Synchronous Rectifier Circuit with Auxiliary Charging Loop
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Solution Overview
Problem
Conventional rectifier devices, such as diodes, consume significant power due to the 0.7V voltage drop when conducting large currents, and synchronous rectifier controllers face challenges in operating with low output power voltages from power converters, which are often below the required 5V for proper operation.
Innovation Solution
A rectifier circuit with a rectifier switch, auxiliary switch, and operating power capacitor, where the rectifier controller manages the switches to support two loops for charging and rectification, using demagnetization time to build up the operating power voltage independently of the power converter's output, ensuring the rectifier circuit can operate even with low input voltages by charging the capacitor during demagnetization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a diode is used for rectification, then the rectifier circuit is simple, but the power consumption is high due to 0.7V voltage drop
Solution Approach 1:
The patent changes the operating parameters of the rectifier by using a synchronous rectifier switch instead of a diode. The rectifier switch can be turned on to have very low impedance, reducing the voltage drop from 0.7V to nearly zero, thereby significantly reducing power consumption while maintaining rectification function
Solution Approach 2:
The patent replaces the passive diode with an active rectifier switch controlled by a rectifier controller. This substitution allows the system to actively control the rectification process, turning the switch on during forward bias to minimize voltage drop and off during reverse bias to block current, thus reducing energy loss
2Device complexity
If the output power voltage is used to supply the rectifier controller, then the circuit is simple, but the operating power voltage is insufficient when output voltage is low (3.5V)
Solution Approach 1:
The patent segments the voltage supply function by introducing a separate operating power voltage generation path independent of the output power voltage. The operating power capacitor is charged during demagnetization time through a dedicated charging loop, ensuring the rectifier controller receives sufficient voltage (≥5.5V) regardless of the output voltage level
Solution Approach 2:
The patent introduces an auxiliary winding and operating power capacitor as intermediary elements between the transformer and the rectifier controller. During demagnetization, the auxiliary winding generates voltage to charge the operating power capacitor, which then supplies stable operating voltage to the rectifier controller, isolating it from fluctuations in output power voltage
3Loss of energy
If the rectifier switch is turned on to reduce impedance, then power consumption is reduced, but the operating power voltage cannot be built up when output voltage is low
Solution Approach 1:
The patent employs periodic action by utilizing the demagnetization time period to charge the operating power capacitor. During this specific time window when the main rectifier switch is off, the auxiliary switch is turned on to charge the operating power capacitor from the auxiliary winding, ensuring operating voltage is built up without affecting the low-impedance rectification path during the on-time
Solution Approach 2:
The patent performs preliminary action by charging the operating power capacitor during demagnetization time before the next rectification cycle begins. This ensures that the rectifier controller has sufficient operating voltage ready in advance, preventing voltage insufficiency issues that would occur if the output voltage alone was used to supply the controller
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 allows the rectifier circuit to maintain an operating power voltage above 5.5V, even when the output power voltage is as low as 3.5V, enhancing power conversion efficiency and ensuring reliable operation across a wide voltage range.
Implementation Method 1
using demagnetization time to build up the operating power voltage independently of the power converter's output
Data Source
AI summary
A rectifier circuit has a cathode node, an anode node, a rectifier switch, an auxiliary switch, an operating power capacitor and a rectifier controller supplied with power by the operating power capacitor. The rectifier switch is electrically connected to the auxiliary switch. When the rectifier controller turns OFF both the rectifier and auxiliary switches, the rectifier circuit supports a first loop, directing a first current to flow into the rectifier circuit from the anode node, through the operating power capacitor, and away the rectifier circuit from the cathode, so the operating power capacitor is charged. When the rectifier controller turns ON both the rectifier and auxiliary switches, the rectifier circuit supports a second loop directing a second current to flow into the rectifier circuit from the anode node, through the rectifier switch, and away the rectifier circuit from the cathode, without charging the operating power capacitor.