Switching Power Supply PWM Compensation for LPS Current Limiting
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Solution Overview
Problem
Existing switching power supplies face safety hazards due to excessive output current during short circuits or overloads, particularly in high power density applications like fast-charging chargers, and struggle to meet Limited Power Supply (LPS) requirements without compromising efficiency or reliability.
Innovation Solution
A switching power supply design incorporating a current-mode PWM control unit with a power compensation auxiliary circuit that adjusts the compensation voltage based on output voltage thresholds, ensuring safe operation by controlling the PWM duty cycle and maintaining output power within limits, while optimizing energy efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a PTC resistor is connected in series in the output loop to meet LPS requirements, then safety is improved, but power converter efficiency deteriorates and Level VI energy efficiency requirement cannot be met
Solution Approach 1:
The patent introduces a current detection circuit that detects the current in the primary winding and feeds back to the PWM control unit. This intermediary detection mechanism enables precise current control without adding series resistance to the output loop, thus maintaining efficiency while ensuring safety through active control rather than passive limitation.
Solution Approach 2:
The patent implements a feedback mechanism where the current detection terminal detects primary winding current and feeds back to the current-mode PWM control unit. This feedback loop enables real-time adjustment of the PWM duty cycle to maintain output current within safe limits, replacing the need for PTC resistors while preserving efficiency.
2Reliability
If a two-stage overcurrent protection circuit with current sampling resistor and comparator is used to meet LPS requirements, then safety is improved, but device complexity increases and cost increases
Solution Approach 1:
The patent integrates current detection and protection functions into the existing current-mode PWM control unit. The current detection terminal serves multiple purposes: it provides current information for PWM control and simultaneously enables overcurrent protection. This multi-functional approach eliminates the need for separate protection circuits, reducing complexity while maintaining safety.
Solution Approach 2:
The patent merges the overcurrent protection function with the existing current control circuitry. The current detection circuit and PWM control unit work together as an integrated system, combining protection and control functions into a single unified circuit rather than requiring separate two-stage protection circuits with additional components.
3Reliability
If power compensation is continuously provided to meet LPS requirements at low voltage, then safety is improved, but energy efficiency deteriorates
Solution Approach 1:
The patent implements dynamic power compensation where the compensation amount is adjusted based on real-time output voltage conditions. The PWM control unit dynamically modifies the duty cycle according to detected voltage levels, providing compensation only when necessary. This dynamic approach maintains safety during low-voltage conditions while avoiding unnecessary energy consumption during normal operation.
Solution Approach 2:
The patent changes the compensation parameter (PWM duty cycle) based on output voltage conditions. When output voltage drops below a threshold, the control unit increases compensation; when voltage is normal, compensation is reduced or eliminated. This parameter adjustment strategy ensures safety during fault conditions while maintaining energy efficiency during normal operation.
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
The solution effectively reduces the risk of excessive output current, meets LPS requirements, and enhances energy efficiency by dynamically adjusting power compensation, particularly beneficial for high power density applications like fast charging systems.
Implementation Method 1
a current-mode PWM control unit... comprising a current detection terminal Is used for detecting the current in a primary winding of the transformer
Implementation Method 2
transformer... a primary winding NP and a secondary winding NS
Implementation Method 3
the power compensation auxiliary circuit generates a DC voltage to provide a compensation voltage to the current detection terminal Is
Data Source
AI summary
A switching power supply, a power adapter and a charger are provided. The switching power supply comprises a current-mode PWM control unit, a transformer, and a DC power supply circuit connected in series to a power compensation auxiliary circuit. The current-mode PWM control unit comprises a current detection terminal. An input of the DC power supply circuit is connected to an auxiliary voltage output. The auxiliary voltage output outputs an auxiliary voltage related to output voltage of the switching power supply. The power compensation auxiliary circuit is used to compare the output voltage and a threshold voltage. When the current output voltage of the switching power supply is not greater than the threshold voltage, the power compensation auxiliary circuit generates a DC voltage, thus providing a compensation voltage to the current detection terminal, otherwise no compensation voltage is provided.