DC-DC Converter Overcurrent Protection via Parallel Voltage Detection
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Solution Overview
Problem
Conventional DC-DC converters with overcurrent protection suffer from significant power loss and heat generation due to the detection resistor being in the main current path, leading to increased size and cost.
Innovation Solution
A DC-DC converter design that includes a voltage detection circuit with a detection resistor and a detection switching device, where the detection switching device is turned on after the output switching device is in the linear region, using a MOS transistor with higher ON resistance than the output switching device, to measure a mirror current and detect overcurrent without interfering with the main current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the detection resistor is placed in the main current path to detect overcurrent, then the overcurrent protection function is achieved, but the power loss and heat generation increase significantly
Solution Approach 1:
The current detection function is segmented from the main current path. A separate detection circuit with detection resistor Rd is created, which operates in parallel with the output switching device rather than in series with the main load current. This segmentation allows overcurrent detection without forcing the full load current through the detection resistor, thereby reducing power loss while maintaining protection functionality.
Solution Approach 2:
The detection switching device Qd acts as an intermediary that controls when the detection circuit is active. By turning on Qd only after the output switching device Qo is fully on, the circuit uses the voltage drop across Qo as the detection signal source without requiring the detection resistor to carry the full load current continuously. This intermediary approach enables indirect current measurement with minimal power loss.
2Reliability
If the detection resistor is placed in the main current path to detect overcurrent, then the overcurrent protection function is achieved, but the converter size and cost increase due to heat generation countermeasures
Solution Approach 1:
The detection function is separated into an independent parallel circuit branch. The detection resistor Rd and detection switching device Qd form a separate detection path that does not require large heat dissipation capabilities. This segmentation eliminates the need for large heat sinks or cooling structures that would be required if the detection resistor carried full load current, thereby reducing overall converter size.
Solution Approach 2:
The detection switching device Qd is turned on periodically or conditionally (after Qo is fully on) rather than continuously carrying full current. This periodic/conditional operation reduces the average power dissipation and heat generation in the detection circuit, eliminating the need for oversized thermal management components and reducing overall device 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 design reduces power loss and heat generation by minimizing the current through the detection resistor, preventing overcurrent detection errors and ensuring the output switching device's protection without increasing the converter's size or cost.
Implementation Method 1
detects a voltage corresponding to an electric potential difference between both ends of the output switching device
Implementation Method 2
an output switching device 1 made of a MOS transistor and smoothed into the DC output voltage Vout
Data Source
AI summary
In a DC-DC converter of this invention, a voltage detection circuit is connected in parallel with an output switching device, and the voltage detection circuit is put into operation a predetermined time after the output switching device is turned on. In addition, a detection switching device, which constitutes the voltage detection circuit, is designed to have a higher ON resistance than an ON resistance of the output switching device.