Switch-off delay generates a shutdown current, vout/L* delay time.
I1R=This voltage.

[1] Deng Chaoxuan. Design of synchronous rectified BUCK type DC-DC zero-crossing detection circuit [D]. Southwest Jiaotong University, 2014.


[1] Yan Ermei, Wei Yuanwu, Guo Tao, Yang Jun. A zero-crossing detection circuit suitable for synchronous rectifier switching power supply [J]. Application of Electronic Technology, 2013, 39(08): 47-49+53.DOI: 10.16157/j.issn.0258-7998.2013.08.007.
A zero-crossing detection circuit suitable for synchronous rectifier mode switching power supply is proposed. This circuit converts the leakage voltage signal of the synchronous rectifier tube into a current signal and compares the current with the bias current to determine whether the current is zero during the free flow of the synchronous rectifier tube. Since the linearization resistor is used to convert voltage to current by using transistors of the same type as rectifier tube, the impact of the rectifier tube resistance with temperature and process changes on the zero crossing detection accuracy in traditional zero crossing detection circuits is eliminated. Based on the 0.6μm CD process, the designed circuit was simulated and verified. The simulation results show that the circuit can achieve high-precision zero-crossing detection within a given process and temperature fluctuation range, which has strong robustness, and the power consumption of the circuit is only 6μA.

Applicable objects:
According to the analysis of the synchronous rectification theory in Chapter 2, when using synchronous rectification devices, since MOS is a bidirectional conduction device, it may cause the inductor current to flow in reverse and finally flow into the battery, causing damage to the battery. Therefore, a zero-cross detection (zero_cross) circuit is added to the circuit to detect the voltage across the synchronous rectifier tube to prevent the reverse flow of current.