Isolated Switch-Mode Power Supply Control Circuit for Shoot-Through Prevention
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Solution Overview
Problem
In isolated switch-mode power supplies operating in continuous conduction mode, the main power transistor experiences excessive current overshoot and a shoot-through phenomenon due to the freewheeling MOS transistor not being turned off in time, leading to reliability issues and Electro Magnetic Interference (EMI).
Innovation Solution
A control circuit with a current-limiting module and a driving circuit that gradually turns on the main power transistor, maintaining current at a predetermined value until the synchronous rectifier transistor is turned off, preventing excessive current flow and ensuring complete ON condition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the isolated switch-mode power supply operates in continuous conduction mode with conventional control, then the power supply can maintain continuous current flow, but the main power transistor experiences excessive current overshoot and shoot-through phenomenon
Solution Approach 1:
The control circuit performs preliminary action by detecting the current state of the secondary-side winding before turning on the main power transistor. The detection module monitors whether the current has reduced to zero, and only allows the main power transistor to be turned on after confirming the secondary-side current is zero, thereby preventing shoot-through phenomenon before it can occur
Solution Approach 2:
The control circuit implements feedback by using the detection module to continuously monitor the current state of the secondary-side winding and feed this information back to the control module. Based on this feedback, the control module dynamically adjusts the turn-on timing of the main power transistor, ensuring it is turned on only when safe to do so, thus preventing current overshoot and shoot-through
2Duration of action of moving object
If the freewheeling MOS transistor is not turned off on time, then the continuous conduction mode can be maintained, but excessive high current flows through the main power transistor causing shoot-through phenomenon
Solution Approach 1:
The control circuit performs preliminary detection of the secondary-side current state before allowing the main power transistor to turn on. By confirming the current is zero in advance, the system prevents harmful current overlap and shoot-through phenomenon while maintaining continuous conduction mode operation
Solution Approach 2:
The detection module monitors the natural current decay in the secondary-side winding, and the control module uses this information to precisely time the turn-on of the main power transistor. This converts the potential harmful overlap into a controlled transition, eliminating shoot-through while maintaining CCM operation
Data Source
AI summary
The present invention discloses an isolated switch-mode power supply, a control circuit and a control method thereof. The main power transistor and the synchronous rectifier transistor are connected respectively to the primary-side winding and secondary-side winding of the isolated switch-mode power supply. The voltage of the control terminal of the main power transistor starts to increase, the main power transistor is turned on gradually, the current flowing through the main power transistor starts to increase until reaches the predetermined current-limiting value; the current of the main power transistor is maintained at the current-limiting value by controlling the voltage of the control terminal of the main power transistor; the secondary-side synchronous rectifier transistor is turned off, the current of the main power transistor decreases from the current-limiting value to the normal operation value, and the main power transistor is completely in an ON condition.