Primary Side Controller for Isolated DC/DC Converter Surge Reduction
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Solution Overview
Problem
Isolated DC/DC converters face high surge voltages and increased current during startup or when the output is grounded, leading to high stress on components like the switching transistor and rectifier diode, resulting in increased costs due to the need for high withstand voltage designs.
Innovation Solution
A primary side controller with a low voltage state detecting circuit and pulse width modulator that adjusts the pulse signal period and ON/OFF times based on feedback signals to reduce current in the secondary winding during low voltage states, thereby reducing the stress on components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the switching transistor is designed with high withstand voltage to handle surge voltages during startup or ground fault, then the reliability is improved, but the cost increases
Solution Approach 1:
The control circuit detects low output voltage conditions (startup or ground fault) before surge voltages occur and preemptively adjusts the pulse signal period to extend the OFF time, preventing the harmful current buildup that would require high-withstand-voltage components
Solution Approach 2:
The pulse signal period parameter is dynamically changed based on output voltage detection - extending the period during low voltage conditions to control the secondary current slope, allowing standard-voltage components to handle transient conditions
2Object-generated harmful factors
If the pulse signal period is extended during low voltage states, then the current in secondary winding is reduced, but the productivity decreases
Solution Approach 1:
The pulse signal period is made dynamic rather than fixed - it automatically extends during low voltage states and returns to normal during steady-state operation, optimizing both transient protection and continuous power conversion efficiency
Solution Approach 2:
The control circuit uses feedback from output voltage detection to automatically adjust the pulse signal period, creating a closed-loop system that responds to actual operating conditions and optimizes performance across different states
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 solution effectively reduces the current in low voltage states, easing the voltage requirements for the switching transistor and allowing for lower-cost component selection and packaging, while maintaining efficient operation.
Implementation Method 1
a transformer T1 including a primary winding W1, a secondary winding W2, and an auxiliary winding W3
Implementation Method 2
a switching transistor M1 connected to the primary winding W1
Implementation Method 3
a secondary side rectifier circuit 202 configured to rectify a current flowing through the secondary winding
Data Source
AI summary
A primary side controller for controlling a switching transistor on a primary side of an isolated DC/DC converter, includes: a low voltage state detecting circuit configured to detect a low voltage state in which an output voltage of the DC/DC converter is lower than a predetermined value; and a pulse width modulator configured to generate a pulse signal whose ON time is adjusted depending on a feedback signal from a secondary side, wherein a period of the pulse signal in the low voltage state is longer than a period of the pulse signal in a non-low voltage state in which the output voltage is higher than the predetermined value.