Buck-Boost Pass-Through Mode with Periodic Bootstrap Refresh
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Solution Overview
Problem
Buck-boost converters experience under voltage protection due to voltage drops across bootstrap capacitors when high-side switches are maintained ON, leading to abnormal operation.
Innovation Solution
Implement a control circuit with a bootstrap refresh mechanism that periodically generates a refresh clock signal to control power switches, ensuring timely charging of bootstrap capacitors and preventing undervoltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the first high-side switch Q1 and the second high-side switch Q4 both adopt an N type transistor, then the switching performance is improved, but the bootstrap capacitor voltage drops causing under voltage protection and abnormal operation
Solution Approach 1:
The patent implements a periodic refresh mechanism for the bootstrap capacitor voltage. The control circuit periodically charges the bootstrap capacitors during specific switching intervals, ensuring the voltage is maintained at adequate levels. This periodic action prevents the voltage drop that would otherwise trigger under-voltage protection and cause abnormal operation, while allowing the N-type transistors to maintain their superior switching performance.
2Productivity
If the first high-side switch Q1 and the second high-side switch Q4 are maintained ON in pass through mode, then the voltage transmission efficiency is improved, but the bootstrap capacitor voltage drops causing under voltage protection
Solution Approach 1:
Even in pass-through mode where high-side switches are generally maintained ON for efficient voltage transmission, the control circuit periodically initiates refresh cycles for the bootstrap capacitors. This periodic refreshing ensures that the bootstrap capacitor voltage does not drop below the threshold that would trigger under-voltage protection, thereby maintaining both high transmission efficiency and reliable operation.
Solution Approach 2:
The control circuit monitors the state of the bootstrap capacitors and uses feedback control to determine when refreshing is needed. This feedback mechanism allows the system to maintain high-side switches in the ON state for efficient voltage transmission while periodically intervening to recharge the bootstrap capacitors, preventing under-voltage conditions without continuously disrupting the pass-through operation.
Data Source
AI summary
A buck boost converter with pass through mode is discussed. The buck boost converter may operate at buck mode, boost mode, buck-boost mode, and pass through mode based on different input voltage and output voltages. A control circuit periodically controls the power switches to operate at a refresh mode when the buck boost converter operates at the pass through mode. Thus, the bootstrap voltages that are used to drive the N-type power switches are timely charged.