Dual-Capacitor Bootstrap Supply Circuit for High-Side Driver Stability
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Solution Overview
Problem
Existing half-bridge switching circuits face issues with insufficient driving voltage for high-side switching transistors due to insufficient charging of bootstrap capacitors, leading to improper operation.
Innovation Solution
A supply circuit for SMPS that includes dual capacitors and a charging-discharging control circuit to maintain stable supply for high-side drivers by charging and discharging the second capacitor based on switching signals, ensuring sufficient charge availability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bootstrap capacitor is used to provide driving voltage for the high-side switch, then the high-side switch can be driven, but the capacitor may not be charged sufficiently when the low-side switch has short turn-on time or is not turned on
Solution Approach 1:
The patent divides the single bootstrap capacitor into two separate capacitors: a first capacitor connected to the switching node for basic bootstrap function, and a second capacitor connected to the reference ground for supplemental charging. This segmentation allows each capacitor to perform its function independently, ensuring the first capacitor can be properly charged through the low-side switch while the second capacitor provides additional charge when needed.
Solution Approach 2:
The patent introduces a charging-discharging control circuit as an intermediary component that manages the charging and discharging of the second capacitor. This control circuit acts as a mediator between the power supply and the second capacitor, enabling precise control over when the second capacitor charges from the power supply and when it discharges to supplement the first capacitor, thereby ensuring sufficient driving voltage under all operating conditions.
2Reliability
If the low-side switch turn-on time is extended to charge the bootstrap capacitor, then sufficient driving voltage can be achieved, but the switching efficiency decreases
Solution Approach 1:
The patent implements preliminary action by having the second capacitor pre-charged from the power supply during periods when the low-side switch is on or during dead time. This preliminary charging ensures that when the first capacitor's charge becomes insufficient, the second capacitor is already ready to immediately supplement the charge without requiring extension of the low-side switch turn-on time, thus maintaining switching efficiency while ensuring adequate charging.
Solution Approach 2:
The patent changes the charging parameter by introducing a dual-capacitor architecture with independent charging paths. Instead of relying solely on the low-side switch turn-on time to charge the bootstrap capacitor (single parameter control), the system now uses two capacitors with different charging mechanisms: one charged through the switching node and another charged from the power supply through a dedicated control circuit, providing flexible parameter control to maintain both reliability and efficiency.
3Device complexity
If a single capacitor is used for bootstrap, then the circuit structure is simple, but the driving voltage becomes insufficient under certain operating conditions
Solution Approach 1:
The patent segments the single capacitor function into two separate capacitors with distinct roles and connection points. The first capacitor maintains the basic bootstrap function connected to the switching node, while the second capacitor provides supplemental charge connected to the reference ground. This segmentation resolves the contradiction by achieving driving voltage sufficiency through distributed capacitance while keeping each capacitor's function simple and well-defined.
Solution Approach 2:
The patent implements multi-functionality by designing the second capacitor to serve multiple purposes: it can be charged from the power supply during normal operation, discharge to supplement the first capacitor when needed, and work in conjunction with the charging-discharging control circuit to provide adaptive support under various operating conditions. This universal design ensures driving voltage sufficiency across different scenarios while adding minimal complexity to the overall system.
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
Ensures stable operation of high-side switching transistors by timely supplementing charges through the second capacitor, maintaining normal functioning even in conditions of long turn-on times.
Implementation Method 1
a first capacitor C1, a second capacitor C2... the first capacitor C1 includes a first terminal connected to the switching node SW, and a second terminal for providing a first supply voltage
Implementation Method 2
the second capacitor C2 includes a first terminal connected to a reference ground GND or a first potential terminal under control of the charging-discharging control circuit, and a second terminal for providing a second supply voltage
Implementation Method 3
the charging-discharging control circuit charges and discharges the second capacitor according to a charging-discharging enable signal
Data Source
AI summary
A supply circuit and a switched mode power supply (SMPS) are provided. The supply circuit includes a first capacitor, a second capacitor, and a charging-discharging control circuit; the first capacitor includes a first terminal connected to a switching node, and a second terminal for providing a first supply voltage; the second capacitor includes a first terminal connected to a reference ground or a first potential terminal under control of the charging-discharging control circuit, and a second terminal for providing a second supply voltage; and according to a charging-discharging enable signal, the charging-discharging control circuit charges the second capacitor in a first time period and discharges the second capacitor in a second time period.