Dynamic Current Limit Signal for PWM Power Supply Stability
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Solution Overview
Problem
In pulse width modulation (PWM) power supplies, constant current limit signals lead to unstable maximum output power due to signal propagation delays, causing increased power output as voltage increases.
Innovation Solution
A current control method and apparatus that updates the current limit signal based on detected maximum current values and ideal current limit values, using a limit signal generator to adjust the current limit signal periodically, ensuring it remains fixed during operation periods and is updated for subsequent periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a constant current limit signal is used, then the control circuit is simple, but the maximum output power becomes unstable due to signal propagation delay
Solution Approach 1:
The patent applies dynamics by transitioning from a static constant current limit signal to a dynamic time-varying current limit signal. The current limit signal now changes over time within each switching period, specifically increasing linearly or in steps, to compensate for the signal propagation delay. This dynamic adjustment ensures that the effective current limit remains stable despite the delay, resolving the contradiction between circuit simplicity and power stability.
Solution Approach 2:
The patent changes the parameter of the current limit signal from a constant value to a time-varying value. By modifying the signal's temporal characteristic (from DC to ramp or stepped waveform), the system compensates for the fixed propagation delay. The signal's amplitude or level changes over time to account for the delay, maintaining stable maximum output power while keeping the control circuit relatively simple.
2Stability of the object's composition
If the current limit signal is updated frequently, then the maximum output power stability improves, but the control complexity increases
Solution Approach 1:
The patent implements periodic action by updating the current limit signal at regular intervals synchronized with the switching period of the power supply. Rather than continuous complex processing, the signal is updated periodically - either once per switching cycle or at specific phases within each cycle. This periodic update strategy achieves stable maximum output power while avoiding excessive control complexity by leveraging the natural periodicity of the switching operation.
Data Source
AI summary
Current control method and apparatus are disclosed. A current limiter is coupled to a switch connected in series with an energy transfer element of a power supply. The current limiter detects a current flowing through the switch and, when the current exceeds a current limit signal, turns off the switch. A limit signal generator provides the current limit signal, detects the maximum current value of the current, and updates the current limit signal according to the maximum current value and an ideal current limit value.