Bootstrap Charge Circuit for High-Side Driver Voltage Stability

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Solution Overview

Problem

Existing power supply circuits for high-side transistor switches in rectifier and inverter systems face challenges in maintaining a stable and accurately charged bootstrap capacitor, leading to variations in boosted supply voltage across process corners, temperature, and input rectified voltage, resulting in non-symmetrical on-resistance and potential overcharging that exceeds the safe operating area.

Innovation Solution

A circuit with a boot charge circuit that includes two current paths to selectively supply charging current to the bootstrap capacitor, one for switching mode and another for reset mode, using a combination of n-channel and p-channel transistors and diodes to manage charging and ensure proper electrostatic discharge protection, allowing for flexible transistor sizing and reduced ESD constraints.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single current path is used to charge the bootstrap capacitor, then the circuit complexity is reduced, but the power supply stability and voltage accuracy deteriorate across process corners, temperature, and input rectified voltage variations

Engineering Contradiction:

Improvecircuit complexityVSAvoidpower supply stability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The charging circuit is segmented into two distinct current paths: a first current path for switching mode operation and a second current path for reset mode operation. Each path is optimized for its specific operating condition, allowing the circuit to maintain stable and accurate bootstrap capacitor charging across different modes without requiring a single complex circuit that tries to handle all conditions equally well.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The circuit dynamically selects between two different charging paths based on the operating mode (switching mode or reset mode). This dynamic adaptation allows the circuit to optimize its charging behavior for each specific mode, improving power supply stability and voltage accuracy while keeping each individual path relatively simple.

Inventive Principle:

Principle #15Dynamics

2Use of energy by moving object

If the rectified voltage is reduced, then the energy consumption is reduced, but the bootstrap capacitor cannot be properly charged and operation fails

Engineering Contradiction:

Improveenergy consumptionVSAvoidcharging reliability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The circuit changes its charging parameters by switching between two different current paths depending on the rectified voltage level and operating mode. The second current path is specifically designed to enable proper bootstrap capacitor charging even when the rectified voltage is reduced, ensuring charging reliability across a wider voltage range while allowing energy-efficient operation at lower voltages.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If the high-side and low-side switches use different power supplies, then each switch can be optimized for its specific requirements, but the on-resistance becomes non-symmetrical and performance deteriorates

Engineering Contradiction:

Improveswitch optimizationVSAvoidon-resistance symmetry

Core Design Contradiction:

Adaptability or versatilityVSStability of the object's composition

Solution Approach 1:

The circuit ensures that both high-side and low-side switches experience the same gate-to-source voltage by using a common bootstrap capacitor charging mechanism. The two current paths are designed to charge the bootstrap capacitor to the same voltage level in both switching and reset modes, creating equipotential conditions that result in symmetrical on-resistance for both switches while still allowing mode-specific optimization.

Inventive Principle:

Principle #12Equipotentiality

4Productivity

If the bootstrap capacitor is over-charged to ensure sufficient drive voltage, then the high-side transistor can be fully enhanced, but the voltage exceeds the safe operating area and reliability deteriorates

Engineering Contradiction:

Improvetransistor drive capabilityVSAvoidsafe operating area compliance

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The circuit uses feedback control through the two current paths to precisely regulate the bootstrap capacitor charging voltage. The switching mode path and reset mode path are designed to charge the capacitor to the exact required voltage level without overcharging, ensuring that the high-side transistor receives sufficient drive voltage for full enhancement while maintaining voltage within the safe operating area through controlled charging mechanisms.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS11251691B2Floating power supply for a driver circuit configured to drive a high-side switching transistor

Publication Date: 2022.02.15 STMICROELECTRONICS ASIA PACIFIC PTE

AI summary

A high-side switching transistor of a rectifier circuit is driven by a high-side driver circuit to supply current to an output node. The high-side driver circuit is powered between a capacitive bootstrap node and the output node. A boot charge circuit charges the bootstrap capacitor by supplying current to the bootstrap node. The boot charge circuit includes: a first current path that selectively supplies a first charging current to the bootstrap node when the rectifier circuit is operating in a switching mode; and a second current path that selectively supplies a second charging current to the bootstrap node when the rectifier circuit is operating in a reset mode.