Power Converter Low-Side Switch Timing for Negative Current Limiting
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Solution Overview
Problem
Conventional power converters fail to effectively limit the on-time of the low-side switch, leading to excessive negative current flow that can damage the switch and other components when the load transitions from heavy or medium to light loads or when the input voltage increases abnormally.
Innovation Solution
Incorporating a low-side detecting circuit and control circuit to detect negative current or on-time signals, allowing the driver circuit to adjust the on-time of both high-side and low-side switches, thereby limiting the negative current within safe operational ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the driver circuit turns on the low-side switch when the load transits to light load or input voltage increases abnormally, then the power supplied to the load is reduced, but the negative current increases to excessive values causing damage to the low-side switch
Solution Approach 1:
The patent employs a feedback mechanism where the driver circuit monitors the on-time of the low-side switch and adjusts its operation accordingly. When the on-time exceeds a predetermined threshold during light load or abnormal voltage conditions, the driver circuit limits further conduction, thereby preventing excessive negative current while maintaining appropriate power reduction. This closed-loop control ensures both power management and switch protection.
Solution Approach 2:
The patent changes the operational parameters of the low-side switch by imposing a maximum on-time limit under specific conditions (light load or high input voltage). By dynamically adjusting the conduction time parameter rather than completely disabling the switch, the system achieves both power reduction and negative current limitation, resolving the contradiction between power supply and switch safety.
2Device complexity
If the driver circuit does not limit the on-time of the low-side switch, then the control is simple, but the negative current flows excessively damaging the low-side switch
Solution Approach 1:
The driver circuit incorporates a feedback mechanism that monitors the on-time of the low-side switch and compares it against a predetermined threshold. When the threshold is exceeded during light load or abnormal voltage conditions, the circuit automatically limits the on-time to prevent excessive negative current. This feedback-based approach adds minimal complexity while effectively protecting the switch.
Solution Approach 2:
The patent implements preliminary protective action by pre-setting a maximum on-time threshold for the low-side switch under specific operating conditions. Before excessive negative current can damage the switch, the driver circuit has already established the time limit, preventing the harmful condition from developing. This proactive approach maintains reliability without requiring complex real-time intervention.
Data Source
AI summary
A power converter of limiting a negative current is provided. The power converter includes a high-side switch, a low-side switch, a low-side detecting circuit, a control circuit and a driver circuit. The low-side detecting circuit detects a negative current flowing through the low-side switch or an on-time of the low-side switch to output a low-side detected signal. The control circuit outputs a control signal according to the low-side detected signal. The driver circuit, according to the control signal, outputs a high-side on-time signal to a control terminal of the high-side switch and outputs a low-side on-time signal to a control terminal of the low-side switch.