Bootstrap Circuit With PMOS Charging for Startup-Stable Power Supplies
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Solution Overview
Problem
Existing bootstrap circuits in switching power supply apparatuses face inefficiencies due to the use of Schottky barrier diodes, which cause losses and potential startup failures when body diodes are used for charging boot capacitors, leading to reduced power efficiency and startup issues.
Innovation Solution
A circuit device incorporating a P-type MOS transistor and a Schottky barrier diode in the bootstrap circuit, where the boot capacitor is charged via the Schottky diode at startup and via the P-type MOS transistor during normal operation, ensuring the boot voltage meets the minimum operating requirements and reducing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Schottky barrier diode is used to charge the boot capacitor, then the forward voltage loss is reduced compared to a body diode, but power efficiency is still degraded due to continuous conduction losses
Solution Approach 1:
The bootstrap circuit dynamically switches between two charging paths: using the Schottky barrier diode during startup when the P-type MOS transistor is off, and using the P-type MOS transistor during normal operation when it is on. This dynamic operation allows the circuit to optimize between startup reliability (Schottky diode path) and power efficiency (MOS transistor path), resolving the contradiction between these two requirements.
2Loss of energy
If a P-type MOS transistor is used to charge the boot capacitor during normal operation, then power efficiency is improved by reducing conduction losses, but the circuit becomes more complex
Solution Approach 1:
The P-type MOS transistor is merged with the existing Schottky barrier diode in a parallel configuration, creating a unified bootstrap circuit that automatically selects the optimal charging path. This merging approach adds the MOS transistor functionality while maintaining compatibility with the existing Schottky diode structure, thereby improving power efficiency without proportionally increasing circuit complexity.
3Device complexity
If the boot capacitor is charged through the body diode of the MOS transistor at startup, then the circuit structure is simplified, but the boost voltage may fall below the minimum operating voltage of the driver
Solution Approach 1:
The Schottky barrier diode serves as an intermediary charging path during startup, providing a low-forward-voltage route to charge the boot capacitor before the P-type MOS transistor becomes active. This intermediary element ensures that the boot capacitor reaches sufficient voltage for driver operation without relying on the higher-forward-voltage body diode, thereby maintaining driver operation reliability while keeping the circuit structure relatively simple.
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 configuration enhances power efficiency by minimizing losses during normal operation while preventing startup failures, ensuring reliable operation of the switching power supply apparatus.
Implementation Method 1
a Schottky barrier diode having an anode coupled to the power supply node and a cathode coupled to the boot node
Implementation Method 2
a P-type MOS transistor provided between the power supply node and the boot node
Implementation Method 3
a boot capacitor is provided between the switch node and a boot node that supplies the boot voltage to the pre-driver
Data Source
AI summary
A circuit device includes a pre-driver that drives a gate of a first N-type MOS transistor provided between a power supply node and a switch node, and a bootstrap circuit that generates a boot voltage of the pre-driver from a power supply voltage. A boot capacitor is provided between the switch node and a boot node that supplies a boot voltage to the pre-driver. The bootstrap circuit includes a P-type MOS transistor provided between the power supply node and the boot node, and a Schottky barrier diode. The Schottky barrier diode has an anode coupled to the power supply node and a cathode coupled to the boot node.