DC/DC Converter Depletion Mode Switch Power Up Safety

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Solution Overview

Problem

III-nitride based switches in DC/DC converters are normally on by default, posing risks of short circuits due to power up sequence issues and pre-bias conditions, which existing technologies fail to adequately address.

Innovation Solution

Incorporating an enhancement mode switch to selectively enable or cut off current to the III-nitride depletion mode switch, using a silicon-based enable switch or cutoff switch to manage power up sequences and prevent pre-bias damage, with configurations for both high side and low side III-nitride switches.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If III-nitride depletion mode switches are used in DC/DC converters, then current capacity and voltage withstand ability are improved, but the risk of short circuits increases due to normally-on characteristic during power up sequence issues and pre-bias conditions

Engineering Contradiction:

Improvevoltage withstand abilityVSAvoidshort circuit risk

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

An enhancement mode switch is introduced as an intermediary component between the power source and the III-nitride depletion mode switch. This intermediary switch controls the gate voltage of the depletion mode switch, enabling it to be turned off during power-up and pre-bias conditions, thereby preventing short circuits while maintaining the high voltage withstand ability of the III-nitride device.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The enhancement mode switch performs preliminary action by pre-charging the gate of the III-nitride depletion mode switch to a voltage below its threshold voltage before main operation begins. This preliminary action ensures the depletion mode switch remains off during critical power-up sequences, eliminating short circuit risks before they can occur.

Inventive Principle:

Principle #10Preliminary action

2Loss of energy

If III-nitride depletion mode switches are used, then parasitic capacitances are reduced, but device complexity increases due to the need for additional enhancement mode switches and control circuitry

Engineering Contradiction:

Improveparasitic capacitanceVSAvoidswitch configuration

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The enhancement mode switch serves multiple functions: it acts as a protective device during power-up, a control element for the depletion mode switch, and a means to manage pre-bias conditions. By making the enhancement mode switch multi-functional, the patent reduces the need for separate control circuits, thereby limiting the increase in device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If enhancement mode switches are added to control III-nitride switches, then safety during power up sequences is improved, but manufacturing cost increases

Engineering Contradiction:

Improvepower up safetyVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The enhancement mode switch is designed as a simpler, lower-cost component compared to the III-nitride depletion mode switch. By using a less expensive enhancement mode switch (which can be silicon-based) to control the expensive III-nitride device, the patent protects the high-value component while accepting the addition of a lower-cost component, thereby limiting the overall manufacturing cost increase.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Data Source

PatentUS7902809B2DC/DC converter including a depletion mode power switch

Publication Date: 2011.03.08 INFINEON TECHNOLOGIES AMERICAS CORP

AI summary

A buck converter circuit is disclosed in which one or both of the control switch and the synchronous switch are III-nitride-based depletion mode. An enhancement mode switch is connected with one or both of the III-nitride based switches and operated to prevent conduction of current by the III-nitride based switch until all biases are established for proper operation.