PoE Output Current Sensing Using a Resistorless Current Mirror
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Solution Overview
Problem
Conventional Power over Ethernet (PoE) systems face challenges in accurately measuring the current drawn by powered devices due to the need for large transistors to handle voltage and current, leading to reduced accuracy in current measurement systems.
Innovation Solution
A resistorless current sensor approach is implemented in the Power Source Equipment (PSE) controller, using a sense transistor and current mirror to measure a replica current, allowing for more accurate current measurement without the need for large parallel resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a series resistor is used to measure current in conventional PoE systems, then current measurement can be achieved, but the transistor size must be large to handle voltage and current, which reduces measurement accuracy
Solution Approach 1:
The patent uses a current mirror circuit to create a replica (copy) of the main current flowing through the power transistor. Instead of measuring the large main current directly, the circuit measures a scaled-down copy current that is proportional to the main current. This allows accurate measurement without requiring the measurement components to handle the full current magnitude, thereby improving measurement accuracy while avoiding the need for large transistors in the measurement path.
2Use of energy by moving object
If a small parallel resistor value is chosen to conserve power, then power consumption is reduced, but the ability to accurately measure the series resistor is diminished
Solution Approach 1:
The patent measures the voltage across the series resistor by monitoring the copy current generated by the current mirror, rather than directly measuring the voltage drop across a small parallel resistor. The current mirror replicates the current flow characteristics, allowing the measurement system to infer the series resistor voltage drop from the copy current measurement. This approach enables accurate measurement without requiring a large parallel resistor that would consume excessive power.
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 solution enhances the accuracy of current measurement in PoE systems, improving the ability to detect valid powered devices and manage power distribution effectively while conserving power.
Implementation Method 1
A resistorless current sensor approach is implemented in the Power Source Equipment (PSE) controller, using a sense transistor and current mirror to measure a replica current
Data Source
AI summary
Power over Ethernet (PoE) communication systems provide power and data communications over the same communications link, where a power source device (PSE) provides DC power (for example, 48 volts DC) to a powered device (PD). The DC power is transmitted simultaneously over the same communications medium with the high speed data from one node to the other node. The PSE typically includes a controller that controls the DC power provided to the PD at the second node of the communications link. The PSE controller measures the voltage, current, and temperature of the outgoing and incoming DC supply lines to characterize the power requirements of the PD. The PSE controller includes a resistorless switch to measure the current. The resistorless switch includes a sense transistor and a current mirror to allowing the PSE controller to calculate the current based upon a replica current.