Blocking Transistor Startup Control for Reverse-Conduction-Free Converters
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Solution Overview
Problem
Conventional voltage converter circuits face challenges in preventing reverse power conduction due to body diode leakage in high-side switching transistors, which can lead to uncontrolled voltage or current run-away, and require significant chip area for high voltage isolation tanks in charge pump circuits.
Innovation Solution
A voltage converter circuit design that includes a blocking transistor with a conduction path between a power terminal and a converter terminal, where the body diode conducts forward and blocks reverse current, and a driver circuit with a bootstrap terminal coupled to a bias input of a gate driver to efficiently control the blocking transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a blocking transistor is controlled to conduct in the forward direction, then reverse power conduction is prevented, but forward voltage drop increases and efficiency decreases
Solution Approach 1:
The patent changes the voltage parameter by using a charge pump circuit to generate a boosted voltage (higher than the input voltage) for driving the gate of the blocking NFET. This elevated gate voltage creates a stronger electric field that reduces the on-resistance and forward voltage drop of the blocking transistor, thereby improving efficiency while maintaining reliable reverse conduction blocking.
2Loss of energy
If a charge pump circuit with multiple high voltage isolation tanks is used to drive the blocking transistor, then forward voltage drop is reduced, but chip area consumption increases
Solution Approach 1:
The patent segments the charge pump circuit into multiple stages, where each stage generates a progressively higher voltage. The first stage generates an intermediate voltage, and the second stage boosts it to the final high voltage needed for the blocking transistor gate. This segmentation allows the use of lower voltage isolation tanks in each stage rather than requiring a single large high voltage isolation tank, thereby reducing overall chip area while achieving the necessary gate drive voltage.
3Productivity
If the blocking transistor is turned on during startup, then forward conduction is enabled, but reverse conduction may occur due to body diode leakage
Solution Approach 1:
The patent applies preliminary action by using the charge pump circuit to pre-charge the gate of the blocking NFET to a high voltage state before the converter begins operation. This ensures that when the blocking transistor is activated during startup, it is already in a strongly conductive state with minimal forward voltage drop, preventing the body diode from becoming forward-biased and causing reverse conduction. The preliminary voltage preparation eliminates the harmful reverse conduction effect during the critical startup phase.
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
The proposed solution effectively prevents reverse power conduction with minimal forward voltage drop and reduces chip area requirements by using a bootstrap capacitor to efficiently drive the gate of the blocking transistor, enhancing the efficiency and reliability of the voltage converter.
Implementation Method 1
A bootstrap capacitor is useful to quickly turn on a battery NFET coupled between the battery and a system power node, when supplementing system power from the battery. The quick turn on is provided to avoid crashing the system power node, while obtaining the reduced RDSON and thus small forward voltage drop of the NFET.
Implementation Method 2
A body diode of the blocking transistor: conducts current from the power terminal to the converter terminal; and blocks current from the converter terminal to the power terminal.
Data Source
AI summary
In a voltage converter, a blocking transistor has a conduction path between a power terminal and a converter terminal. A body diode of the blocking transistor: conducts current from the power terminal to the converter terminal; and blocks current from the converter terminal to the power terminal. A first switching transistor has a conduction path between the converter terminal and a switching terminal. A second switching transistor has a conduction path between the switching terminal and a ground terminal. A first gate driver has an output coupled to a control terminal of the first switching transistor. A second gate driver has an output coupled to a control terminal of the second switching transistor. A driver circuit has an output coupled to a control terminal of the blocking transistor. A bootstrap terminal of the driver circuit is coupled to a bias input of the first gate driver.