H-Bridge Bootstrap Charging for Smaller Gate Drive Capacitors
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Solution Overview
Problem
Conventional bootstrap circuits in high-power applications, especially in hybrid H-bridge topologies, require large capacitors or additional components to manage charge distribution efficiently, leading to increased system size, weight, and reduced efficiency.
Innovation Solution
A modified bootstrap gate driver charging circuit that temporarily toggles the switching pattern of low-frequency switches using a short pulse during negative output voltage periods or when the capacitor voltage falls below a threshold, allowing the bootstrap capacitor to recharge without additional components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bootstrap circuit is used in hybrid H-bridge topologies with low-frequency switches, then the circuit can operate with standard components, but the bootstrap capacitor must be very large to hold sufficient charge during extended on-times
Solution Approach 1:
The patent applies periodic action by implementing a temporary toggling mechanism that periodically switches the switching pattern during the upper switch turn-on phase. This creates periodic charging opportunities for the bootstrap capacitor, allowing it to maintain sufficient charge without requiring a very large capacitance value. The toggling occurs for a short duration during the otherwise extended on-time period.
2Reliability
If the bootstrap capacitor is made larger to maintain charge during extended on-times, then continuous operation is reliable, but the system size and weight increase
Solution Approach 1:
The temporary toggling mechanism provides periodic recharging intervals, allowing the use of a smaller, lighter capacitor that can be rapidly recharged during these intervals rather than requiring a large capacitor that can sustain the entire extended on-time period alone.
3Volume of stationary object
If additional components such as buck converters or boost converters are added to recharge the bootstrap capacitor, then the capacitor can be smaller, but the system complexity and size increase
Solution Approach 1:
The patent implements self-service by using the existing switch network and power stage components to temporarily toggle and recharge the bootstrap capacitor, rather than adding separate external charging circuits like buck or boost converters. The system uses its own internal resources to maintain bootstrap capacitor charge.
Solution Approach 2:
The existing switch network is made multi-functional by temporarily deviating from the standard switching pattern to perform the additional function of recharging the bootstrap capacitor, rather than dedicating separate components solely for this purpose.
4Reliability
If the switching pattern is temporarily toggled to recharge the bootstrap capacitor, then the capacitor charge is maintained, but there may be concerns about oscillations and harmonic distortions
Solution Approach 1:
The patent applies partial action by implementing temporary toggling for only a short duration during the upper switch turn-on phase, rather than continuously altering the switching pattern. This limited-duration intervention is sufficient to recharge the bootstrap capacitor without causing significant oscillations or harmonic distortions that would result from prolonged or continuous toggling.
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 reduces the need for large capacitors, enhances system efficiency, minimizes size and weight, and avoids oscillations and harmonic distortions, improving overall inverter performance.
Implementation Method 1
the bootstrap circuit includes a bootstrap capacitor that is charged when the high-side switches are switched off and the low-side switches are on, and when the low-side switches are off, the bootstrap capacitor discharges to the gate driver that powers the high-side switches
Implementation Method 2
in response to the lower switch being turned ON and providing a path to ground with respect to the gate driver's supply voltage and in response to the lower switch being turned off, the charging circuit provides a sufficient voltage level to maintain the upper switch ON for the duration of the upper switch turn-on phase
Data Source
AI summary
A bootstrap gate driver charging circuit arranged to drive the gate of an upper switch (QU) and a lower switch (QL) connected in series to provide an AC output voltage (400) voltage by alternatively turning on and off according to a predetermined duty cycle of alternate upper switch turn-on and lower switch turn-on phases, the bootstrap gate driver charging circuit comprising: an input terminal; an output terminal; an H-bridge inverter with an inverter input and an inverter output; a charging path; and a bootstrap capacitor. The input inverter is electrically connected to the input terminal, the inverter output is electrically connected to a first end of the bootstrap capacitor, the charging path is electrically connected between a second end of the bootstrap capacitor and a gate driver supply voltage; wherein in response to the lower switch being turned ON and providing a path to ground with respect to the supply voltage.