Active Clamp Circuit for Power Converter Switching

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Solution Overview

Problem

High switching frequencies in power converters lead to high rates of change of voltage with respect to time (dV/dt), causing undesirable operations and potential damage due to fast switching times, particularly in circuits using advanced semiconductor technologies like GaN and SiC.

Innovation Solution

The implementation of a clamp circuit with a logic gate and RC networks to provide controlled delays between switching transitions of main and clamp switching devices, ensuring complementary operation and minimizing voltage excursions at the drive terminal, thereby preventing shoot-through events and damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If switching frequency is increased to reduce component size and cost, then operating efficiency and power density are improved, but high dV/dt events cause unintended switch activation and potential damage

Engineering Contradiction:

Improveswitching frequencyVSAvoidswitch safety

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The clamp circuit is activated in advance before the main switching device turns off. The controller detects the switching signal and activates the clamp circuit proactively, so that when high dV/dt events occur during switching transitions, the clamp circuit is already in position to clamp the voltage and prevent unintended activation of other switches.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The clamp circuit acts as an intermediary protective element between the main switching device and other circuit components. It introduces a clamp switching device and clamp capacitor that mediate the voltage transitions, absorbing the harmful dV/dt effects and protecting the main switching device and other circuit elements from damage.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Use of energy by moving object

If switching speed is increased using advanced semiconductor technologies like GaN and SiC, then power conversion efficiency is improved, but high dV/dt rates trigger undesirable operations in other circuits

Engineering Contradiction:

Improvepower conversion efficiencyVSAvoidhigh dV/dt events

Core Design Contradiction:

Use of energy by moving objectVSObject-generated harmful factors

Solution Approach 1:

The clamp circuit converts the harmful high dV/dt events into beneficial voltage clamping action. When the main switching device switches and generates high dV/dt, the clamp circuit detects this and activates to clamp the voltage, transforming the harmful voltage spike into a controlled clamping action that protects other circuit elements while allowing the fast switching to continue.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The clamp circuit applies preliminary anti-action by preparing to counteract the harmful dV/dt effects before they can cause damage. The controller is configured to activate the clamp circuit based on detection of switching signals, so the protective action is already in place or quickly activated when the harmful voltage transitions occur.

Inventive Principle:

Principle #9Preliminary anti-action

3Reliability

If clamp circuit is added to protect against high dV/dt, then switch safety is improved, but circuit complexity increases

Engineering Contradiction:

Improveswitch protectionVSAvoidcircuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The clamp circuit is configured to activate automatically based on detection of the main switching device's operation. The controller detects the switching signal and self-activates the clamp circuit without requiring external control signals or complex control logic, allowing the clamp circuit to protect itself and other devices autonomously.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The clamp circuit shares common components with the main switching circuit, such as using the same controller for detection and control, and sharing power supply connections. This merging of functions and components reduces the overall complexity increase that would result from adding a completely separate protection circuit.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS11545973B2Fast active clamp for power converters

Publication Date: 2023.01.03 APPLE INC

AI summary

A switching system can include a main switching device configured to switch a voltage, a gate driver having an output coupled to a drive terminal of the main switching device and configured to deliver a drive signal to the main switching device, and a clamp circuit. The clamp circuit can be coupled to the drive terminal of the main switching device. The clamp circuit can include a logic gate configured to drive a clamp switching device coupled to and configured to clamp a voltage at the drive terminal of the main switching device. A drive signal of the clamp switching device can be substantially complementary to the main switching device drive signal. The logic gate can provide at least a portion of a delay between switching transitions of the main switching device and switching transitions of the clamp switching device.