Voltage Mode Controller Short-Circuit Protection Flyback Converter

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Solution Overview

Problem

Existing voltage mode controllers in flyback power converters often falsely trigger short-circuited protection due to low detection voltages caused by light loads or valley areas in input DC voltage, leading to potential converter burn-down, especially during Limited Power Source tests.

Innovation Solution

A voltage mode controller with a gate control signal generation circuit and control circuit that generates a predetermined signal before startup and enables short-circuited protection based on detection and compensation voltages, with a de-bounce time consideration after startup, preventing false triggers and ensuring safe operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the short-circuited protection is enabled based on detection voltage alone, then the protection can detect actual short circuits, but it causes false triggers under light load conditions or valley areas of input DC voltage

Engineering Contradiction:

Improveshort-circuited protection accuracyVSAvoidfalse trigger of protection

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a compensation voltage as an intermediary parameter to mediate between the detection voltage and the protection trigger decision. The compensation voltage compensates for the detection voltage under light load conditions and valley areas, preventing false triggers while maintaining protection accuracy. This intermediary parameter allows the system to distinguish between actual short circuits and normal low-voltage operating conditions.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the parameter used for protection triggering from detection voltage alone to a combination of detection voltage and compensation voltage. By introducing the compensation voltage parameter and comparing it with a third reference voltage, the system dynamically adjusts the protection threshold based on operating conditions, thereby eliminating false triggers while maintaining reliable short-circuit detection.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If the voltage mode controller increases turning-on time of power switch in response to not receiving detection voltage, then the controller operates normally under light load, but it may cause the power converter to be burned down if short-circuited protection is not triggered

Engineering Contradiction:

Improvecontroller operation under light loadVSAvoidpower converter burn-down risk

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The compensation voltage serves as an intermediary that prevents the harmful effect of increased turning-on time under short-circuit conditions. When the detection resistor is short-circuited, the compensation voltage increases and triggers the protection mechanism, thereby preventing the power converter from being burned down while allowing normal operation under light load conditions.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent applies preliminary anti-action by enabling the short-circuited protection before the power converter can be damaged. The protection mechanism is designed to trigger when the compensation voltage exceeds the third reference voltage, preventing the harmful effect of continued operation under short-circuit conditions.

Inventive Principle:

Principle #9Preliminary anti-action

3Adaptability or versatility

If the detection resistor is short-circuited during LPS test, then the test can be executed, but the voltage mode controller cannot receive detection voltage and may operate abnormally

Engineering Contradiction:

ImproveLPS test execution capabilityVSAvoidcontroller operation reliability during test

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The compensation voltage acts as an intermediary that allows the controller to operate reliably during LPS tests. When the detection resistor is short-circuited during the test, the compensation voltage compensates for the missing detection voltage signal, enabling the controller to distinguish between test conditions and actual fault conditions.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS11290020B2Voltage mode controller applied to short-circuited protection of a power converter and operational method thereof

Publication Date: 2022.03.29 LEADTREND TECH

AI summary

A voltage mode controller applied to short-circuited protection of a power converter includes gate control signal generation circuit and control circuit. The control circuit generates control signal to make the gate control signal generation circuit generate predetermined signal to power switch of the primary side of the power converter before the power converter starts up and when supply voltage is greater than first reference voltage, enables short-circuited protection after predetermined enabling period of the predetermined signal if detection voltage is less than second reference voltage during the predetermined enabling period. The short-circuited protection makes the power converter not start up, and after the power converter starts up, the short-circuited protection is enabled to turn off the power converter if the detection voltage is less than the second reference voltage for de-bounce time and compensation voltage is greater than third reference voltage.