DC-DC Converter Short Protection via Soft-Start Pin Control
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Solution Overview
Problem
Traditional DC-DC converters with PWM-based control mechanisms face issues when encountering a short-circuit at the output terminal, as they continue to generate abnormal high currents, leading to increased temperature and risk of damage without additional short-circuit protection.
Innovation Solution
A power supply apparatus incorporating a power conversion circuit, a control chip with soft-start function, and a short protection circuit that reduces the frequency and duty cycle of the PWM signal by pulling down the soft-start pin level when a short-circuit is detected, utilizing components like PNP-type BJTs, capacitors, and resistors to manage current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional PWM-based DC-DC converter operates without additional short-circuit protection, then the converter can maintain normal power conversion function, but the converter continuously generates abnormal large current when output terminal is short-circuited, leading to temperature increase and risk of damage
Solution Approach 1:
The patent implements preliminary protection action by using the soft-start circuit to proactively limit current during the startup phase and maintain reduced current during short-circuit conditions. The soft-start pin controls the PWM generator to produce limited-duty-cycle PWM signals, preventing abnormal large current generation before it can cause damage. This preliminary action transforms the soft-start mechanism from merely a startup feature into an active short-circuit protection mechanism.
Solution Approach 2:
The patent employs feedback mechanism where the short protection circuit continuously monitors the output status and provides feedback to the PWM generator through the soft-start pin. When short-circuit is detected, the feedback signal adjusts the PWM duty cycle to maintain safe current levels. This closed-loop feedback ensures the converter responds dynamically to short-circuit conditions and maintains reliability without generating harmful currents.
2Reliability
If short protection circuit is added to DC-DC converter, then the converter gains short-circuit protection capability, but the device complexity increases due to additional components
Solution Approach 1:
The patent achieves multi-functionality by making the soft-start circuit serve dual purposes: normal startup control and short-circuit protection. The same soft-start pin and associated components (resistors, capacitors) that control startup behavior also function as the short protection mechanism. This universality eliminates the need for separate dedicated short-protection components, reducing overall device complexity while maintaining reliability.
Solution Approach 2:
The patent merges the short protection function with the existing PWM control circuitry by integrating the protection mechanism into the PWM generator's control path. The short protection circuit combines multiple components (resistors, capacitors, transistors) into a unified control structure that works through the existing soft-start interface, rather than adding completely separate protection circuitry. This merging reduces complexity by utilizing existing structural elements.
Data Source
AI summary
A power supply apparatus is provided, and which includes a power conversion circuit, a control chip with soft-start function and a short protection circuit. The power conversion circuit is configured to provide a DC output voltage to a load in response to an output pulse-width-modulation (PWM) signal. The control chip is operated under a DC input voltage, and configured to generate the output PWM signal to control the operation of the power conversion circuit. The short protection circuit is configured to pull-down the level of a soft-start pin of the control chip, so as to substantially/significantly reduce the frequency and duty cycle of the output PWM signal, and then substantially/significantly reduce the current flowing through the shorted load.