Bootstrap Circuit Switching for Stable PFM Bias Power
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Solution Overview
Problem
The PFM mode in power converters leads to instability in the bootstrap capacitor voltage due to insufficient charging during high impedance states, causing unnecessary switching losses and inefficiency in bias power supply.
Innovation Solution
A switched capacitor bootstrap circuit and an active bootstrap circuit are employed to provide bias power in high impedance PFM mode and other operating modes, respectively, using flying capacitors and auxiliary switches to maintain stable voltage without intermittent switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the power converter operates in PFM mode with high impedance state, then switching losses are reduced, but the bootstrap capacitor voltage becomes unstable
Solution Approach 1:
The patent implements a dynamic bootstrap circuit that automatically switches between two operating modes: in PWM mode, the circuit operates in charging mode to rapidly recharge the bootstrap capacitor; in PFM mode, it operates in leakage compensation mode to maintain stable voltage. This dynamic adaptation resolves the contradiction by optimizing the bootstrap circuit behavior according to the power converter's operating mode, reducing switching losses in PFM while ensuring voltage stability.
2Stability of the object's composition
If the low-side switch is periodically turned on to recharge the bootstrap capacitor, then the bootstrap voltage stability is improved, but unnecessary switching losses occur
Solution Approach 1:
The patent employs a self-service mechanism where the bootstrap circuit automatically detects the power converter's operating mode and adjusts its behavior accordingly. In PFM mode, the circuit enters leakage compensation mode that actively maintains bootstrap capacitor voltage without requiring periodic low-side switch activation. This self-adjusting mechanism eliminates unnecessary switching losses while ensuring voltage stability, as the circuit serves itself by adapting to operational conditions.
3Device complexity
If a traditional bootstrap circuit is used in PFM mode, then the circuit structure remains simple, but the bias power supply efficiency deteriorates
Solution Approach 1:
The patent enhances the traditional bootstrap circuit by adding dynamic control capabilities that enable automatic mode switching. The circuit incorporates detection mechanisms that identify whether the power converter is in PWM or PFM mode, and accordingly switches between charging mode and leakage compensation mode. This dynamic enhancement maintains relatively simple circuit structure while dramatically improving bias power supply efficiency in PFM mode by preventing bootstrap capacitor voltage collapse.
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 reduces switching losses and maintains stable bias power in PFM mode, improving efficiency while minimizing additional component costs and chip area.
Implementation Method 1
a bootstrap capacitor Cbst connected between a bootstrap voltage bus BST, and a common node of the high-side switch Q1 and the low-side switch Q2
Implementation Method 2
The diode D1 and the bootstrap capacitor Cbst form a bootstrap circuit configured to provide bias power for the first driver 101 and the auxiliary circuits 110
Data Source
AI summary
A control circuit includes a first multiplexer having a first input configured to receive a PWM voltage and a second input configured to receive a clock signal voltage, a second multiplexer having a first input configured to receive a bias voltage and a second input configured to receive an output voltage of a power converter, a flying capacitor and a diode connected in series between an output of the first multiplexer and an output of the second multiplexer, a third multiplexer selectively coupling a common node of the flying capacitor and the diode or the output of the second multiplexer to a first terminal of an auxiliary switch, and the auxiliary switch having a gate connected to the common node, the first terminal coupled to an output of the third multiplexer, and a second terminal configured to be coupled to a bootstrap capacitor of the power converter.