关键词: Buck型变换器, DC-DC电路, 抗振铃, 阻尼电阻

Abstract: The current of the inductor connected outside may drop to zero when the buck converter has a smaller load. In order to prevent the buck converter enter into FCCM and the current direction of inductor reversed which results in the discharge of the load capacitor through the free-wheeling NMOS and the reduction of the DC-DC conversion efficiency, we design the protection circuit detecting the voltage of the inductor front-end when the current dropped to zero. If the voltage is greater than zero, it forces to shut off the NMOS switch and the buck converter enters into DCM. The parasitic capacitor of the switch MOS form the LC oscillation circuit with the inductor outside and generate the ringing phenomenon. In order to restrain the ringing phenomenon, this article designs control circuit to insert a damping resistor to reduce the parallel resistor of the capacitor, which accelerates the attenuation of the oscillation.

Key words: Buck converter, DC-DC circuit, anti-ringing, damping resistance