PFM Startup Control for Switching Power Supply Converters
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Solution Overview
Problem
Switched mode power supplies face challenges during start-up, particularly in efficiently managing energy accumulation and restitution phases, often requiring complex circuitry and continuous energy cycles, which can be energy intensive and inefficient.
Innovation Solution
A voltage converter operating in pulse frequency modulation (PFM) mode during start-up, utilizing a series connection of MOS transistors, an inductor, and capacitors, with control circuits to manage energy accumulation and restitution phases, ensuring positive inductor current and avoiding negative current, thus reducing energy consumption and simplifying start-up processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If continuous energy cycles are used during start-up, then energy accumulation and restitution can be maintained, but energy consumption increases and start-up time extends
Solution Approach 1:
The patent implements periodic energy accumulation and restitution cycles during start-up, where the converter operates in PFM mode with alternating phases of energy storage in the inductor and energy release to the output capacitor. This periodic action ensures reliable energy transfer while allowing the system to remain in low-power state between cycles, reducing overall energy consumption compared to continuous operation.
Solution Approach 2:
The patent applies preliminary action by pre-charging the output capacitor through a dedicated start-up circuit before the main converter begins regular operation. This preliminary energy accumulation reduces the burden on the main converter during initial start-up, allowing it to begin energy cycles at a lower power level and gradually increase, thereby reducing total energy consumption during the start-up phase.
2Reliability
If complex circuitry is used for start-up control, then precise energy management can be achieved, but device complexity increases
Solution Approach 1:
The patent implements self-service by using the converter's own output voltage to control its start-up sequence. The control circuit monitors the output capacitor voltage and automatically adjusts the switching duty cycle and frequency based on the charging state, eliminating the need for external complex control circuits. The system manages its own energy accumulation and restitution phases through intrinsic feedback from the output voltage level.
Solution Approach 2:
The control circuit performs multiple functions using a single integrated design: it generates the switching signals for the MOS transistors, monitors the output voltage, determines the energy accumulation phase duration, controls the energy restitution phase, and manages the transition from start-up to steady-state operation. This multi-functionality reduces device complexity compared to having separate dedicated circuits for each control function.
3Reliability
If PWM circuitry is used, then precise control of energy phases can be achieved, but the device becomes unsuitable for low-power applications
Solution Approach 1:
The patent employs parameter changes by dynamically adjusting the switching frequency and duty cycle based on the converter's operating state. During start-up, the converter operates in PFM mode with variable frequency that adapts to the energy requirements at each moment. This allows precise control of energy accumulation and restitution phases without the continuous high-frequency switching required by PWM, thereby reducing power consumption while maintaining control precision.
Solution Approach 2:
The control system is designed to be dynamic, transitioning from PFM mode during start-up to other operating modes during steady-state. The switching parameters (frequency and duty cycle) are continuously adjusted based on the output voltage level and load conditions. This dynamic adaptation allows the converter to achieve precise energy phase control when needed while operating in lower-power modes during stable operation, making it suitable for low-power applications.
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
The PFM mode reduces energy intensity, shortens the start-up phase, and eliminates the need for a clock signal or error amplifier, enabling efficient and rapid converter initialization while maintaining positive inductor current, suitable for low-power devices without PWM circuitry.
Implementation Method 1
a supply potential, supplied to an input of the switched mode power supply, is chopped by switching MOS (Metal Oxide Semiconductor) transistors in such a way as to implement phases of energy accumulation in an inductive element or inductance and phases of restitution, to a load connected to the output of the switched mode power supply, of the energy accumulated in this inductive element
Implementation Method 2
a supply potential, supplied to an input of the switched mode power supply, is chopped by switching MOS (Metal Oxide Semiconductor) transistors
Implementation Method 3
the fourth output node being connected to the second node for applying the second reference voltage by a first capacitor
Data Source
AI summary
The present disclosure relates to a voltage converter and method for pulse frequency modulation-type operation during a start-up phase.