Bootstrap Diode Emulator Circuit for Half-Bridge Driver
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Solution Overview
Problem
The existing bootstrap capacitor charging circuits fail to fully charge the capacitor when the voltage at the switched node is low, leading to insufficient voltage for the high side driver, due to the bootstrap diode emulator being off during such conditions.
Innovation Solution
A circuit that includes a phase sense comparator and a bootstrap diode emulator driver, which turns on the bootstrap diode emulator when the voltage at the switched node is low, ensuring continuous charging of the capacitor by comparing control voltages and enabling the emulator even when the low side input signal is low.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the bootstrap diode emulator is used to charge the bootstrap capacitor, then energy losses are reduced compared to a traditional diode, but the capacitor fails to charge fully when the voltage at the switched node is low
Solution Approach 1:
The patent employs a phase sense comparator that continuously monitors the voltage at the switched node and provides feedback control to the bootstrap diode emulator. When the switched node voltage is low, the comparator detects this condition and activates the emulator to charge the bootstrap capacitor, ensuring reliable operation while maintaining the low energy loss characteristics of the emulator topology
Solution Approach 2:
The patent implements dynamic control of the bootstrap diode emulator through a phase sense comparator that adapts the emulator's operation based on real-time voltage conditions. The emulator transitions from a static component to a dynamically controlled element that activates only when needed, optimizing both energy efficiency and charging reliability across varying operating conditions
2Use of energy by moving object
If the bootstrap diode emulator is turned off during normal operation, then energy efficiency is maintained, but the high side driver receives insufficient voltage when the switched node voltage is low
Solution Approach 1:
The phase sense comparator establishes a feedback mechanism that monitors the switched node voltage and triggers the bootstrap diode emulator only when the voltage drops below a threshold. This feedback-controlled activation ensures the high side driver receives adequate voltage during critical low-voltage periods while keeping the emulator inactive during normal operation to maintain energy efficiency
Solution Approach 2:
The patent implements preliminary detection of low-voltage conditions through the phase sense comparator, which identifies when the switched node voltage is low before the high side driver would fail. The emulator is activated in advance to charge the bootstrap capacitor, preventing voltage insufficiency before it occurs and ensuring continuous reliable operation
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 charging of the bootstrap capacitor by ensuring it remains charged even when the voltage at the switched node is low, thereby maintaining a stable high side floating supply voltage for the high side driver circuit.
Implementation Method 1
A circuit that includes a phase sense comparator and a bootstrap diode emulator driver, which turns on the bootstrap diode emulator when the voltage at the switched node is low, ensuring continuous charging of the capacitor by comparing control voltages
Implementation Method 2
The bootstrap diode emulator circuit 302 further employs a gate control circuit 410 for accepting a low side input signal LIN and driving the FET 405... The FET 405 is also connected to the bootstrap capacitor CBS and to the low side supply voltage DC2 VCC
Data Source
AI summary
A circuit for optimizing charging of a bootstrap capacitor connected to a high side floating supply voltage at a first terminal and to a switched node voltage at a second terminal, the circuit for optimizing being included in a gate driver circuit having high- and low-side driver circuits for driving high- and low-side switches connected at the switched node in a half bridge to provide current to a load, the high-side driver circuit receiving a first control voltage referenced to a first level and the low-side driver circuit receiving a second control voltage referenced to a second level, the bootstrap capacitor providing the high-side floating supply voltage for the high-side driver circuit, the optimizing circuit comprising a bootstrap diode emulator circuit comprising a bootstrap diode emulator driver circuit driving a first switch, the first switch connected between the first terminal of the bootstrap capacitor and a supply voltage for the low side driver circuit; and a phase sense comparator circuit responsive to the voltage at the switched node and turning ON the first switch when the voltage at the switched node is LOW, whereby charging of the bootstrap capacitor is optimized when the phase sense comparator circuit is enabled, the phase sense comparator circuit turning OFF or keeping OFF the first switch when the first control voltage goes to a level to turn ON the high-side switch or remains at such level or the bootstrap capacitor supply voltage goes high or remains high such that it is a fixed amount above the low-side driver supply voltage; further wherein the phase sense comparator circuit turns the first switch ON when: the second control voltage is at a level adapted to turn ON the low-side switch and the bootstrap capacitor supply voltage is low such that it is below the fixed amount above the low side driver supply voltage; or the first and second control voltages are both at a level such that the high-side and low-side switches are OFF after the second control voltage transitions from an ON state to an OFF state and the bootstrap capacitor supply voltage goes below the fixed amount above the low-side driver supply voltage; or the first and second control voltages are both at a level such that the high-side and low-side switches are OFF after the first control voltage transitions from an ON state to an OFF state and the bootstrap capacitor supply voltage goes below the fixed amount above the low-side driver supply voltage.