Adaptive PWM Current Limiting for Constant-Power Supply Protection
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Solution Overview
Problem
Existing overcurrent protection mechanisms in DC power supplies fail to effectively protect circuits under varying power ratios, particularly when operating at high voltage and low current conditions, leading to potential damage due to exceeding the wattage limit of power elements.
Innovation Solution
A constant power adaptive current limiting protection circuit that includes a switching power supply circuit, detecting circuit, and controlling circuit, which dynamically adjusts the PWM signal based on output voltage and current to limit power to a protection threshold, ensuring operation within safe limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If preset overcurrent protection values are set to a constant value, then power elements are protected from damage under low voltage and high current conditions, but the protection fails under high voltage and low current conditions where the current cannot reach the protection setting value while power exceeds the wattage limit
Solution Approach 1:
The patent transforms the static constant current protection threshold into a dynamic adaptive threshold that automatically adjusts according to real-time output voltage and power conditions. The controlling circuit continuously monitors voltage and current, calculates instantaneous power, and dynamically updates the current threshold to match the maximum power rating of power elements, enabling effective protection across varying operating conditions including high voltage/low current scenarios
Solution Approach 2:
The patent changes the protection parameter from a fixed current value to a power-based adaptive threshold. By monitoring output voltage and calculating the corresponding safe current limit based on the power element's maximum power rating, the system adapts the protection threshold to different operating points, allowing it to detect overpower conditions regardless of whether the circuit operates at low voltage/high current or high voltage/low current
2Reliability
If the overcurrent protection mechanism is triggered, then the device shuts down to protect power elements, but this causes interruption of normal operation
Solution Approach 1:
Instead of completely shutting down the device when protection is needed, the patent applies partial action by dynamically adjusting the PWM duty cycle to limit output power to safe levels. The controlling circuit reduces the PWM signal magnitude just enough to keep power below the maximum rating, allowing the device to continue operating in a protected state rather than fully interrupting service
Solution Approach 2:
The patent implements a closed-loop feedback mechanism where the controlling circuit continuously monitors output voltage and current, compares instantaneous power against the maximum power rating, and adjusts the PWM signal in real-time. This feedback control enables the system to maintain safe operating conditions while preserving continuous operation, as the protection is achieved through dynamic adjustment rather than hard shutdown
Data Source
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AI summary
A constant power adaptive current limiting protection circuit includes a switching power supply circuit (102), a detecting circuit (104), and a controlling circuit (106). The switching power supply circuit (102) has at least one power switch assembly (108) and an output terminal (110). The detecting circuit (104) is coupled to the output terminal (110) of the switching power supply circuit (102) to detect an output voltage (VO) and an output current (IL1, IL2, IL3, IO) of the power signal (S2). The controlling circuit (106) is coupled to the switching power supply circuit (102) and the detecting circuit (104). The controlling circuit (106) is configured to output the PWM signal (S1), calculate a current limiting threshold based on a protection power and the output voltage (VO), and selectively execute a protecting action based on comparison between the output current (IL1, IL2, IL3, IO) and the current limiting threshold. The protecting action is adjusting the PWM signal (S1), so as to limit the output power of the switching power supply circuit (102) to below the protection power.