DC-DC Converter Clamping Circuit for Fast PFM to PWM Mode Transition
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Solution Overview
Problem
Conventional DC-to-DC converters face inefficiencies in rapidly switching from pulse frequency modulation (PFM) mode back to pulse width modulation (PWM) mode when load conditions change, due to an unfavorable voltage gap between ramp and comparison voltages, which prolongs the transition time.
Innovation Solution
Incorporating a clamping circuit that is disabled in PWM mode and enabled in PFM mode to allow the comparison voltage to follow the ramp voltage, reducing the voltage gap and enabling rapid switching back to PWM mode when load conditions become heavy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the DC-to-DC converter operates in PFM mode with a large voltage gap between ramp and comparison voltages, then energy efficiency is improved for light-load conditions, but the switching speed back to PWM mode deteriorates
Solution Approach 1:
The patent applies dynamics by making the clamping circuit's connection state changeable based on operating mode. In PFM mode, the clamping circuit is disconnected to allow large voltage gap and high efficiency. In PWM mode, the clamping circuit is connected to clamp the comparison voltage to follow the ramp voltage, enabling fast switching. This dynamic reconfiguration resolves the contradiction between energy efficiency and switching speed.
Solution Approach 2:
The patent changes the voltage relationship parameter between comparison voltage and ramp voltage based on operating mode. In PFM mode, the voltage gap is maintained large for efficiency. In PWM mode, the clamping circuit forces the comparison voltage to track the ramp voltage, changing the voltage relationship to enable fast response. This parameter change resolves the contradiction.
2Speed
If the clamping circuit is enabled to make comparison voltage follow ramp voltage, then switching speed to PWM mode is improved, but circuit complexity increases
Solution Approach 1:
The clamping circuit acts as an intermediary element that can be selectively activated. It provides the necessary voltage tracking function during mode transition without permanently complicating the circuit. The switching control of the clamping circuit allows it to serve its purpose only when needed, minimizing its impact on overall circuit complexity while achieving fast switching speed.
3Stability of the object's composition
If the clamping circuit is disabled to allow independent comparison and ramp voltages, then PWM mode operation is maintained, but transition speed from PFM mode deteriorates
Solution Approach 1:
The clamping circuit is activated in advance before the mode transition is complete, preparing the comparison voltage to track the ramp voltage. This preliminary action reduces the transition time by having the voltage relationship ready before full PWM operation begins, thus reducing the loss of time during mode switching.
Data Source
AI summary
A DC-to-DC converter and a PWM device thereof are provided. The PWM device includes a ramp generator circuit, an error amplifier, a comparator and a clamping circuit. The error amplifier compares a voltage difference between the feedback voltage and the reference voltage to output a comparison voltage corresponding to the voltage difference. The comparator compares a ramp voltage of the ramp generator circuit and the comparison voltage of the error amplifier, so as to output a pulse signal. The clamping circuit determines whether to induce the comparison voltage to follow the ramp voltage. The clamping circuit is disabled when the PWM device is operated in the PWM mode, such that the comparison voltage and the ramp voltage are independent of each other. The clamping circuit is enabled when the PWM device is operated in the non-PWM mode, such that the comparison voltage follows the ramp voltage.