Switching Power Supply Controller Precharge Circuit for Bootstrap Voltage
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Solution Overview
Problem
Current resonance switching power supplies face issues with maintaining the voltage of the high-side power source during burst operations in standby mode, leading to potential off-resonance phenomena and damage when the load state changes from no-load to light-load or normal-load, due to continuous energy consumption by the high-side drive circuit and lack of bootstrap capacitor charging.
Innovation Solution
A switching power supply controller with a precharge circuit that detects a switching stop period and outputs a precharge signal to charge the bootstrap capacitor for a short period when the voltage falls below a threshold, ensuring the high-side power source voltage is maintained during extended switching stop periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the switching element is stopped for a long period during burst operation to reduce standby power consumption, then standby power consumption is reduced, but the high-side power source voltage may fall below the threshold needed to maintain high-side drive circuit operation
Solution Approach 1:
The precharge circuit performs preliminary charging of the bootstrap capacitor before the switching element is stopped during burst operation. By detecting the stop period duration and activating the precharge circuit in advance, the high-side power source voltage is maintained at a level sufficient for reliable drive circuit operation when switching resumes, preventing off-resonance phenomena.
Solution Approach 2:
The control circuit monitors the stop period duration of the switching element and provides feedback to determine when to activate the precharge circuit. This feedback mechanism ensures the precharge operation is triggered at the appropriate time to maintain voltage levels without continuously operating the synchronous rectifier switch, thus reducing standby power consumption while ensuring reliability.
2Reliability
If the synchronous rectifier switch is continuously operated to maintain high-side power source voltage, then the voltage is maintained reliably, but standby power consumption increases
Solution Approach 1:
Instead of continuous operation, the synchronous rectifier switch is operated periodically only when needed. The precharge circuit is activated intermittently based on the detected stop period duration, performing voltage maintenance only during critical intervals when the switching element is stopped for extended periods, thereby reducing overall standby power consumption while maintaining voltage stability when required.
3Loss of energy
If the bootstrap capacitor is not charged during switching stop period, then standby power consumption is reduced, but the voltage of the high-side power source falls below the threshold voltage
Solution Approach 1:
The precharge circuit performs preliminary charging of the bootstrap capacitor during extended stop periods before the switching element is restarted. This preliminary action ensures that when the load state changes from no-load to light-load or normal-load, the high-side power source voltage is already at a sufficient level, preventing off-resonance phenomena and ensuring reliable operation without continuous charging.
Solution Approach 2:
The system uses its own switching element to provide the charging function for the bootstrap capacitor during stop periods. By controlling the switching element to perform a brief conduction period that charges the bootstrap capacitor, the system serves itself without requiring external charging circuits or continuous operation of additional components, thus maintaining reliability while minimizing energy consumption.
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 solution effectively prevents off-resonance by maintaining the high-side power source voltage during burst operations, reducing standby power consumption while ensuring reliable operation when the load state changes, without continuously operating the synchronous rectifier switch.
Implementation Method 1
an oscillation circuit which generates an on-trigger signal and an off-trigger signal at a switching frequency corresponding to a voltage signal
Implementation Method 2
a precharge circuit which receives from the control circuit a burst operation signal, indicative of a burst operation in a standby mode, and which supplies for a second period a precharge signal that causes the control circuit to output the low-side drive signal upon detecting that a switching stop period, during which the first voltage signal falls below a threshold voltage, exceeds a first period
Data Source
AI summary
A switching power supply controller, including a high-side drive circuit, a low-side drive circuit, a control circuit which supplies a high-side drive signal to the high-side drive circuit, and which supplies a low-side drive signal to the low-side drive circuit, an oscillation circuit which generates an on-trigger signal and an off-trigger signal at a switching frequency corresponding to a voltage signal, and which supplies the on-trigger signal and the off-trigger signal to the control circuit, and a precharge circuit which receives from the control circuit a burst operation signal, indicative of a burst operation in a standby mode, and which supplies for a second period a precharge signal that causes the control circuit to output the low-side drive signal upon detecting that a switching stop period, during which the first voltage signal falls below a threshold voltage, exceeds a first period.