach minimizes the time the auxiliary switch conducts, thereby limiting additional power dissipation while still achieving the beneficial ringing reduction effect

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The gate drive engine dynamically controls the timing and duration of the auxiliary switch activation by adjusting the gate drive signal parameters. By optimizing the predetermined time duration and gate voltage levels, the system achieves effective ringing suppression while minimizing the power dissipation penalty during the transition period

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If the auxiliary power switch has higher on-resistance than the high-side switch, then ringing is reduced, but the auxiliary switch consumes more power during operation

Engineering Contradiction:

Improveswitch node oscillationVSAvoidauxiliary switch power consumption

Core Design Contradiction:

Object-affected harmful factorsVSUse of energy by moving object

Solution Approach 1:

The auxiliary power switch with higher on-resistance is activated only temporarily before the main switch turns on, providing preliminary pre-charging to reduce switch node oscillation. The higher resistance is acceptable because the switch operates briefly, minimizing total energy consumption while effectively suppressing ringing during the critical transition period

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS11031922B1Switch circuit with reduced switch node ringing

Publication Date: 2021.06.08 ALPHA & OMEGA SEMICONDUCTOR (CAYMAN) LTD

AI summary

Apparatus and associated methods relate to providing a power stage having an auxiliary power switch coupled to a high-side switch or a low-side switch in parallel and turning on the auxiliary power switch earlier than turning on the high-side switch. In an illustrative example, the auxiliary power switch may be connected with the high-side switch in parallel. The on-resistance of the auxiliary power switch may be greater than the on-resistance of the high-side switch. A gate drive engine may be configured to generate gate driving signals for the switches in the power stage such that the auxiliary power switch is turned on a predetermined time duration earlier than the high-side switch. Thus, the ringing at a switch node of the power stage may be advantageously reduced or eliminated.