Power Supply On-Time Detection for Open-Loop and Short-Circuit Protection
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Solution Overview
Problem
Conventional power supplies face challenges in distinguishing between open-loop and short-circuit situations, leading to delayed protection and potential damage during short circuits.
Innovation Solution
Incorporating an on-time detection circuit to differentiate between open-loop and short-circuit conditions by detecting the on-time of the power switch, with a delay circuit that generates distinct turn-off signals for each scenario, allowing for immediate short-circuit protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional feedback detection is used to detect open-loop conditions, then open-loop protection can be provided, but the power supply cannot distinguish between open-loop and short-circuit situations, leading to delayed protection
Solution Approach 1:
The feedback detection function is segmented into two independent detection paths: one for open-loop detection (via feedback voltage) and another for short-circuit detection (via on-time detection). This segmentation allows each detection path to specialize in its specific function, enabling accurate distinction between open-loop and short-circuit conditions while providing immediate appropriate protection responses.
Solution Approach 2:
The on-time detection circuit acts as an intermediary that measures the duty cycle of the power switch and provides additional information to distinguish between open-loop and short-circuit conditions. By introducing this intermediate measurement mechanism, the system gains the capability to differentiate between the two fault types that would otherwise appear identical through conventional feedback detection alone.
2Device complexity
If a single delay circuit is used for both open-loop and short-circuit protection, then the circuit structure is simple, but the delay time cannot be adjusted for different protection scenarios
Solution Approach 1:
The delay circuit is made dynamic by allowing its delay time to be adjusted based on the detected fault condition. The delay time is extended for open-loop protection (to allow legitimate startup sequences) but kept short for short-circuit protection (for immediate safety response). This dynamic adaptation enables the same circuit structure to serve multiple protection scenarios with different timing requirements.
Solution Approach 2:
The delay time parameter of the delay circuit is changed based on the fault type detected. By modifying the delay time parameter dynamically - extending it for open-loop conditions and maintaining it short for short-circuit conditions - the system achieves adaptability for different protection scenarios without requiring fundamentally different circuit structures.
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
Enables rapid short-circuit protection and effective open-loop protection, preventing damage to the power supply and load-side circuits by accurately distinguishing between conditions and adjusting delay times accordingly.
Implementation Method 1
The transformer T1 has a primary winding NP and a secondary winding NS for storing energy and converting power. The transformer T1 is coupled to an input voltage VIN of the power supply for generating an output voltage VO. The power switch Q1 switches the transformer T1 for converting the energy stored in the primary winding NP to the secondary winding NS.
Implementation Method 2
A current sensing resistor RS is connected to the power switch Q1 in series. The current sensing resistor RS generates a current signal VCS in response to a primary-side switching current IP of the transformer T1.
Data Source
AI summary
The power supply according to the present invention comprises a transformer, a power switch, a signal generating circuit, an on-time detection circuit, and a delay circuit. The transformer receives an input voltage and generates an output voltage. The power switch switches the transformer for regulating the output voltage. The signal generating circuit generates a switching signal for controlling switching of the power switch. The on-time detection circuit detects an on-time of the power switch and generates a short-circuit signal. The delay circuit counts to a first delay time or to a second delay time in response to a feedback signal of the power supply and the short-circuit signal to generate a turn off signal for controlling the signal generating circuit to latch the switching signal.