Bootstrap Charge Storage Recharge via Back-EMF
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Solution Overview
Problem
In driver circuits using N-channel MOSFET devices, the bootstrap capacitor discharges during the off state, requiring recharging during the on state, leading to initial current limitation and heat generation due to insufficient bias voltage, which is undesirable and unacceptable in power-saving requirements.
Innovation Solution
A charging circuit that utilizes back electromotive force (BEMF) voltage spikes from an inertial load, such as a DC motor, to recharge the bootstrap capacitance without drawing power from the supply, by employing a detection component and current source to capture voltage spikes and store energy in the capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a charge pump is used to recharge the bootstrap capacitor during the off state, then the bootstrap capacitance is maintained, but power consumption occurs during the off state which violates power-saving requirements
Solution Approach 1:
The bootstrap capacitor recharges itself during the on state by utilizing the voltage spike generated when the NMOS device turns on. The capacitor captures energy from the inherent voltage transient during switching, eliminating the need for external power consumption during the off state while maintaining its charge level.
Solution Approach 2:
The bootstrap capacitor is recharged in advance during the on state before the off state begins. This preliminary charging action ensures that sufficient voltage is available at the start of the off state without requiring power consumption during the off state itself, thus meeting power-saving requirements.
2Use of energy by moving object
If the bootstrap capacitor is allowed to discharge during the off state, then power saving is achieved, but initial current limitation and heat generation occur during the on state due to insufficient bias voltage
Solution Approach 1:
The bootstrap capacitor is recharged in advance during the on state before the off state begins. This preliminary charging ensures that sufficient bias voltage is available at the start of the off state, preventing current limitation and heat generation during the subsequent on state while achieving power saving during the off state.
Solution Approach 2:
The bootstrap capacitor maintains its charge continuously by recharging during each on state and discharging during each off state, ensuring uninterrupted bias voltage supply. This continuous cycle eliminates periods of insufficient voltage that would cause current limitation and heat generation, while still achieving net power saving during off states.
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
Prevents bootstrap capacitance discharge during the off state, eliminating the need for initial recharging and maintaining high bias voltage for NMOS device saturation, thus reducing current limitation and heat generation, while adhering to power-saving constraints.
Implementation Method 1
A detection component is provided and arranged to detect if an output voltage of the switching element is less than a negative threshold voltage level
Implementation Method 2
A charging circuit that utilizes back electromotive force (BEMF) voltage spikes from an inertial load, such as a DC motor, to recharge the bootstrap capacitance
Implementation Method 3
A bootstrap charge storage device is provided within an inertial load driver circuit. A charging circuit is provided and arranged to recharge the bootstrap charge storage device
Data Source
AI summary
A charging circuit for at least one bootstrap charge storage element within an inertial load driver circuit is described, the at least one bootstrap charge storage element comprising a first node operably coupled to an output node of at least one switching element of the inertial load driver circuit. The charging circuit comprises at least one current source controllable to provide a current to a second node of the at least one bootstrap charge storage element, and at least one detection component arranged to receive at a first input thereof an indication of a voltage level at the output node of the at least one switching element of the inertial load driver circuit, detect when the voltage level at the output node of the switching element of the inertial load driver circuit is below a negative threshold voltage level, and control the at least one current source to provide a current to the second node of the at least one bootstrap charge storage element when the voltage level at the output node of the switching element of the inertial load driver circuit is below the negative threshold voltage level.