PWM Oscillator Frequency Control via Current Scaling

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Solution Overview

Problem

PWM controllers face challenges in accurately controlling minimum and maximum frequencies due to the sensitivity of oscillation current levels to noise and the increased size required for higher capacitance to achieve low frequencies, making it difficult to prevent mode changes from boundary conduction mode to continuous conduction mode.

Innovation Solution

An oscillator with sourcing and sinking currents N times larger than the oscillation current, combined with a 1/N frequency divider, is used to generate an oscillation frequency within a target range, allowing precise control of frequencies and enabling an oscillation holding operation to prevent mode changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If higher capacitance is used to achieve low frequencies, then the oscillation frequency can be reduced to the target range, but the oscillator size increases

Engineering Contradiction:

Improveoscillation frequencyVSAvoidoscillator size

Core Design Contradiction:

SpeedVSVolume of moving object

Solution Approach 1:

The patent changes the current parameter instead of the capacitance parameter. By using sourcing and sinking currents that are N times larger than the oscillation current, the system achieves the same low frequency effect without needing large capacitance values, thus maintaining a compact oscillator size while achieving the target frequency range

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a frequency divider as an intermediary component. The oscillator generates a high-frequency signal, and the frequency divider reduces it to the target frequency range. This allows the oscillator itself to remain small while still achieving low output frequencies through the intermediary frequency division process

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If oscillation holding operation is implemented to prevent mode changes, then the reliability is improved, but the device complexity increases

Engineering Contradiction:

Improvemode change preventionVSAvoidcontrol circuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the oscillation holding function with the existing frequency divider and current switching infrastructure. The same sourcing and sinking currents used for frequency generation are repurposed for the holding operation, and the control logic is integrated into the existing oscillation control structure. This merging approach enables reliable mode change prevention without proportionally increasing device complexity

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS10523184B2Oscillator, method of operating the same, and PWM controller including the same

Publication Date: 2019.12.31 SEMICON COMPONENTS IND LLC

AI summary

An oscillator for a pulse width modulation (PWM) controller includes an oscillation circuit including a capacitor and configured to generate a first pulse signal by charging and discharging the capacitor, a frequency divider configured to generate a second pulse signal based on the first pulse signal, the second pulse signal having a lower frequency than the first pulse signal, and an oscillation control circuit coupled to the oscillation circuit and the frequency divider and configured to generate control signals for holding the charging and discharging of the capacitor during an oscillation holding operation.