Primary-Side Controller With Valley-Based Current Limit Adjustment
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Solution Overview
Problem
Existing power converters with constant ON time (COT) control face issues with unregulated output voltage and increased conduction loss, particularly under heavy loads and low line voltage conditions, when operating in discontinuous-conduction mode (DCM) and boundary current mode (BCM).
Innovation Solution
A primary controller with a current peak upper limit adjustment circuit and gate control signal generation circuit adjusts the current peak upper limit based on the drain voltage of the synchronous switch, enabling operation in boundary current mode by increasing or reducing the current peak upper limit at specific valleys of the voltage waveform, thereby regulating the output voltage and reducing conduction loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the current peak upper limit is fixed to maintain fixed pulse frequency, then switching loss is reduced, but output voltage cannot be regulated when operating in boundary current mode
Solution Approach 1:
The patent employs dynamic current peak upper limit adjustment that responds to drain voltage conditions to enable output voltage regulation while maintaining efficient switching operation. The controller dynamically modifies the current peak upper limit based on feedback from the drain voltage, allowing the system to adapt between discontinuous-conduction mode and boundary current mode as needed for proper output voltage regulation, thereby resolving the contradiction between fixed-frequency efficiency and voltage regulation capability.
Solution Approach 2:
The patent implements a feedback mechanism that monitors the voltage at the drain of the synchronous switch and uses this information to adjust the current peak upper limit. This feedback loop enables the controller to detect operating mode (DCM or BCM) and appropriately adjust the current peak upper limit to maintain both efficient switching operation and proper output voltage regulation, resolving the contradiction between fixed-frequency operation and voltage regulation requirements.
2Ease of operation
If duty cycle is increased to regulate output voltage, then output voltage regulation is achieved, but conduction loss increases under heavy load conditions
Solution Approach 1:
The patent dynamically adjusts the current peak upper limit based on drain voltage conditions to optimize the balance between output voltage regulation and conduction loss. By increasing the current peak upper limit when heavy load conditions are detected (indicated by specific drain voltage levels), the system can achieve the required output voltage regulation with a more favorable duty cycle, thereby reducing conduction loss while maintaining voltage regulation capability under heavy load conditions.
Data Source
AI summary
A primary controller applied to a primary side of a power converter includes a current peak upper limit adjustment circuit and a gate control signal generation circuit. The current peak upper limit adjustment circuit increases a current peak upper limit of the primary side of the power converter when a gate control signal is enabled at a second valley of a voltage, and reduces the current peak upper limit when the gate control signal is enabled at an Nth valley of the voltage, wherein N is a positive integer. The gate control signal generation circuit is coupled to the current peak upper limit adjustment circuit, wherein the gate control signal generation circuit enables the gate control signal, disables the gate control signal according to the current peak upper limit, and the gate control signal is used for turning on a power switch of the primary side of the power converter.