PWM Pulse Modification Circuit for EMI Reduction and Peak Power
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Solution Overview
Problem
Conventional switching power supplies experience significant electromagnetic interference (EMI) due to conducted and radiated emissions, requiring external filtering circuits and being inefficient at low temperatures, where electrolytic capacitors lose capacitance.
Innovation Solution
The circuit modifies pulse-width modulation (PWM) pulses by separating and shifting them in the time domain, increasing pulse count according to load requirements, and incorporating a temperature sensing unit to maintain functionality at low temperatures, thereby reducing EMI and enhancing peak power delivery without the need for large external filtering circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional PWM switching is used in switching power supplies, then power conversion is achieved, but electromagnetic interference (EMI) is generated through conducted and radiated emissions
Solution Approach 1:
The patent segments the continuous PWM switching waveform into multiple discrete pulse groups. By dividing the switching action into separate pulses with controlled timing, the energy that would otherwise concentrate into large EMI-generating spikes is distributed across multiple smaller events, reducing both conducted and radiated emissions while maintaining power conversion functionality
Solution Approach 2:
The patent implements periodic pulse groups with specific timing relationships. Pulses are arranged in periodic patterns where the timing and duration are controlled to achieve both power transfer and EMI reduction. The periodic structure allows predictable EMI characteristics that can be filtered more effectively while maintaining efficient power conversion
2Object-affected harmful factors
If external filtering circuits are added to reduce EMI, then electromagnetic compatibility is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies preliminary action by modifying the PWM waveform characteristics before the EMI generation occurs. By pre-shaping the pulses into groups with specific timing and duration, the source of EMI is reduced at its origin, thereby reducing or eliminating the need for complex external filtering circuits that would otherwise be required to achieve electromagnetic compatibility
3Quantity of substance
If electrolytic capacitors are used in switching power supplies, then energy storage is achieved, but capacitance is lost at low temperatures
Solution Approach 1:
The patent applies parameter changes by adjusting the PWM pulse parameters (width, frequency, grouping) in response to temperature conditions. When low temperature is detected, the controller modifies the pulse characteristics to compensate for the reduced capacitance, ensuring that the power supply maintains its functionality across a wide temperature range without requiring temperature-specific capacitor replacements
Data Source
AI summary
A circuit for electromagnetic interference (EMI) reduction contains a signal input, a signal output, a pulse count controlling unit, a stand-by power reduction unit, a pulse series delay unit, and a temperature sensing unit. An alternating current (AC) input is provided to the signal input and the modified signal is drawn out from the signal output. The pulse count controlling unit and the pulse series delay unit modify the pulses of the pulse-width modulation process such that the overall efficiency of the circuit is increased. In particular, the pulse count controlling unit increases the number of pulses per cycle such that additional power is transferred onto the output load. On the other hand, the pulse series delay unit shifts the start time of a series of pulses such that the overall emission is reduced. The stand-by power reduction unit disconnects power when a circuit overload occurs.