Bridgeless PFC Control Circuit Zero Current Detection
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Solution Overview
Problem
Conventional bridgeless PFC circuits face challenges in reducing switch loss and effectively detecting the zero-crossing point of inductor current, which affects their efficiency and operation in critical conduction control mode.
Innovation Solution
A control circuit and method that includes a zero current detection circuit, feedback circuit, and pulse distribution circuit to detect the polarity of the input voltage and generate a driving pulse signal, enabling the switch in the bridge arm to turn on under zero voltage, thereby reducing switch loss and reliably detecting the zero-crossing point of the inductor current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the second MOSFET is controlled to be turned on when the voltage decreases to zero to reduce switch loss, then switch loss is reduced, but the complexity of control mechanism increases
Solution Approach 1:
The patent introduces an auxiliary winding on the inductor as an intermediary element. This auxiliary winding generates a voltage signal that automatically indicates when the inductor current reaches zero, eliminating the need for complex control mechanisms to detect the zero-crossing point. The auxiliary winding acts as a mediator between the inductor current state and the control circuit, providing a simple voltage signal that triggers the MOSFET turn-on at the optimal moment.
Solution Approach 2:
The control circuit uses the voltage signal from the auxiliary winding to automatically determine when to turn on the second MOSFET. The system serves itself by using the inductor's own voltage characteristics (reflected in the auxiliary winding) to control the switching timing, without requiring external complex control mechanisms or additional sensing circuits.
2Device complexity
If a simple and effective method is used to detect the zero-crossing point of inductor current, then detection simplicity is improved, but measurement precision may be compromised
Solution Approach 1:
The auxiliary winding serves as an intermediary that transforms the difficult-to-measure inductor current zero-crossing point into an easily detectable voltage signal. When the inductor current reaches zero, the auxiliary winding voltage also reaches zero, providing a clear and precise detection point without requiring complex measurement circuits.
Solution Approach 2:
The patent replaces direct current measurement (which would require complex sensing circuits) with voltage signal detection from the auxiliary winding. This substitution of measurement method maintains high detection precision while significantly simplifying the detection circuit.
Data Source
AI summary
A control circuit, control method used in a PFC circuit and the power source system thereof are disclosed herein. The control circuit comprises: a zero current detection circuit having a polarity detection circuit for outputting a first and a second digital signals and a signal conversion circuit for generating an analog signal; a feedback circuit for generating a driving pulse signal; and a pulse distribution circuit for distributing the driving pulse signal to a first and a second switches according to the first and the second digital signal. After a switch cycle, one of the first and the second switch performs an ON operation for the next switch cycle when the current flowing through the inductor decreases to a predetermined threshold value, wherein an ON time of the first switch is equal in each switch cycle, and an ON time of the second switch is equal in each switch cycle.