MOS transistor is widely used in switching power supply because of its low internal resistance and fast switching speed. The driver of MOS transistor often chooses the appropriate circuit according to the parameters of power IC and MOS transistor. When using MOS to design switching power supply, most people will consider the on resistance, maximum voltage and maximum current of MOS. But most of the time, only these factors are considered. Such a circuit may work normally, but it is not the best design.
In order to pursue MOS transistor more carefully, the parasitic parameters should be considered. For a certain MOS transistor, its driving circuit, peak current of the driver pin output, rising rate, etc., will affect its switching performance
Generally speaking, a good MOS driver circuit has the following requirements:
(1) When the switch is turned on, the driving circuit shall be able to provide enough charging current to make the voltage between MOS gate and source rapidly rise to the required value, so as to ensure that the switch can be turned on quickly and there is no high-frequency oscillation of rising edge.
(2) During the switching on period, the driving circuit can ensure that the voltage between MOS gate sources is stable and reliable.
(3) The instantaneous drive circuit can provide a path with the lowest impedance as far as possible for the fast discharge of the capacitor voltage between MOS gate and source, so as to ensure that the switch can be turned off quickly.
(4) The structure of the driving circuit is simple and reliable, and the loss is small.
There is no best driving circuit for all kinds of driving circuits, only combining with specific application to choose the most appropriate driver. When designing the power supply, we should consider how to design the drive circuit of MOS transistor from the above points of view. If we choose the finished power supply, no matter it is module power supply, general switching power supply, power adapter, etc., this part of work should be completed by the power supply designer.