DC/DC Input Bypass Circuit for Reverse Connection Protection
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Solution Overview
Problem
Existing DC/DC conversion circuits suffer from significant losses when the input end is reversely connected to an external power supply, leading to potential damage of switch components due to excessive short-circuit currents and reduced switching speed, which decreases circuit efficiency.
Innovation Solution
A switch is placed between the input end and the power circuit, with a bypass circuit, including a diode, to create a unidirectional conduction path that isolates the power circuit when the input end is reversely connected, reducing losses and protecting the switch component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large-capacity Si 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 fast recovery diode for normal reverse connection protection and a controllable switch (MOSFET/IGBT) that can be activated only when actual reverse connection occurs. This segmentation allows the fast recovery diode to have small capacitance while the controllable switch provides the necessary current handling capability only when needed, thus reducing overall switching loss while maintaining protection reliability.
Solution Approach 2:
The protection circuit transitions from a static configuration (always-connected protection diode) to a dynamic configuration where the protection path is selectively activated. The controllable switch is turned on only when reverse connection is detected, allowing the circuit to optimize its characteristics: using the low-capacitance fast recovery diode during normal operation and engaging the high-current-capable switch only when protection is actually needed, thereby minimizing switching losses.
2Reliability
If a protection diode with high through-current capability is used to protect against reverse connection, then the reliability is improved, but the parasitic junction capacitance increases, reducing switching speed
Solution Approach 1:
The protection system is divided into two functional components: a fast recovery diode with low capacitance for rapid response to reverse voltage, and a controllable power switch with high current capability that is activated only when reverse connection is detected. This segmentation allows each component to be optimized for its specific function without compromising the other.
Solution Approach 2:
A control circuit acts as an intermediary between the detection of reverse connection and the activation of the high-current protection path. The control circuit detects reverse voltage conditions and selectively activates the controllable switch, mediating between the need for fast response (handled by the fast recovery diode) and the need for high current capability (provided by the controllable switch).
3Reliability
If the switching speed is reduced to protect the switch component, then the reliability is improved, but the switching loss increases and circuit efficiency decreases
Solution Approach 1:
The circuit dynamically adjusts its protection mechanism based on operating conditions. During normal operation, the fast recovery diode provides rapid protection with minimal impact on switching speed. When actual reverse connection occurs, the control circuit activates the controllable switch to handle the reverse current, providing robust protection only when necessary, thereby maintaining high circuit efficiency during normal operation while ensuring reliability during fault conditions.
Solution Approach 2:
The circuit changes its effective parameters (current handling capability, capacitance) based on operating conditions. The controllable switch alters the circuit's electrical characteristics dynamically: remaining off during normal operation to maintain fast switching performance, and turning on during reverse connection to provide high current capability and protection, thus optimizing both efficiency and reliability across different operating states.
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 by diverting reverse current through the diode and switch, preventing excessive short-circuit currents and maintaining switching speed, thereby enhancing the efficiency of the DC/DC conversion circuit.
Implementation Method 1
a bypass circuit, including a diode, to create a unidirectional conduction path that isolates the power circuit when the input end is reversely connected
Data Source
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AI summary
This application provides a DC/DC conversion circuit, including an input end, a power circuit, and an output end, and further including a bypass circuit. The bypass circuit is a unidirectional conduction circuit. A switch S is disposed between the input end and the power circuit, the input end is configured to be connected to one or more external power supplies, and the external power supply is configured to supply power to the DC/DC conversion circuit. The bypass circuit is connected between the input end and the power circuit, the bypass circuit is disposed between the switch S and the power circuit, and the bypass circuit is connected to the power circuit in parallel. The switch S is configured to be closed when the input end is reversely connected to the external power supply, so that a current output by a positive electrode of the external power supply flows back to a negative electrode of the external power supply through the bypass circuit and the switch S.