Power Converter Control Circuit Reducing Touch Current
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Solution Overview
Problem
Power converters with power factor correction experience excessive touch current when leaving burst mode due to rapid voltage decrease of the input capacitor, which exceeds safety specifications, and existing solutions only partially address this issue by adjusting parameters.
Innovation Solution
A control circuit comprising an auxiliary pin, zero-crossing signal generator, feedback pin, frequency limiting signal generator, and gate signal generator, which generates a gate control signal with varying frequency based on compensation voltage between burst mode and quasi resonant mode reference voltages to reduce touch current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the power converter operates at the highest frequency when leaving burst mode, then the response speed is improved, but the touch current exceeds safety specification
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed high-frequency operation to a dynamically adjusted frequency. When leaving burst mode, the power converter initially operates at a reduced frequency to limit touch current, then gradually increases to the highest frequency as the input capacitor voltage decreases. This dynamic frequency adjustment resolves the contradiction between response speed and touch current safety.
Solution Approach 2:
The patent implements preliminary action by first reducing the operating frequency before the input capacitor voltage becomes dangerously low. This preliminary frequency reduction prevents the rapid voltage decrease that causes excessive touch current, allowing the system to safely transition to high-frequency operation later when the voltage has already stabilized at a safe level.
2Power
If the input capacitor voltage is quickly decreased to maintain high power output, then the power output is improved, but the touch current exceeds safety specification
Solution Approach 1:
The patent applies periodic action through a two-stage frequency transition process. First, a reduced frequency is applied during the initial transition from burst mode to prevent excessive touch current. Then, after the input capacitor voltage has decreased to a safe level, the frequency is increased to the highest level to maintain high power output. This periodic frequency adjustment resolves the contradiction between power output and touch current safety.
3Loss of energy
If the power converter operates in quasi resonant mode with high frequency, then the efficiency is improved, but the voltage decrease of input capacitor causes excessive touch current
Solution Approach 1:
The patent applies dynamics by making the operating frequency dependent on the input capacitor voltage level. During the transition from burst mode, the frequency is initially reduced to prevent excessive touch current even though this temporarily increases energy loss. Once the voltage has decreased to a safe level, the frequency is increased to the quasi resonant mode for improved efficiency. This dynamic adjustment resolves the contradiction between efficiency and touch current safety.
Data Source
AI summary
A control circuit for reducing touch current of a power converter includes an auxiliary pin, a zero-crossing signal generator, a feedback pin, a frequency limiting signal generator, and a gate signal generator. The auxiliary pin receives a voltage corresponding to an auxiliary winding of the power converter. The zero-crossing signal generator generates a zero-crossing signal according to the voltage and a first reference voltage. The feedback pin receives a feedback voltage corresponding to an output voltage of the power converter. The frequency limiting signal generator generates a frequency limiting signal according to the feedback voltage and a second reference voltage. The frequency limiting signal limits the gate control signal to a predetermined frequency. The gate signal generator generates a gate control signal to a power switch of the power converter according to the frequency limiting signal and the zero-crossing signal.