Bootstrap Capacitor Charging Circuit for High-Side Switch

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Solution Overview

Problem

Switching regulators with half-bridge circuits face challenges in minimizing power consumption and maximizing charge storage in bootstrap capacitors due to small capacitance, and existing solutions like using Schottky diodes are not easily integratable into single chips without external components.

Innovation Solution

A circuit arrangement and method for driving a high-side semiconductor switch using a signal-conditioning circuit, floating logic circuit, and floating driver, which generates set and reset signals based on input and phase-feedback signals to control the high-side switch, allowing for efficient charging of the bootstrap capacitor and minimizing power consumption by using short pulses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If the size of the bootstrap capacitor is kept small to minimize chip size, then the chip area is reduced, but the power consumption of the floating logic increases

Engineering Contradiction:

Improvechip areaVSAvoidpower consumption of floating logic

Core Design Contradiction:

Area of stationary objectVSUse of energy by moving object

Solution Approach 1:

The bootstrap capacitor is charged in advance during the low-side switch conduction period before the high-side switch needs to be activated. This preliminary charging action ensures that sufficient voltage is stored on the capacitor to drive the high-side gate, reducing the need for larger capacitance while maintaining reliable switching operation

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The bootstrap capacitor undergoes periodic charging and discharging cycles synchronized with the switching operation. During low-side conduction, the capacitor charges; during high-side switching, it discharges. This periodic operation allows the capacitor to maintain sufficient voltage with smaller capacitance value, thereby reducing chip area while managing power consumption through efficient charge utilization

Inventive Principle:

Principle #19Periodic action

2Quantity of substance

If a Schottky diode is used instead of a silicon diode to increase charge storage in the bootstrap capacitor, then the voltage drop is reduced and charge storage is improved, but the device complexity increases due to external components

Engineering Contradiction:

Improvecharge storage in bootstrap capacitorVSAvoiddevice complexity

Core Design Contradiction:

Quantity of substanceVSDevice complexity

Solution Approach 1:

The diode function is merged with the low-side switch by utilizing its body diode characteristic. The low-side switch is configured such that its intrinsic body diode provides the rectification function previously requiring a separate Schottky diode. This integration eliminates external components, reduces device complexity, and maintains efficient charge storage in the bootstrap capacitor

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The low-side switch serves multiple functions: it acts as the primary switching element for load control and simultaneously provides the rectification function through its body diode to charge the bootstrap capacitor. This multi-functionality eliminates the need for separate diode components while maintaining efficient charge storage

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Measurement precision

If low resistor values are used in the level-shifter to reduce signal degradation from noise, then the signal integrity is improved, but the load on the bootstrap capacitor increases

Engineering Contradiction:

Improvesignal integrityVSAvoidload on bootstrap capacitor

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The circuit incorporates feedback mechanisms where the actual gate voltage and current are monitored. This feedback information is used to dynamically adjust the level-shifter resistor values or switching timing, optimizing the balance between signal integrity and bootstrap capacitor loading. The feedback ensures that sufficient drive current is provided only when necessary, reducing overall power consumption while maintaining signal quality

Inventive Principle:

Principle #23Feedback

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 maximizes charge storage in the bootstrap capacitor and minimizes power consumption of the floating logic, enabling fail-safe operation without additional refresh circuits and allowing integration into a single chip without external components.

Implementation Method 1

a bootstrap capacitor with a first terminal connected to the second load terminal and with a second terminal connected to a second supply potential via a load path of a switching-device

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS7710167B2Circuits and methods for controlling an on/off state of a switch

Publication Date: 2010.05.04 INFINEON TECH AUSTRIA AG

AI summary

A circuit having a first circuit portion configured to receive a pulse-width modulated first signal and a second signal, and configured to generate third and fourth signals each responsive to the first and second signals; a second circuit portion configured to receive the third and fourth signals and to generate a fifth signal responsive to both the third and fourth signals; and a third circuit portion configured to control an on/off state of a first switch in response to the fifth signal, wherein the second signal is present at a load path terminal of the first switch. Also, various related methods.