Flyback Converter Bridge Topology for Zero-Voltage Switching
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Solution Overview
Problem
Existing converter circuits for driving LEDs with d.c. input and output face challenges such as high voltage stress on switches, sensitivity to overvoltages, limited EMI reduction, and power leakage due to the absence of effective zero-voltage switching and the need for costly high-voltage components.
Innovation Solution
A converter device employing a bridge configuration with two switches and additional capacitances to facilitate zero-voltage switching, using a smaller MOSFET for energy recirculation and reduced reverse magnetizing current, and a control circuit to manage switch operations for efficient zero-voltage switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fly-back converter with single switch is used, then the circuit structure is simple, but the switch is exposed to very high voltage stress requiring costly high-voltage components
Solution Approach 1:
The patent divides the single high-voltage switch into two lower-voltage switches (Q1 and Q2) operating in a bridge configuration. Each switch only needs to withstand the bus voltage Vs rather than the sum of bus voltage plus transformed output voltage, allowing use of lower-voltage rated components.
Solution Approach 2:
The patent introduces an intermediary capacitor C1 connected between the primary winding and the bridge configuration. This capacitor enables zero-voltage switching by storing energy and providing a resonant path, allowing switches to turn on when voltage across them is zero, thereby reducing voltage stress and enabling use of lower-voltage switches.
2Ease of operation
If conventional switching is used, then the switching is straightforward, but electromagnetic interference is not effectively reduced
Solution Approach 1:
The patent implements periodic zero-voltage switching by using capacitor C1 to create resonant oscillations. The switches are turned on and off at specific periods when the voltage across them is zero, creating a periodic action that reduces electromagnetic interference while maintaining controlled switching operation.
Solution Approach 2:
The patent changes the switching parameter from voltage-driven switching to zero-voltage switching. By monitoring and switching when voltage across the switches is zero (rather than at arbitrary times), the patent reduces electromagnetic interference while maintaining ease of operation through controlled parameter changes.
3Reliability
If RCD snubber is used, then overvoltage protection is provided, but power leakage occurs due to dissipative elements
Solution Approach 1:
The patent replaces the dissipative RCD snubber with an intermediary capacitor C1 that enables reactive power recirculation. Instead of dissipating energy through resistors, the capacitor stores and releases energy, allowing overvoltage protection through zero-voltage switching without the power leakage inherent in RCD snubber circuits.
Solution Approach 2:
The patent recovers energy that would otherwise be dissipated. The capacitor C1 stores energy during switching transitions and returns it to the circuit, rather than allowing it to be dissipated as heat in RCD snubber resistors. This eliminates power leakage while maintaining overvoltage protection capabilities.
4Strength
If bridge configuration with zero-voltage switching is implemented, then voltage stress on switches is reduced and EMI is minimized, but device complexity increases
Solution Approach 1:
The patent makes the capacitor C1 serve multiple functions: it enables zero-voltage switching for both switches Q1 and Q2, provides overvoltage protection, and facilitates energy recirculation. This multi-functionality reduces the need for additional components, thereby limiting the increase in device complexity despite the bridge configuration.
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 reduces voltage stress on switches, achieves effective zero-voltage switching, minimizes electromagnetic interference, and optimizes energy usage, making the converter more efficient and cost-effective.
Implementation Method 1
A converter device employing a bridge configuration with two switches and additional capacitances to facilitate zero-voltage switching
Implementation Method 2
using a smaller MOSFET for energy recirculation and reduced reverse magnetizing current
Data Source
Figure 1~2
Figure 3~4
AI summary
A converter for generating a d.c. output signal (OS) starting from a stabilized input voltage (Vs) present on a bus line includes a flyback inductor (22) driven with a bridge structure that includes a first branch (34, Q2) and a second branch (Q1, Q3) with respective intermediate points (A, B) for driving the terminals of the flyback inductor (22). The first branch (34, Q2) includes a diode (34), which is set between the bus line and the intermediate point (A) of the first branch, as well as a first electronic switch (Q2), which acts between the intermediate point (A) and ground. The second branch (Q1, Q3) includes a second electronic switch (Q1), which acts between the bus line and the intermediate point (B), as well as a third electronic switch (Q3), which acts between the intermediate point (B) of the second branch and ground. A control unit (1000) is provided, which implements cyclically the sequence that includes: - a) bringing about a ramp-like increase of a magnetizing current in the flyback inductor (22) following upon activation of the first switch (Q2) and of the second switch (Q1); - b) de-activating the first switch (Q2) and the second switch (Q1) when the magnetizing current in the flyback inductor (22) reaches a given peak value; - c) activating the third switch (Q3), thus bringing about transfer of energy in the flyback inductor (22); and - d) activating the first switch (Q2) and de-activating the third switch (Q3) when the voltage on the first switch (Q2) has reached zero.