Issues to be aware of when using power MOSFET in switching power supplies

The following issues should be noted when power MOSFET is used in switching power supplies.

(1) The impedance of the gate circuit is very high and is easily damaged by static electricity.

(2) The DC input impedance is high, but the input capacity is large. The input impedance is low at high frequencies. Therefore, the drive circuit impedance needs to be reduced.

(3) High-frequency oscillations are likely to occur when working in parallel.

(4) When conducting, the current surge is large, which can easily lead to overcurrent.

(5) In many cases, it cannot be used as is in the self-oscillation circuit of a bipolar transistor.

(6) The reverse recovery time of the parasitic diode is long, which in many cases is unbalanced with the switching speed of the field effect transistor.

(7) The fast switching speed generates noise, which can easily cause the drive circuit to malfunction, especially when the switching method is a bridge circuit and the power supply of the gate circuit is floating.

(8) The capacitance between drain and gate is extremely large, and changes in drain voltage can easily affect the input.

(9) With the addition of negative feedback, the thermal stability is also better than that of bipolar transistors, but this effect cannot be achieved when used in cases where the current value is small.

(10) Theoretically, there is no current concentration to cause secondary breakdown, but the parasitic transistor is damaged by du/dt, and thus the field effect transistor is also damaged.