Offline Power Converter Dynamic Slew Rate Control for EMI and Surge Protection
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Solution Overview
Problem
Offline power supplies with slow current and voltage slew rates are ineffective in reacting quickly to high voltage surges, such as lightning or inductive voltage kicks, leading to potential system destruction due to inadequate EMI filtering.
Innovation Solution
An offline power converter design incorporating a normally-on power device, a power switch, first and second comparators, and a logic and drive unit that slowly turns off the power switch during normal operation but rapidly turns it off during surge events, utilizing distinct thresholds and a logic and drive unit to generate a slow-sloping or vertical ramp driving signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If slow current and voltage slew rates are used to reduce EMI filter size, then system cost is minimized, but the system cannot react quickly to high voltage surges
Solution Approach 1:
The patent implements dynamic control of the power switch by using a logic and drive unit that can generate different slew rates based on system conditions. During normal operation, the power switch transitions slowly to maintain low EMI, but during surge events detected by voltage comparators, the power switch transitions rapidly to protect the system. This dynamic adjustment of transition speed resolves the contradiction between EMI reduction and surge protection.
2Object-generated harmful factors
If slow slew rate is used during normal operation, then EMI is reduced, but the system fails to protect against destructive voltage spikes
Solution Approach 1:
The patent introduces voltage comparators and a logic and drive unit as intermediary components between the input voltage and the power switch. These intermediaries continuously monitor the input voltage and can rapidly activate the power switch to block surge events, while allowing slow slew rate operation during normal conditions to minimize EMI. This intermediary control mechanism enables the system to achieve both low EMI and high reliability.
3Reliability
If fast turning off of power switch is implemented, then surge protection is improved, but EMI increases and system cost increases
Solution Approach 1:
The patent applies different slew rate characteristics to different operating conditions through the logic and drive unit. During normal operation, the power switch uses slow slew rate to minimize EMI, but during surge events detected by the voltage comparators, the power switch rapidly transitions to provide protection. This localized application of different transition speeds based on system state resolves the contradiction between surge protection and EMI reduction.
Data Source
AI summary
An offline power converter provides low EMI and quick reaction by slowly turning off a power switch at normal operation, and fast turning off the power switch when surge event happens.