Isolated DC-DC Converter H-Bridge Common Mode Voltage Suppression
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Solution Overview
Problem
Isolated DC-DC converters face issues with parasitic capacitance leading to time-varying leakage currents across the isolation barrier, causing high-frequency radiation and electromagnetic interference, particularly in automotive and medical applications.
Innovation Solution
Incorporating symmetrical serial capacitors between the driver circuit and the primary winding of a transformer in the DC-DC converter to slow down common mode voltage variations, thereby reducing radiation emissions and improving electromagnetic interference (EMI) performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a driver drives a primary winding of a transformer to transmit power across an isolation barrier, then power transmission is achieved, but parasitic capacitance causes time-varying leakage currents and high-frequency radiation
Solution Approach 1:
A resonant circuit comprising a series capacitor and a series inductor is introduced as an intermediary between the full-bridge driver and the primary winding. This resonant circuit acts as a mediator that blocks the parasitic capacitance path, preventing leakage currents and high-frequency radiation while allowing power transmission through the transformer.
Solution Approach 2:
The patent changes the electrical parameters by introducing a resonant circuit with specific capacitance and inductance values that create a resonant frequency. This parameter change transforms the direct coupling path into a resonant path that operates at the desired frequency, blocking parasitic effects while maintaining power transmission efficiency.
2Object-generated harmful factors
If symmetrical serial capacitors are added between the driver and primary winding, then radiation emissions are suppressed and EMI performance improves, but device complexity increases
Solution Approach 1:
The series capacitor and series inductor are merged into a single resonant circuit unit that performs multiple functions: blocking parasitic capacitance, providing resonance at the operating frequency, and maintaining galvanic isolation. This consolidation reduces the perceived complexity compared to adding separate components for each function.
Solution Approach 2:
The resonant circuit serves multiple purposes simultaneously: it acts as a blocking capacitor for parasitic currents, provides resonant coupling for power transmission, and functions as an EMI filter. This multi-functionality justifies the added components by eliminating the need for separate circuits for each function.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively suppresses radiation emissions and enhances EMI performance by reducing common mode current across the isolation barrier, meeting or exceeding industry standards for EMI performance in various applications.
Implementation Method 1
a first capacitor coupled between the full bridge driver and the first terminal of the primary winding and a second capacitor coupled between the full bridge driver and the second terminal of the primary winding
Implementation Method 2
a driver that drives a primary winding of a transformer to transmit power to a secondary winding of the transformer across an isolation barrier
Data Source
AI summary
Isolated DC-DC converters and methods for operating the same are described herein. DC-DC converters include a driver that drives a primary winding of a transformer to transmit power to a secondary winding of the transformer across an isolation barrier. In some embodiments, a pair of symmetrical serial capacitors are provided between the driver and the primary winding of a resonant DC-DC converter with an on-chip transformer to slow down variations of a common mode voltage on the primary winding during operation. This in turn can suppress radiation emissions related to time variation rates of the common mode voltage and, and can also improve electromagnetic interference (EMI) performance of the DC-DC converter.