Algorithmic Current Sensing in PWM Power Supplies
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Solution Overview
Problem
Existing load current monitoring techniques in PWM SMPS devices often require additional resistors or parasitic resistances, leading to increased component costs, heat dissipation, and output voltage drops, while also facing accuracy issues due to noise and component lot variations.
Innovation Solution
An algorithmic approach that utilizes a PWM processor to monitor load current by adjusting pulse width based on input voltage and capacitance, eliminating the need for sense resistors and leveraging inherent PWM system characteristics to maintain constant output voltage and detect changes in load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense resistor is inserted between the inductor and load to monitor load current, then load current monitoring accuracy is improved, but component cost increases and heat dissipation increases
Solution Approach 1:
The patent extracts the current sensing function from the main power path by using a separate auxiliary winding on the transformer. This allows current monitoring without inserting a sense resistor into the high-current path, eliminating the heat dissipation problem while maintaining measurement capability through magnetic coupling.
Solution Approach 2:
The patent introduces an auxiliary winding as an intermediary element that magnetically couples the primary and secondary sides of the transformer. This intermediary provides a scaled-down version of the load current that can be measured without directly handling the full load current, reducing power loss while maintaining measurement accuracy.
2Measurement precision
If a sense resistor is inserted between the inductor and load to monitor load current, then load current monitoring accuracy is improved, but output voltage drop increases
Solution Approach 1:
The patent extracts the current sensing function from the main power path by using a separate auxiliary winding on the transformer. This allows current monitoring without inserting a sense resistor into the high-current path, eliminating the voltage drop issue while maintaining measurement capability through magnetic coupling.
3Ease of manufacture
If parasitic resistance of the switching element is used to monitor load current, then component cost is reduced, but measurement precision deteriorates due to component lot variations and environmental impact
Solution Approach 1:
The patent introduces an auxiliary winding as an intermediary that provides a stable, scaled representation of the load current. Unlike parasitic resistance which varies with temperature and manufacturing tolerances, the auxiliary winding provides a consistent magnetic coupling ratio that is much more stable over environmental conditions and component variations.
Solution Approach 2:
The patent uses the auxiliary winding to provide feedback information about the load current to the control circuit. This feedback mechanism allows the system to monitor and respond to load conditions accurately, compensating for any variations in the switching element characteristics through closed-loop control.
Data Source
AI summary
A power supply current monitor comprising a processor operable to monitor a pulsed voltage signal generated by a power supply and generate an alert when a pulse width for the pulsed voltage signal is outside an expected pulse width range; wherein the pulse width is dependent on an amount of current being supplied to a load by the power supply.