Synchronous Rectifier Forward Converter Reverse Current Suppressor
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Solution Overview
Problem
Synchronous rectifier forward converters experience reverse current issues and voltage spikes during shutdown due to delayed turn-off of the freewheel switch, leading to potential damage to power semiconductor devices.
Innovation Solution
A reverse current suppressor is introduced to detect the shutdown of the forward converter and send a turn-off signal to the freewheel switch, either through an enable signal from internal circuitry or by detecting voltage changes across the secondary winding, ensuring timely turn-off of the freewheel switch to prevent reverse current and voltage spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the synchronous rectifier uses transistors instead of diodes to reduce conduction loss, then power loss is reduced and efficiency is improved, but the risk of reverse current and voltage spikes increases during shutdown
Solution Approach 1:
The reverse current suppressor detects the shutdown state of the forward converter and proactively sends a turn-off signal to the freewheel switch before reverse current can occur. This preliminary action prevents the harmful reverse current and voltage spikes from developing, thereby protecting the power semiconductor devices while maintaining the efficiency benefits of using transistors in the synchronous rectifier
2Ease of operation
If the freewheel switch is allowed to conduct during normal operation to provide current path, then the synchronous rectifier functions properly, but the switch fails to turn off timely during shutdown causing reverse current
Solution Approach 1:
The reverse current suppressor continuously monitors the operational state of the forward converter and uses this feedback information to control the freewheel switch. When shutdown is detected, the suppressor immediately sends a turn-off signal to the freewheel switch, ensuring timely discontinuation of current conduction and preventing reverse current flow that would otherwise damage the devices
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 reverse current suppressor effectively suppresses reverse current and voltage spikes, protecting power semiconductor devices by ensuring timely turn-off of the freewheel switch during shutdown, thereby improving the reliability and efficiency of the synchronous rectifier forward converter.
Implementation Method 1
The magnetizing inductance of the primary winding of the transformer is configured to receive the current from the voltage input terminal of the forward converter and store energy therein, and transfer the stored energy to the secondary side of the transformer according to the on/off operations of the main switch
Implementation Method 2
The energy stored in the primary side of the transformer T1 is transferred to the secondary side of the transformer T1 according to the on/off operations of the main switch Q1, and thereby inducing an AC voltage across the secondary winding Ns
Data Source
AI summary
Disclosed is a synchronous forward converter having a reverse current suppressor connected to the gate of a freewheel switch. The reverse current suppressor is configured to receive a control input signal generated by an internal circuitry of a power supply system where the forward converter locates, such as an enable signal, to detect the power-off of the forward converter, and in response thereto turn off the freewheel switch during the interruption of the input power of the forward converter. Alternatively, the reverse current suppressor is configured to detect the decay of the input voltage across the input bulk capacitor located on the primary side of a transformer of the forward converter, and turn off the freewheel switch when the voltage across the secondary side of the transformer is decayed to be smaller than the output voltage of the forward converter.