Half-bridge driver circuit with switched capacitor supply voltage
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Solution Overview
Problem
Existing half-bridge driver circuits for inverting buck-boost converters face challenges in effectively controlling the slew-rate of switching nodes to mitigate electromagnetic interference (EMI) across various operating conditions, particularly due to the inefficiencies of PMOS power transistors and the complexity of providing stable supply voltages for high-side and low-side FETs.
Innovation Solution
A half-bridge driver circuit architecture that uses n-channel FETs for both high-side and low-side switches, with a bootstrap capacitor powering the high-side driver circuit and a voltage regulator powering the low-side driver, ensuring stable supply voltages and enabling slew-rate control for both transistors across continuous conduction mode, discontinuous conduction mode, and pulse skip mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If PMOS power transistors are used for high-side switching, then the driver circuit can be simplified, but the performance and area occupancy are optimized poorly compared to n-channel FETs
Solution Approach 1:
The patent changes the transistor type parameter from PMOS to n-channel FET for the high-side switch, which requires a different driver circuit architecture but provides superior performance and smaller area occupancy. This parameter change is enabled by implementing a bootstrap circuit with switched capacitor supply voltage that generates the necessary positive supply voltage for the n-channel high-side driver.
2Reliability
If n-channel FETs are used for both high-side and low-side switches, then performance and area occupancy are optimized, but the complexity of providing stable supply voltages increases
Solution Approach 1:
The patent segments the power supply management into two independent parts: a bootstrap circuit for the high-side driver and a voltage regulator for the low-side driver. This segmentation allows each circuit to be optimized independently and simplifies the overall control logic, as the high-side driver automatically receives its supply voltage through the bootstrap mechanism during switching operations.
Solution Approach 2:
The bootstrap circuit implements self-service by automatically generating the positive supply voltage for the high-side driver using the switching action of the low-side FET and capacitor charging/discharging cycles. The circuit serves itself without requiring external control or additional active components, reducing the overall system complexity despite using n-channel FETs for both switches.
3Stability of the object's composition
If the high-side driver is powered by a bootstrap capacitor, then the supply voltage stability is improved across operating modes, but the circuit complexity increases
Solution Approach 1:
The patent implements a dynamic switched capacitor supply voltage system where the bootstrap capacitor is periodically charged and discharged based on the switching state of the low-side FET. This dynamic operation allows the high-side driver to receive a stable positive supply voltage relative to its source terminal, which floats with the switching node voltage, thereby maintaining stability across continuous conduction mode, discontinuous conduction mode, and pulse skip mode.
4Object-affected harmful factors
If slew-rate control is implemented for both high-side and low-side transistors, then EMI is reduced, but the driver circuit complexity increases
Solution Approach 1:
The patent implements a universal driver circuit architecture where both the high-side and low-side drivers use the same n-channel FET-based design with slew-rate control capability. This universal approach allows both drivers to function identically with respect to EMI mitigation, while the shared design methodology reduces overall complexity compared to using different transistor types or control mechanisms for each side.
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 solution optimizes the performance and area occupancy of the driver circuit, ensures correct slew-rate control for both high-side and low-side transistors, and maintains stable operation across all modes, effectively reducing EMI while simplifying the power supply management.
Implementation Method 1
a bootstrap capacitor powering the high-side driver circuit
Implementation Method 2
a voltage regulator powering the low-side driver
Data Source
AI summary
First and second FETs of a half-bridge are series connected between first and second terminals and are gate driven, respectively, by first and second drivers. An inductance is connected to the intermediate node of the half-bridge. Power supply for the second driver circuit is a supply voltage generated by a voltage regulator as a function of the voltage between the first and the second terminal. Power supply for the first driver circuit is a supply voltage generated by a bootstrap capacitor having a first terminal connected via a first switch to receive the supply voltage output from the voltage regulator and a second terminal connected to the intermediate node. The first terminal of the bootstrap capacitor is further connected by a second switch to receive a second supply voltage. A control circuit generates control signals for the first and second driver circuits and the first and second switches.