GaN Half-Bridge Deadtime Optimization via Drain Current Bump Filter
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Solution Overview
Problem
Conventional methods for deadtime optimization in GaN half-bridge and full-bridge switch topologies are inadequate, as they require auxiliary winding voltage sensing, dedicated pins, and dV/dt detectors that are not applicable to GaN devices, leading to inefficiencies and cross-conduction issues.
Innovation Solution
A method and circuit that utilize a drain current bump filter to generate a current charge output during voltage commutation, comparing it to a reference current charge to adjust deadtime, minimizing losses and avoiding cross-conduction by optimizing deadtime based on the difference between the two signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deadtime is increased to avoid cross-conduction, then reliability is improved, but deadtime losses increase reducing efficiency
Solution Approach 1:
The patent implements dynamic deadtime adjustment by continuously monitoring the current charge output during voltage commutation and comparing it to the reference Coss charge. The deadtime is adjusted in real-time based on the measured current characteristics, allowing the system to maintain minimum necessary deadtime while preventing cross-conduction. This dynamic approach replaces fixed deadtime values with adaptive control that responds to actual device conditions.
Solution Approach 2:
The patent employs feedback control by measuring the actual current charge during voltage commutation, comparing it to the reference Coss charge, and using this comparison to adjust the deadtime. The feedback loop continuously monitors the relationship between measured current charge and expected Coss charge, automatically correcting deadtime settings to prevent cross-conduction while minimizing losses. This closed-loop control ensures optimal performance under varying operating conditions.
2Measurement precision
If conventional dV/dt detectors are used for deadtime control, then deadtime optimization is achieved, but they are not applicable to GaN devices due to different dV/dt characteristics
Solution Approach 1:
The patent changes the measurement parameter from voltage-based dV/dt detection to current-based charge integration. Instead of measuring voltage transitions that differ between Si MOSFET and GaN HEMT devices, the system integrates the drain current during voltage commutation to measure the charge required to charge the output capacitance Coss. This parameter change makes the measurement method universally applicable to both Si and GaN devices while maintaining accuracy.
Solution Approach 2:
The patent substitutes the voltage-based detection mechanism with a current-based integration mechanism. Rather than using dV/dt detectors that sense voltage transitions, the system uses current sensing and integration to measure the charge flow during commutation. This substitution replaces a mechanism that is device-specific with one that is fundamentally based on charge conservation, which applies universally to all semiconductor devices regardless of material or structure.
3Measurement precision
If auxiliary winding voltage sensing is used for deadtime optimization, then deadtime control is achieved, but it requires additional hardware complexity
Solution Approach 1:
The patent extracts the deadtime control function from the auxiliary winding voltage sensing system and implements it using existing current sensing circuitry. Instead of requiring separate voltage sensing on auxiliary windings, the system uses the already-present current sensors to measure drain current during commutation. This extraction eliminates the need for additional auxiliary winding circuitry while maintaining deadtime control capability.
Solution Approach 2:
The patent makes the current sensing circuitry multi-functional by using it for both load current measurement and deadtime optimization. The same current sensors that measure load current are also used to integrate the current during voltage commutation to determine Coss charge. This multi-functionality eliminates the need for separate auxiliary winding voltage sensing circuitry, reducing overall system complexity while maintaining measurement precision.
4Measurement precision
If dedicated pins for nominal deadtime adjustment are used, then deadtime optimization is achieved, but it increases device complexity and pin count
Solution Approach 1:
The patent implements self-service deadtime optimization where the system automatically adjusts deadtime using feedback from current measurements during commutation. The controller autonomously determines the optimal deadtime by comparing measured current charge to reference Coss charge, eliminating the need for external adjustment pins or manual configuration. The system serves itself by using its own operational characteristics to determine and adjust its timing parameters.
Data Source
AI summary
Disclosed is a method for deadtime optimization in a half-bridge switch or full-bridge switch wherein high-side and low-side switches comprise GaN transistors; a circuit for implementing the method; and a power switching system comprising a GaN half-bridge or a GaN full-bridge and a deadtime optimization system. The circuit comprises a drain current bump filter for generating a current charge output; and circuit elements for comparing the current charge output to a reference current charge Coss and generating a deadtime adjust signal. The deadtime adjust signal may be used to adjust deadtime to reduce or minimize deadtime, and deadtime losses, while avoiding cross-conduction.