DC/DC Converter Bypass Circuit for Reverse Polarity Protection
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Solution Overview
Problem
Existing DC/DC conversion circuits face significant losses and potential component damage when the input power supply is reversely connected due to excessive short-circuit currents, which is exacerbated by the use of high-capacity silicon diodes that increase junction capacitance and reduce switching speed.
Innovation Solution
Incorporating a bypass circuit with a switch and diode between the input end and the power circuit, allowing current to flow back through the bypass circuit when the input end is reversely connected, thereby isolating the power circuit and reducing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-capacity silicon diode is connected in parallel to protect the switching transistor from reverse connection, then the through-current capability is improved, but the parasitic junction capacitance increases, reducing switching speed and increasing switching loss
Solution Approach 1:
The protection function is segmented into two parts: a low-capacitance silicon diode for basic protection and a MOS tube for additional current handling capability. This segmentation allows each component to be optimized for its specific function, avoiding the need for a single high-capacitance diode that would degrade switching performance.
Solution Approach 2:
The MOS tube acts as an intermediary component between the silicon diode and the switching transistor. It provides an additional current path during reverse connection while having minimal impact on the switching transistor's junction capacitance, thus protecting the transistor without significantly increasing switching loss.
2Loss of energy
If a low-capacitance diode is used to minimize switching loss, then the switching speed is improved, but the through-current capability during reverse connection is insufficient, risking damage to the switching component
Solution Approach 1:
The protection scheme merges a low-capacitance silicon diode with a MOS tube in parallel. The diode provides fast switching performance with minimal capacitance, while the MOS tube supplements the current handling capability during reverse connection, ensuring both low switching loss and adequate protection.
Solution Approach 2:
The MOS tube serves multiple functions: it provides additional current path during reverse connection, shares the protection duty with the diode, and maintains compatibility with the existing switching circuit topology. This multi-functionality allows the system to achieve robust protection without sacrificing switching performance.
3Reliability
If the bypass circuit is added to handle reverse connection current, then the protection capability is improved, but the device complexity increases
Solution Approach 1:
The bypass circuit incorporates a controllable MOS tube that dynamically activates during reverse connection conditions. The controller detects reverse polarity and selectively turns on the MOS tube only when needed, rather than having it permanently in the circuit. This dynamic approach provides protection capability while minimizing the impact on normal circuit operation and reducing perceived complexity.
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 effectively reduces circuit losses and protects the switch component from overvoltage and overcurrent issues when the input end is reversely connected to the external power supply, enhancing the efficiency and reliability of the DC/DC conversion circuit.
Implementation Method 1
a diode is disposed between the switch and the power circuit... the bypass circuit is a unidirectional conduction circuit
Data Source
AI summary
A direct current (DC)/DC conversion circuit includes an input end, a power circuit, and an output end, a bypass circuit that is a unidirectional conduction circuit, and a switch disposed between the input end and the power circuit, where the input end is configured to be coupled to an external power supply to receive power to the DC/DC conversion circuit. The bypass circuit is coupled between the input end and the power circuit, the bypass circuit is disposed between the switch and the power circuit, and the bypass circuit is coupled to the power circuit in parallel. The switch is configured to be closed when the input end is reversely coupled to the external power supply to enable a current from a positive electrode of the external power supply to flow back to a negative electrode of the external power supply through the bypass circuit and the switch.