Switched Mode Power Supply Clamp Diode Failure Prevention
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Solution Overview
Problem
Phase-shifted full-bridge DC/DC converters face issues with clamp diode failure due to excessive voltage stress and dynamic losses during load transients, particularly at small loads, where the existing clamp diode solution is inadequate, leading to potential converter destruction.
Innovation Solution
Incorporating load elements in series with clamp diodes to reduce the reset time of the resonant inductor current, using resistors or diode-resistor combinations to increase the reset voltage and speed, and implementing a power outage detection system to differentiate between AC outages and load transients, thereby preventing false trips and ensuring efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If clamp diodes are used to protect against voltage overshoot and ringing, then voltage stress on rectifier diodes is reduced, but the clamp diodes fail during load transients at small loads due to excessive current and heating
Solution Approach 1:
The protection function is segmented between two types of diodes: fast recovery diodes for normal voltage clamping during steady-state operation, and ultra-fast recovery diodes specifically for protecting against transient conditions during load changes. This segmentation allows each diode type to be optimized for its specific function, resolving the contradiction between steady-state protection and transient reliability.
Solution Approach 2:
The invention changes the recovery time parameter of the clamp diodes by using two different diode types with different recovery characteristics. Fast recovery diodes (with longer recovery time) handle steady-state voltage clamping, while ultra-fast recovery diodes (with shorter recovery time) handle transient conditions. This parameter change resolves the contradiction by matching diode characteristics to operational conditions.
2Loss of energy
If dead time delay is added between switches to allow voltage commutation, then switching losses are reduced, but the converter response time during load transients increases
Solution Approach 1:
The dead time delay is made dynamic rather than fixed. The control system adjusts the dead time duration based on operating conditions: longer dead time during steady-state to minimize switching losses, and shorter dead time during load transients to improve response speed. This dynamic adjustment resolves the contradiction between energy efficiency and response speed.
Solution Approach 2:
The system uses feedback from load current sensing to dynamically adjust the dead time parameter. When load transients are detected, the feedback mechanism reduces the dead time delay, allowing faster response while still maintaining adequate voltage commutation. This feedback-based adaptation resolves the contradiction by optimizing dead time for current operating conditions.
Data Source
AI summary
Generally, a DC/DC converter and its associated devices and processes are presented herein. The DC/DC converter may be a switched mode converter that includes a plurality of switching devices that couple between the first and second power supply rails. A transformer is coupled to the switching devices such that the switching devices exchange electrical energy through the transformer. A rectifier is coupled to the transformer to rectify the waveform from the transformer into a substantially DC output. The DC/DC converter also includes clamp diodes to relieve voltage stress on rectifier diodes. Resistors may be coupled in series with the clamp diodes to reduce a reset time of the DC/DC converter and thereby prevent catastrophic failure of the power supply during load transients. Additionally, the DC/DC converter may be configured with a power outage detection device that monitors gate drive signals of the converter.