High-Side Driver Circuit With Bootstrap Start-Up for Depletion-Mode Switching
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Solution Overview
Problem
Conventional high-side driver circuits with bootstrap circuits are not suitable for depletion-mode transistors, as they fail to provide sufficient charging for the bootstrap capacitor, leading to reduced performance and the need for a floating or negative voltage source.
Innovation Solution
A high-side driver circuit design incorporating a power transistor, transistors, capacitors, diodes, and a start-up circuit that includes a third transistor and diode to manage charging and voltage levels, allowing the depletion-mode transistor to switch without reducing performance or requiring a floating voltage source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bootstrap circuit is used to drive the high-side power transistor, then the gate voltage can be floated with respect to the source voltage, but the charging is not enough for the bootstrap capacitor when driving depletion-mode transistors
Solution Approach 1:
The circuit performs preliminary charging of the bootstrap capacitor during the low-side switch conduction period. The low-side switch body diode conducts during this period, allowing current to flow through the bootstrap capacitor and charge it in advance before the high-side switch needs to turn on, ensuring sufficient voltage is available for proper switching.
Solution Approach 2:
The low-side switch body diode acts as an intermediary element that enables the charging of the bootstrap capacitor. By utilizing the inherent body diode of the low-side switch, the circuit creates a charging path for the bootstrap capacitor without requiring additional active components or complex control circuitry.
2Productivity
If the depletion-mode transistor is used as the high-side power transistor, then better performance is achieved, but the conventional bootstrap circuit cannot provide sufficient charging
Solution Approach 1:
The low-side switch body diode serves the dual purpose of its normal function and simultaneously charges the bootstrap capacitor for the high-side switch. This self-service mechanism eliminates the need for separate charging circuits and ensures the depletion-mode transistor can switch reliably by providing the necessary gate voltage through the bootstrap capacitor.
3Ease of operation
If a floating voltage source is used to obtain negative voltage for controlling depletion-mode transistor switching, then the required negative voltage can be obtained, but the circuit becomes more complicated
Solution Approach 1:
The low-side switch body diode serves as an intermediary that naturally generates the required voltage conditions for depletion-mode transistor control. During low-side conduction, the body diode forward voltage drop provides the necessary negative voltage relative to the high-side source, eliminating the need for separate floating voltage sources or negative voltage generation circuits.
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
Enables efficient switching of depletion-mode transistors without performance degradation and eliminates the need for a floating or negative voltage source, ensuring adequate charging of the bootstrap capacitor.
Implementation Method 1
a first capacitor (C1) having a first positive end and a first negative end, wherein the first negative end is coupled to the source of the first transistor
Implementation Method 2
a second capacitor (C2) having a second positive end and a second negative end, wherein the second positive end is coupled to the drain of the first transistor
Implementation Method 3
a first diode (D1) having a first anode and a first cathode, wherein the first anode is coupled to the first positive end of the first capacitor (C1)
Data Source
AI summary
The present invention provides a high-side driver circuit including a power transistor, the first transistor, the second transistor, the second capacitor, the second diode, a start-up circuit. The start-up circuit is coupled between a resistor and the second capacitor to complete a gate driving circuit. And, the aforementioned resistor can either be the gate resistance of the power transistor or an external resistor. The design of start-up circuit enables the functionality of the bootstrap capacitor of being charged to a designate voltage level. Thus, the depletion-mode transistor can be controlled to turn on/off without a floating voltage source or a negative voltage source.