Indirect Input Voltage Detection via Switching Current Slope
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Solution Overview
Problem
Existing power converters require a resistor to sense input voltage, leading to power loss, especially at high input voltages, and increase the number of input terminals needed for protection, which is inefficient.
Innovation Solution
A method and circuit that utilize a current sense circuit to generate a current signal from a transformer's switching current, then use a detection circuit to determine the slope of this signal and generate an input-voltage signal without the need for a resistor, thereby reducing power loss and minimizing input terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistor is used to sense the input voltage for over-power protection, then the input voltage can be detected, but power loss increases especially when the input voltage is high
Solution Approach 1:
The patent extracts the voltage sensing function from the resistive voltage divider approach and implements it through the existing transformer and current sense circuitry. By sampling the current signal during specific periods when the power transistor is on, the circuit derives input voltage information without requiring a separate resistive sensing path, thereby eliminating the power loss associated with voltage sensing resistors
Solution Approach 2:
The patent makes the current sense circuit serve multiple functions: it provides both over-current protection information and input voltage sensing information. By processing the same current signal through different time periods and slope calculations, the circuit extracts multiple parameters (current magnitude and input voltage level) from a single signal source, eliminating the need for separate sensing components
2Reliability
If multiple input terminals are used for over-power protection, then comprehensive protection is achieved, but the device complexity increases
Solution Approach 1:
The patent enables the single current sense terminal to provide multiple protection functions by processing the current signal in different time periods. The same terminal provides both over-current protection (through continuous monitoring) and over-power protection (through slope analysis during specific periods), reducing the need for multiple dedicated input terminals while maintaining comprehensive protection
Solution Approach 2:
The patent merges the over-current protection function and over-power protection function into a single integrated processing path. By combining the current signal sampling, slope calculation, and voltage determination into one unified circuit architecture, the patent reduces the number of separate input terminals required while achieving both protection objectives
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
This approach effectively senses input voltage without resistors, reducing power loss and minimizing input terminals, enhancing efficiency and protection in power converters.
Implementation Method 1
A transformer (an inductive device) is used in the power converter for energy store and power transfer
Implementation Method 2
A resistor RS is connected serially with the power transistor 12 to generate a current signal VI in response to a switching current IP of the transformer 10
Data Source
AI summary
The present invention provides a method and circuit for detecting an input voltage of a power converter. It includes a current sense circuit for generating a current signal in response to a switching current of an inductive device. A detection circuit is coupled to sense the current signal for generating a slope signal in response to a slope of the current signal. A signal generation circuit is further developed to generate an input-voltage signal in accordance with the slope signal. The level of the input-voltage signal is corrected to the input voltage of the power converter.