High Side Buck Converter Sensing Circuit for Voltage Ripple
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Solution Overview
Problem
High side buck converters face challenges in accurately sensing output voltage due to large voltage ripple and differing reference grounds, leading to poor load regulation and noise sensitivity, especially under varying load conditions.
Innovation Solution
A high side buck converter design incorporating a sensor and controller with an error amplifier and sensing window generator to accurately sense and regulate output voltage, using a sensing diode and capacitor to generate a sensing signal and an on-time signal for controlling switching transistors, while minimizing noise impact through controlled sensing windows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the switch node is designed as the reference ground of the control circuit to form a high side buck converter, then the control circuit can be protected from high voltage stress, but the output feedback signal cannot be directly sensed due to different reference grounds
Solution Approach 1:
The patent introduces an intermediary circuit consisting of a sensing capacitor and sensing diode that couples the output feedback signal to the switch node. This intermediary structure allows the feedback signal to be transferred across the different reference grounds (output ground and switch node ground) without direct connection, enabling the control circuit to sense the output voltage while maintaining the high side configuration's voltage protection benefits
Solution Approach 2:
The patent creates a copied version of the output feedback signal by charging the sensing capacitor through the sensing diode during the low side switch on-time. This copied voltage signal appears at the switch node and can be processed by the control circuit, effectively replicating the feedback information in a form that is compatible with the high side reference ground configuration
2Difficulty of detecting and measuring
If a sensing capacitor and diode are used to couple the feedback signal to the switch node, then output voltage sensing becomes possible, but noise sensitivity increases and load regulation deteriorates under varying load conditions
Solution Approach 1:
The patent employs periodic action by enabling the sensing capacitor to charge only during specific switching intervals (when the low side switch is on). This periodic charging mechanism, controlled by the switching rhythm, allows the feedback signal to be sampled at regular intervals, reducing noise accumulation and improving load regulation compared to continuous sensing approaches
Solution Approach 2:
The sensing capacitor is pre-charged during the low side switch on-time before the high side switch turns on. This preliminary charging action ensures that the feedback signal is captured and stored in advance, allowing the control circuit to process a clean, pre-conditioned signal rather than dealing with noisy real-time variations directly
3Measurement precision
If the sensing capacitor is continuously charged from the output feedback, then accurate voltage sensing is achieved, but the circuit becomes highly sensitive to noise and voltage ripple
Solution Approach 1:
The patent implements periodic charging of the sensing capacitor during specific switching intervals rather than continuous charging. This periodic operation, synchronized with the switching frequency, allows the capacitor to integrate feedback signal over defined periods while rejecting high-frequency noise and voltage ripple that occur outside the sensing windows
Solution Approach 2:
The sensing capacitor acts as a cushioning element that is charged beforehand during the low side switch on-time. This pre-charging process smooths out voltage variations and provides a stable voltage representation to the control circuit, cushioning against the harmful effects of noise and ripple that would otherwise directly affect the sensing accuracy
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 design improves load regulation by maintaining output voltage stability across varying loads, reducing the impact of noise and ensuring accurate voltage sensing, thereby enhancing the overall performance of high side buck converters.
Implementation Method 1
a sensor consisting of a sensing diode D2 and a sensing capacitor C2 is coupled between the system output VOUT and the switch node
Implementation Method 2
The anode of the sensing diode D2 is coupled to the system output VOUT
Data Source
AI summary
A high side buck converter includes a high side transistor, a low side transistor, a sensor, a sensing window generator, an error amplifier, a first comparator and an on-time signal generator. The high side and low side transistors are coupled together to form a switch node which is used as the reference ground of the controller. The sensor senses the output voltage and generates a sensing signal. The sensing window generator generates a sensing window signal. The error amplifier amplifies the error between a feedback signal of the sensing signal and a reference signal during the sensing window, and generates an error signal. The first comparator compares the feedback signal with the error signal and generates a first comparison signal. The on-time signal generator generates an on-time signal based on the first comparison signal, so as to control the high side and low side transistors.