DC-DC Converter Bypass Capacitor Layout for Short-Circuit Protection
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Solution Overview
Problem
Existing in-vehicle DC-DC converters using ceramic capacitors for bypass protection face challenges of high cost, large size, and potential damage from short circuits due to high current flow, especially when multiple capacitors are required to achieve necessary capacitance and withstand voltage.
Innovation Solution
A DC-DC converter design incorporating a first and second bypass capacitor configuration, with a switch-controlled second bypass capacitor that turns off upon detection of a short circuit, reducing the number and capacitance of ceramic capacitors needed and preventing large current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple ceramic capacitors are connected in series to achieve necessary capacitance and withstand voltage, then the bypass capacitor can provide adequate protection, but the component cost and mounting area significantly increase
Solution Approach 1:
The bypass capacitor function is segmented into two parts: a first bypass capacitor connected to the voltage input terminal and a second bypass capacitor connected to the connection node between the first switch and third switch. This segmentation allows each capacitor to operate at lower voltage stress, enabling the use of smaller, lower-cost capacitors while maintaining overall protection capability.
Solution Approach 2:
The second bypass capacitor acts as an intermediary protection element between the first switch/third switch junction and the first bypass capacitor. This intermediary capacitor provides additional protection without requiring the first bypass capacitor to handle the full input voltage, thereby reducing the specifications and cost of the main bypass capacitor.
2Reliability
If multiple ceramic capacitors are connected in series to achieve necessary capacitance and withstand voltage, then the bypass capacitor can provide adequate protection, but the component cost increases
Solution Approach 1:
The bypass capacitor function is segmented into two parts: a first bypass capacitor connected to the voltage input terminal and a second bypass capacitor connected to the connection node between the first switch and third switch. This segmentation allows each capacitor to operate at lower voltage stress, enabling the use of smaller, lower-cost capacitors while maintaining overall protection capability.
Solution Approach 2:
The second bypass capacitor is designed as a relatively small, low-cost protective element that can be easily replaced if needed. By using a smaller, cheaper capacitor at the intermediate node rather than requiring a large high-voltage capacitor at the input terminal, the overall system cost is reduced while maintaining protection functionality.
3Object-affected harmful factors
If a bypass capacitor is short-circuited, then a large current may flow between the voltage input terminal and ground terminal, but installing two series of two capacitors increases the number of components to four
Solution Approach 1:
The protection function is segmented between two capacitors in different locations: the first bypass capacitor at the input terminal and the second bypass capacitor at the intermediate node. This segmentation provides redundant protection paths, ensuring that if one capacitor fails, the other can still limit overcurrent, while using only two capacitors total instead of four.
Solution Approach 2:
The second bypass capacitor serves as an intermediary protective element that provides overcurrent protection at the intermediate node. This intermediary capacitor works in conjunction with the first bypass capacitor to provide comprehensive protection with fewer total components, as each capacitor protects a specific portion of the circuit.
4Reliability
If surface-mount ceramic capacitors with higher withstand voltage and capacitance are used, then the bypass capacitor can handle surge conditions, but the cost and size increase
Solution Approach 1:
The voltage blocking function is segmented between the first bypass capacitor and the second bypass capacitor. The first capacitor handles the main bypass function at the input terminal, while the second capacitor at the intermediate node handles portion of the voltage stress. This segmentation allows both capacitors to be smaller with lower individual voltage ratings, reducing overall size while maintaining surge protection capability.
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
Reduces component cost and mounting area while preventing capacitor damage and improving IC stability by using fewer, smaller capacitors and reducing impedance, thus enhancing operational stability and noise reduction.
Implementation Method 1
a first bypass capacitor (C1, C2) and a second bypass capacitor (C3) are connected between the voltage input terminal (VIN) and the ground potential point (GND)
Implementation Method 2
an abnormality detection circuit that detects whether or not the second bypass capacitor (C3) is short-circuited
Implementation Method 3
the third switch (S3) opens when the abnormality detection circuit detects a short circuit in the second bypass capacitor (C3)
Data Source
AI summary
Disclosed is a DC-DC converter including: a first switch and second switch or rectifier in series between a voltage input terminal and a ground potential point; an inductor between the first switch and the second switch or rectifier; a control circuit controlling on/off of the first switch or the first and second switches according to feedback voltage of voltage output through the inductor, in which a third switch is connected between the voltage input terminal and the first switch, at least one first bypass capacitor is connected to the voltage input terminal, and a second bypass capacitor is connected to a second connection node between the first and third switches; and an abnormality detection circuit detecting short circuit of the second bypass capacitor by monitoring current in the first switch or voltage at the second connection node. The third switch turns off when short circuit is detected.