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To avoid this problem, synchronous switching techniques are usually applied after the inductor current is at the DCM level.

It also causes current spike problems, making the control loop unstable and affecting THD. This switching sequence has a negative effect on the circuit. In this switch operation, the current path is maintained by discharging the output capacitor at the input source. In this section, a typical synchronous PWM triggers the switch even if the inductor current drops to zero around the zero crossing. The totem-pole PFC has a DCM current section at the zero crossing because of its driving method and circuit structure. In a typical totem-pole PFC, the high-frequency legs are operated in a synchronous PWM method to achieve high efficiency. In this paper, a digital control scheme for a GaN transistor-based totem-pole PFC is proposed. Therefore, there is a need for a synchronous PWM control technique to improve efficiency even at a low DCM current. In particular, the DCM current level must be higher for stable driving of GaN transistors with low gate source voltage (V GS) characteristics. To preclude this, a common approach is to operate in synchronous PWM mode when the inductor current increases above the DCM level. It also causes current spike problems, making the control loop unstable and affecting total harmonic distortion (THD). However, synchronous PWM operation triggers the switch even if the inductor current drops to zero around the zero crossing. To improve the efficiency of the PFC and reduce the heat generation in GaN transistors, synchronous PWM operation technology is generally applied. The solution to the current spike problems has been reported in many previous papers.

Typical problems include reverse operation due to current spikes and discontinuous conduction mode (DCM) of current.

The problem intensifies as the difference between low and high frequencies increases owing to the application of GaN transistors. Such a circuit configuration creates various problems near the zero crossing of the AC voltage. The totem-pole PFC is divided into low-frequency and high-frequency switching legs with line and switching frequencies, respectively.