Totem-Pole PFC Switch Control for Low-Voltage Hard Turn-On
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Solution Overview
Problem
In totem-pole power factor correction circuits, hard turn-on of the switching transistor occurs due to low input voltage, leading to increased switching losses and reduced efficiency, especially when the auxiliary power switch is turned on with different voltages on both sides.
Innovation Solution
A control circuit is implemented that controls the main and auxiliary power switches in a half-bridge circuit, turning on the main power switch and keeping the auxiliary switch off when the input voltage is within a predetermined phase range and below a certain voltage threshold, and alternately turning on both switches when the voltage exceeds this threshold, thereby reducing switching losses and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the auxiliary power switch is turned on when input voltage is low, then the circuit can operate during low voltage periods, but hard turn-on occurs causing increased switching losses
Solution Approach 1:
The control circuit dynamically adjusts the operating parameters of the auxiliary power switch based on the input voltage level. When the input voltage is below a threshold, the control circuit prevents the auxiliary switch from turning on, avoiding hard turn-on conditions. This parameter-based control strategy resolves the contradiction by adapting the switch operation to the instantaneous voltage conditions, eliminating excessive switching losses while maintaining circuit functionality during normal voltage periods
Solution Approach 2:
The control circuit continuously monitors the input voltage level and uses this feedback information to make real-time decisions about auxiliary power switch operation. The feedback mechanism detects when the input voltage falls below the threshold and accordingly disables the auxiliary switch, preventing hard turn-on events. This closed-loop control ensures the circuit operates efficiently across varying voltage conditions without incurring excessive switching losses
2Adaptability or versatility
If the auxiliary power switch is turned on with different voltages on both sides, then the circuit can handle voltage differences, but switching efficiency decreases due to hard turn-on
Solution Approach 1:
The control circuit implements parameter-based control that adapts to the instantaneous voltage conditions across the auxiliary power switch. By monitoring the voltage difference between both sides of the switch and adjusting the switch operation accordingly, the circuit maintains adaptability to handle voltage differences while preventing hard turn-on events that would reduce switching efficiency. The control circuit dynamically modifies the switching parameters based on real-time voltage measurements
Solution Approach 2:
The control circuit applies preliminary anti-action by preventing the auxiliary power switch from turning on when voltage differences exist that would cause hard turn-on conditions. Before the harmful hard turn-on event can occur, the control circuit detects the unfavorable voltage conditions and proactively disables the switch operation. This preventive approach maintains the circuit's ability to handle voltage differences while preserving switching efficiency by avoiding detrimental switching events
Data Source
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AI summary
Embodiments of this application provide a power module, a totem-pole power factor correction circuit, and a control circuit thereof. In response to a case in which a phase value of a transient voltage of an input voltage of the totem-pole power factor correction circuit is within a predetermined phase range, and an absolute value of a voltage value is less than a predetermined voltage value, the control circuit controls a main power switch in the totem-pole power factor correction circuit to be turned on and off, and controls an auxiliary power switch to remain off. According to embodiments of this application, turn-on in a case of different voltages at both sides of the auxiliary power switch may be avoided when the voltage value of the input voltage is small. Therefore, a switching loss is reduced, and operating efficiency of the totem-pole power factor correction circuit and a power module including the totem-pole power factor correction circuit is improved.