Two Transistor Forward Converter Soft Transition Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The Two Transistor Forward topology suffers from high switching losses due to hard switching turn-on of primary and secondary switchers, leading to parasitic capacitance discharge and cross conduction losses, which negatively impact efficiency and introduce noise in power converter systems.
Innovation Solution
The method involves controlling the drive signal timing for SR1 and SR2 to achieve zero voltage switching for M1 and M2, actively shorting magnetizing inductance, and using a current source to inject a negative current through the freewheeling synchronous rectifier to discharge parasitic capacitances, thereby reducing switching losses and eliminating reverse recovery losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If hard switching turn-on is used for primary and secondary switchers, then the converter can operate with simple control, but switching losses increase and noise is introduced
Solution Approach 1:
The patent applies preliminary action by pre-charging the parasitic capacitances of the switchers before turn-on using a dedicated current source. This preparatory charging action eliminates the need for hard switching, as the capacitances are already charged when the switchers are activated, thereby reducing switching losses while maintaining operational simplicity
Solution Approach 2:
The patent introduces an intermediary current source circuit that actively manages the charging of parasitic capacitances. This intermediary component mediates between the power source and the switchers, providing controlled charge transfer that prevents energy loss during switching transitions while keeping the overall control scheme relatively simple
2Device complexity
If hard switching turn-on is used for primary and secondary switchers, then the converter structure remains simple, but cross conduction losses increase
Solution Approach 1:
The current source performs preliminary action by charging the parasitic capacitances before the switchers are turned on. This advance charging prevents cross conduction losses by ensuring that no sudden current discharge occurs through the body diodes when the switchers activate, thereby reducing energy loss without significantly complicating the converter structure
Solution Approach 2:
The patent converts the potentially harmful effect of parasitic capacitances into a beneficial feature. Instead of allowing these capacitances to cause cross conduction losses during hard switching, the invention uses a current source to deliberately charge them in advance, transforming what would be a source of loss into a controlled energy storage mechanism that actually improves efficiency
3Device complexity
If simple switching control is used, then the control circuit is simple, but parasitic capacitance discharge causes noise
Solution Approach 1:
The current source acts as an intermediary that controls the discharge path of parasitic capacitances. By providing a dedicated charging mechanism, it prevents uncontrolled discharge through the body diodes that would generate noise, thereby suppressing harmful electromagnetic interference while adding only moderate complexity to the control circuit
Solution Approach 2:
The patent replaces the passive mechanical switching action with an active electrical control mechanism. Instead of relying on simple on/off switching that causes abrupt capacitance discharge and noise, the invention uses a controlled current source to manage charge transfer, substituting uncontrolled electrical discharge with controlled charge injection, thereby reducing noise generation
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
This approach results in lower switching losses and reduced noise, enabling efficient resonant transitions with low leakage inductance, improving the overall efficiency of the power converter by allowing soft transitions and minimizing turn-on losses across switching elements.
Implementation Method 1
using a current source to inject a negative current through the freewheeling synchronous rectifier to discharge parasitic capacitances
Implementation Method 2
actively shorting magnetizing inductance
Implementation Method 3
the power is transferred to the secondary via SR1 and Lo. During that period of time, there is a forward energy transfer to the secondary
Data Source
AI summary
A method is shown to improve any forward topology operation to achieve efficient resonant transitions by actively shorting the magnetizing inductance and release the short at another time thus producing lower switching losses independent of frequency. In another embodiment of this invention the current from the output inductor is allowed to go negative before the freewheeling synchronous rectifier is turned off, pushing the current back into the primary to create a soft transition across the switching elements before they are turned on. In another embodiment of the invention a current source is used to inject a negative current through the freewheeling synchronous rectifier before is turned off with the purpose of transferring the current into the primary to discharge the parasitic capacitances of the primary switchers before are turned on. An optimized control method can be utilized to tailor the frequency to create the necessary conditions requested by the embodiments of the invention.