MOSFET Gate Charge Recycling Circuit for High-Frequency DC-DC Converters
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Solution Overview
Problem
Inductive DC-DC converters face a fundamental trade-off between conduction and switching losses, particularly in miniaturized applications, due to the intrinsic on-resistance of power MOSFETs and the switching losses associated with gate capacitance, which are exacerbated by the need for high frequency operation and inductive ringing, leading to inefficiencies and voltage stresses.
Innovation Solution
A charge recycling circuit using a single inductor and switches for direct reciprocal recycling of gate charge between power MOSFETs, without affecting converter operation or control, by transferring gate capacitance charges from one MOSFET to another through an inductor during state transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If inductor size is reduced for miniaturization, then converter size decreases, but DCR conduction losses increase
Solution Approach 1:
The patent extracts the gate charge energy from the switching process and separates it from the main power conversion path. By removing this energy loss component through the recycling circuit, the system can use smaller inductors with higher DCR without proportionally increasing total losses, enabling miniaturization
2Speed
If switching frequency is increased for high frequency operation, then converter size decreases, but gate charging switching losses increase
Solution Approach 1:
The patent recovers gate charge energy at each switching cycle, and this recovery effect becomes more significant at higher frequencies. By capturing and recycling the gate charge that would otherwise be repeatedly charged and discharged at high frequency, the system reduces the cumulative switching losses that would normally increase linearly with frequency
Solution Approach 2:
The patent implements periodic charge transfer between MOSFETs synchronized with the switching frequency. This periodic charge recycling occurs at each switching cycle, and the cumulative effect over many cycles at high frequency results in significant reduction of total gate charging losses
3Speed
If rise/fall time is reduced for high frequency operation, then switching speed increases, but inductive ringing and voltage stresses increase
Solution Approach 1:
The patent performs preliminary charge transfer to the turning-on MOSFET before it actually switches on. By pre-charging the gate through the recycling inductor before the main switching event, the MOSFET turns on more smoothly with reduced ringing and voltage stresses, while still achieving high switching frequencies
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves higher power density and efficiency, with peak efficiencies up to 98.2% and 0.72 W/mm2 power density, especially at low load currents, by minimizing gate driver losses and ensuring non-overlap conditions.
Implementation Method 1
transferred to an inductor, stored in the inductor and then transferred directly to the gate of the other power MOSFET
Data Source
AI summary
A charge recycling circuit in an integrated circuit DC-DC converter having two power MOSFETs, the charge recycling circuit comprising a single inductor and recycling MOSFET switches arranged and sized such that when one of the two power MOSFETs is turning off, its gate capacitance charges are transferred to the single inductor, stored in the single inductor and then transferred directly to the gate of the other power MOSFET to turn it on.