Flyback Converter Active Clamping Control for Zero Voltage Switching
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Solution Overview
Problem
Existing flyback power converter circuits with active clamping face issues such as prolonged ON time of the auxiliary switch leading to high power loss and inadequate discharge of parasitic capacitors, resulting in non-zero voltage switching during primary switch activation, especially at high input voltages.
Innovation Solution
The flyback power converter circuit incorporates an adjustable ON time for the auxiliary switch controlled by current-related signals, input voltage, and output voltage to ensure zero voltage switching of the primary side switch, utilizing a conversion control circuit that includes an auxiliary switch control circuit, signal sensing circuit, and sequence control to manage the switching times and frequencies for efficient power conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the auxiliary switch S2 switches complementarily with the primary side switch S1, then the energy stored in parasitic inductances can be transferred to the auxiliary capacitor Cr, but the ON time of the auxiliary switch may be too long causing large circulation current and high power loss
Solution Approach 1:
The patent applies dynamics by making the ON time of the auxiliary switch variable rather than fixed. The control circuit dynamically adjusts the ON time based on real-time detection of voltage and current conditions, allowing the system to optimize the balance between energy transfer and circulation current reduction under different operating conditions.
Solution Approach 2:
The patent implements feedback by using a control circuit that detects voltage and current signals and uses this information to adjust the auxiliary switch's ON time. This closed-loop control ensures the auxiliary switch operates optimally by responding to actual circuit conditions, preventing both excessive circulation current and insufficient energy transfer.
2Reliability
If the ON time TON2 of the auxiliary switch S2 is set as a constant time period, then the control is simplified, but when input voltage is high, the ON time may not be long enough to fully discharge the parasitic capacitor Coss, preventing zero voltage switching
Solution Approach 1:
The control circuit uses feedback from voltage and current detection to dynamically determine the auxiliary switch's ON time. This ensures that under high input voltage conditions, the auxiliary switch remains ON long enough to fully discharge the parasitic capacitor and achieve zero voltage switching, while avoiding excessive ON time under lower voltage conditions.
Solution Approach 2:
The patent changes the parameter of auxiliary switch ON time from a fixed constant to a variable parameter that adapts to different operating conditions. By adjusting this parameter based on detected voltage and current levels, the system achieves reliable zero voltage switching across varying input voltages without requiring overly complex control logic.
3Reliability
If the auxiliary switch ON time is extended to ensure full discharge of parasitic capacitor at high input voltages, then zero voltage switching can be achieved, but circulation current increases causing higher power loss
Solution Approach 1:
The control circuit continuously monitors voltage and current conditions and adjusts the auxiliary switch's ON time accordingly. This feedback mechanism ensures the minimum necessary ON time is provided to achieve zero voltage switching while avoiding excessive ON time that would cause high circulation current and power loss.
Solution Approach 2:
The system dynamically adapts the auxiliary switch's ON time to match actual operating conditions rather than using a fixed extended duration. This dynamic adjustment ensures zero voltage switching is achieved when needed while minimizing circulation current and power loss by reducing the ON time when conditions permit.
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 ensures zero voltage switching of the primary side switch, enhancing power conversion efficiency by dynamically adjusting the auxiliary switch's ON time based on real-time voltage and current conditions, thereby reducing power loss and maintaining efficient operation across varying input voltages.
Implementation Method 1
the parasitic capacitor Coss of the primary side switch S1 can be discharged by the energy stored in the auxiliary capacitor Cr
Implementation Method 2
a transformer, which includes a primary side winding coupled to an input power and a secondary side winding coupled to an output node
Data Source
AI summary
A flyback power converter circuit includes: a transformer including a primary side winding coupled to an input power and a secondary side winding coupled to an output node, wherein the input power includes an input voltage; a primary side switch coupled to the primary side winding for controlling the input power to generate an output power on the output node through the secondary side winding, wherein the output power includes an output voltage; a clamping circuit including an auxiliary switch and an auxiliary capacitor connected in series to form an auxiliary branch which is connected with the primary side winding in parallel; and a conversion control circuit for adjusting an ON time of the auxiliary switch according to at least one of a current related signal, the input voltage, and the output voltage, such that the primary side switch is zero voltage switching when turning ON.