Switching Mode Power Supply Virtual Current Sensing
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Solution Overview
Problem
Existing switching mode power supplies face challenges in accurately sensing output current due to delays in the feedback loop caused by sample-and-hold processes in middle current sensing techniques, which degrade transient performance and require additional pins for current sensing.
Innovation Solution
Implementing a real current sense circuit to monitor the current through the low-side power switch during its on-time and a virtual current sense circuit to monitor the high-side power switch, with a sense capacitor receiving both signals to generate a current sense signal that is used by the controller for control techniques like AVP and OCP, reducing the need for extra pins and minimizing delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If middle current sensing technique with sample-and-hold process is used, then current sensing is achieved, but large delay is generated in the feedback loop that degrades transient performance
Solution Approach 1:
The patent applies preliminary action by pre-charging the sense capacitor during the low-side switch on-time with a current proportional to the low-side switch current. This prepares the capacitor voltage in advance so that during the high-side switch on-time, the capacitor can immediately provide the correct sense voltage without waiting for sampling and holding operations, thereby eliminating feedback loop delay while maintaining accurate current sensing.
2Measurement precision
If inductor DCR current sensing method is used, then current sensing is achieved, but two additional pins are required on the controller
Solution Approach 1:
The patent applies universality by making the existing sense capacitor serve multiple functions: it continues to filter the current sense signal as before, and simultaneously stores the charged voltage that represents the current information during switching transitions. This eliminates the need for separate sampling capacitors and additional pins, as the sense capacitor becomes a multi-functional element that handles both filtering and current information storage.
3Measurement precision
If inductor DCR current sensing is used, then current sensing is achieved, but sensed current is affected by DCR at varied temperatures
Solution Approach 1:
The patent applies copying by creating a virtual copy of the inductor current through capacitive coupling rather than directly measuring the DCR current. The sense capacitor voltage is charged proportionally to the switch current and holds this information, providing a temperature-stable representation of the current that is independent of DCR variations with temperature.
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 enhances transient performance by directly sensing currents through both high-side and low-side power switches, reducing delays and eliminating the need for additional pins, thereby improving the accuracy and efficiency of current control in switching mode power supplies.
Implementation Method 1
a sense capacitor to receive the real current sense signal and the virtual current sense signal and to generate, based on the real current sense signal and the virtual current sense signal, a current sense signal
Data Source
AI summary
The present technology is related generally to a switching mode power supply with virtual current sensing. The switching mode power supply comprises a power stage that includes a first power switch and a second power switch coupled in series. The switching mode power supply senses a first current flowing through the first power switch during on-time and provides a virtual current sense signal that is proportional to a second current flowing through the second power switch during on-time. The switching mode power supply further combines the real current sense signal and the virtual current sense signal to form a current sense signal, which is sent to the controller to realize desired control.