Bootstrap Diode Circuit Using High-Voltage PMOS Transistor
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Solution Overview
Problem
Conventional bootstrap circuits in half-bridge gate driver circuits face issues with external Schottky diodes requiring extra components and PCB space, internal diodes experiencing high reverse leakage or forward voltage drops, and complex designs involving multiple components.
Innovation Solution
A single high-voltage p-type metal-oxide-semiconductor field effect transistor (PMOSFET) switch is used as the bootstrap diode circuit, with a bootstrap control circuit providing a constant gate-source voltage to turn on the PMOSFET independently of power supply voltage, minimizing forward voltage drop and reverse leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an external Schottky diode is used in the bootstrap circuit, then the reverse leakage current is reduced, but the component count and PCB area increase
Solution Approach 1:
The patent combines the diode function with an internal PMOS transistor to replace the external Schottky diode. The PMOS transistor's body diode provides the required rectification function while the transistor itself can be controlled to achieve low reverse leakage current, eliminating the need for separate external diode components.
Solution Approach 2:
The patent introduces a control circuit as an intermediary to manage the PMOS transistor's operation. This control circuit enables the PMOS to function as a smart diode with controllable reverse leakage characteristics, mediating between the bootstrap capacitor and the rest of the circuit while maintaining low leakage performance.
2Device complexity
If an internal Schottky diode is used in the bootstrap circuit, then the component count is reduced, but the reverse leakage current increases at high reverse voltages
Solution Approach 1:
The patent changes the key parameter of the switching device from Schottky diode to PMOS transistor. This parameter change enables controlled operation where the PMOS can be turned off or operated in specific regions to minimize reverse leakage current at high voltages, while maintaining the integrated circuit advantage of reduced component count.
Solution Approach 2:
The control circuit acts as an intermediary that manages the PMOS transistor's operation to achieve low reverse leakage. By controlling the gate voltage of the PMOS, the control circuit mediates the trade-off between maintaining conduction and minimizing leakage at high reverse voltages.
3Device complexity
If an internal p-n junction diode is used in the bootstrap circuit, then the component count is reduced, but the forward voltage drop increases
Solution Approach 1:
The patent changes the device type from p-n junction diode to PMOS transistor. This parameter change allows for a much lower on-resistance in the PMOS channel compared to the forward voltage drop of a p-n junction diode, significantly reducing the voltage drop and power loss in the bootstrap circuit while maintaining integration benefits.
4Loss of energy
If a combination of PMOS transistor and JFET is used in the bootstrap circuit, then the forward voltage drop is reduced, but the device complexity and design difficulty increase
Solution Approach 1:
The patent extracts and removes the JFET component from the circuit, retaining only the PMOS transistor. The PMOS transistor alone is sufficient to achieve low forward voltage drop through its low on-resistance characteristic, eliminating the need for the complex PMOS-JFET combination and associated design challenges.
5Reliability
If a high-voltage NMOS transistor is used in the bootstrap circuit, then the device can handle high voltage, but a charge pump is needed increasing component count
Solution Approach 1:
The patent inverts the device type selection from NMOS to PMOS transistor. The PMOS transistor's natural characteristics, including its body diode orientation and threshold voltage behavior, allow it to function effectively in the bootstrap circuit without requiring an external charge pump, thereby achieving high voltage handling with fewer components.
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 reduces component count, minimizes forward voltage drop, and eliminates forward injection current, offering a simpler and more efficient bootstrap diode circuit with near-to-zero voltage drop and low reverse leakage.
Implementation Method 1
The high-voltage PMOS transistor has a breakdown voltage higher in magnitude than a voltage drop between a maximum bootstrap voltage and a power supply voltage
Implementation Method 2
A constant current source can be used to provide a constant gate-source voltage for turning on the PMOSFET switch independent of the power supply voltage
Data Source
AI summary
A bootstrap diode circuit includes an anode for coupling to a power supply voltage terminal and a cathode for coupling to a bootstrap voltage terminal. The bootstrap diode circuit also includes a high-voltage p-type metal-oxide-semiconductor (PMOS) transistor, having a source forming the cathode of the bootstrap diode circuit and a drain forming the anode of the bootstrap diode circuit. The high-voltage PMOS transistor has a breakdown voltage higher in magnitude than a voltage drop between a maximum bootstrap voltage and the power supply voltage.