DC-DC Converter Current Limiting via Intermediate Voltage Control
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Solution Overview
Problem
Digitally controlled DC to DC converters face challenges in implementing a simple and cost-effective steady state current limitation mechanism to protect the converter and load from over-currents.
Innovation Solution
A method that involves storing values representative of output voltage levels when current thresholds are exceeded or fallen below, modifying the control signal to bring the output voltage to an intermediate level between these values, and maintaining this signal for a fixed time delay before adjusting it further based on new voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a steady state current limitation mechanism is implemented in a digitally controlled DC to DC converter, then the converter and load are protected from over-currents, but the device complexity and cost increase
Solution Approach 1:
The patent uses a digital copy of the voltage error signal instead of an analog current signal. The controller stores a copy of the voltage error signal at the moment current threshold is exceeded, and uses this digital copy to generate the control signal. This eliminates the need for separate analog current sensing circuitry while maintaining protection functionality.
Solution Approach 2:
The patent replaces analog current sensing and limiting circuitry with digital signal processing. The current limitation function is achieved through digital storage and manipulation of voltage error signal samples, substituting complex analog mechanisms with simpler digital operations in the controller.
2Reliability
If traditional analog current sensing and limiting circuitry is used, then current protection is achieved, but the device complexity and cost increase
Solution Approach 1:
The patent makes the controller perform multiple functions: it simultaneously controls the output voltage and implements current limitation using the same digital processing resources. The controller uses the voltage error signal, which is already being processed for voltage control, and repurposes it for current limitation by storing and manipulating digital samples of this signal.
Solution Approach 2:
The patent creates a digital copy of the voltage error signal at the moment current threshold is exceeded. This digital copy is then used to generate the control signal for current limitation, eliminating the need for separate analog current sensing circuitry and reducing manufacturing complexity.
3Reliability
If the control signal is continuously adjusted to maintain precise current limitation, then current protection is improved, but output voltage oscillations increase
Solution Approach 1:
The patent stores the voltage error signal at the moment current threshold is exceeded, capturing the state before oscillations can develop. The control signal is then generated based on this pre-captured value, preventing continuous adjustment that would cause oscillations while maintaining effective current limitation.
Solution Approach 2:
The patent uses periodic sampling of the voltage error signal at critical moments (when current thresholds are exceeded) rather than continuous adjustment. This periodic action based on threshold events provides current limitation while avoiding the oscillations that would result from continuous control signal adjustment.
Data Source
AI summary
In an embodiment a current limiting circuit includes a circuit configured to detect when an input or output current of a DC to DC converter exceeds or falls below a threshold and a controller configured to store a first value representative of a level of an output voltage of the DC to DC converter in response to the input or output current exceeding or falling below a first threshold, store a second value representative of the level of the output voltage in response to the input or output current falling below a further threshold and modify a control signal based on the first and second values, wherein the control signal is modified based on the first and second values so that the control signal brings the output voltage to an intermediate voltage level between the level of the output voltage represented by the first value and the level of the output voltage represented by the second value.