Primary-Side Converter Control for 125 Ns Voltage Sampling
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Solution Overview
Problem
Switching power converters face challenges in sensing output voltage during light load conditions due to short discharge modes, making it difficult for related-art controllers to accurately sample the voltage on the auxiliary winding.
Innovation Solution
A primary-side controller employs a three-step process using three capacitors to sample and hold the output voltage, where one capacitor is reset and pre-charged in one switching period, another samples the voltage in the next period, and the third capacitor is prepared for the subsequent period, enabling accurate voltage regulation even in short discharge modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional controller samples output voltage during discharge mode, then voltage regulation can be achieved, but in light load conditions the discharge mode becomes too short for accurate sampling
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor during the charge mode before the discharge mode begins. This allows the capacitor to be ready to capture the voltage sample immediately when the discharge mode starts, enabling accurate sampling even when the discharge mode duration is very short (125 ns or less). The capacitor is prepared in advance (pre-charged to a known voltage level) so that it can quickly track and hold the voltage without requiring a long sampling window.
2Measurement precision
If the discharge mode is extended to allow accurate voltage sampling, then sampling accuracy improves, but power loss increases due to extended non-conductive period
Solution Approach 1:
The patent eliminates the need to extend the discharge mode by performing preliminary action - pre-charging the capacitor during the charge mode. This allows the controller to accurately capture the voltage sample at the very beginning of the discharge mode and then quickly terminate the discharge mode, minimizing energy loss while maintaining sampling accuracy.
Solution Approach 2:
The capacitor serves itself by being pre-charged during the charge mode to the appropriate voltage level, eliminating the need for external intervention or extended discharge time to prepare for sampling. The capacitor automatically tracks and holds the voltage during the brief discharge mode, enabling accurate measurement without extending the non-conductive period.
3Measurement precision
If a dummy load is added to extend discharge mode for sampling, then sampling becomes possible, but device complexity and component count increase
Solution Approach 1:
The patent makes the existing capacitor multi-functional by having it serve both as the output filter capacitor and as the sampling/holding capacitor. The same capacitor that maintains the output voltage also captures and holds the voltage sample during the discharge mode, eliminating the need for separate sampling components or dummy load circuits.
Solution Approach 2:
The existing capacitor in the circuit serves itself by being pre-charged during the charge mode and then automatically capturing the voltage sample during the discharge mode. This self-service capability eliminates the need for additional components or circuits to enable voltage sampling, maintaining simplicity while achieving the sampling function.
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 allows the controller to accurately sample and regulate output voltage in discharge modes as short as 125 ns, improving efficiency and eliminating the need for a dummy load, even in low load situations.
Implementation Method 1
a first capacitor holding a sample from a previous switching period
Implementation Method 2
sampling a voltage on the auxiliary winding with a second capacitor
Implementation Method 3
resetting and pre-charging a third capacitor
Data Source
AI summary
Switching power converters, and methods and primary-side controllers for controlling same. One example is a method of controlling a switching power converter, the method comprising: asserting drive signals applied to a primary switch during a plurality of switching periods; during a first switching period, controlling assertion of a first drive signal based on a sample held by a first capacitor, sampling instantaneous output voltage with a second capacitor, and pre-charging a third capacitor; during a second switching period, controlling assertion of a second drive signal based on a sample held by the second capacitor, sampling instantaneous output voltage with the third capacitor, and pre-charging the first capacitor; and during a third switching period, controlling assertion of a third drive signal based on a sample held by the third capacitor, sampling instantaneous output voltage with the first capacitor, and pre-charging the second capacitor.