Boost Converter ZCD Control Near Input-Output Voltage Crossover

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Solution Overview

Problem

In AC-DC applications, boost converters using zero current detection (ZCD) technology face instability when the AC input voltage is close to the output voltage, leading to unreliable detection and increased turn-on power loss.

Innovation Solution

A switching mode power supply with a control circuit that includes a zero crossing detector, a compare circuit, and a logical controller. The compare circuit shuts down the zero crossing detector when the AC input voltage is close to the output voltage, disabling the detect result and improving stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If zero current detection (ZCD) technology is used to improve conversion efficiency under discontinuous current mode, then turn-on power loss is reduced, but detection stability deteriorates when AC input voltage is close to output voltage

Engineering Contradiction:

Improveturn-on power lossVSAvoiddetection stability

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent implements dynamic control of the zero crossing detector by enabling it during normal operation and disabling it when AC input voltage approaches output voltage. The compare circuit dynamically adjusts the detector's operational state based on real-time voltage comparison, allowing the system to adapt between efficiency optimization and stability maintenance modes

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the operational parameter of the zero crossing detector from always-active to conditionally-active. By monitoring the voltage difference between AC input and output, the system adjusts the detector's enable/disable state, effectively changing its operational parameters to resolve the contradiction between efficiency and stability

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If valley switch-on technology is used to turn on main power switch at lowest voltage, then turn-on power loss is reduced, but detection reliability deteriorates when sensed voltage is very faint

Engineering Contradiction:

Improveturn-on power lossVSAvoidvoltage detection accuracy

Core Design Contradiction:

Loss of energyVSMeasurement precision

Solution Approach 1:

The patent introduces a compare circuit as an intermediary between the voltage sensing system and the zero crossing detector. This intermediary circuit compares the AC input voltage with the output voltage and generates control signals to disable the detector when voltage difference is minimal, thereby preventing unreliable detection in faint voltage conditions while preserving valley switch-on benefits in normal conditions

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS12308758B2Switching mode power supply with stable zero crossing detection, the control circuit and the method thereof

Publication Date: 2025.05.20 CHENGDU MONOLITHIC POWER SYST

AI summary

A switching mode power supply with stable zero crossing detection is discussed. The switching mode power supply disables a ZCD function when the AC input voltage has a voltage value close to a voltage value of the output voltage, so that instable zero crossing detection issues are eliminated. Meantime, when the AC input voltage has a voltage value close to a voltage value of the output voltage, the switching mode power supply turns on a main power after a dead time.