AN-9066

APPLICATION NOTE

Discontinuous Current Mode Power

Factor Correction

Generally, power factor correction circuits have used a

boost topology because it is simple and low costs. There are

two modes of the power factor correction boost circuit

operation. One is continuous current mode (CCM) that has

continuous inductor current. This mode has many benefits,

like lower core loss and ripple current and a smaller input

filter; but it requires very fast reverse recovery diode as the

boost diode since the boost switch in being switched on

while the inductor current is not zero. The discontinuous

current mode switches on the boost switch when the

inductor current is zero, allowing less expensive diodes to

be used. The turn-on loss of the boost switch is also

negligible. Usually, the discontinuous current mode is used

for small power supplies, 300W or less, that have relatively

small inductor current, but are very sensitive to cost

constraints.

Simulation and Experimental

Results

is clearly stated in datasheets, but the switching loss varies

greatly by the circuit conditions. To compare the switching

performance in the system, one UniFET and one super-

junction device are selected and evaluated. An inductive

switching test board was used to measure switching loss at

turn-off transient. In this way, it is possible to keep the

important test variables, like drain current and external

series gate resistor, under control.

Figure 1 shows the energy loss curves with different

conditions of the series gate resistor and the drain-current.

The solid traces indicate the losses of the UniFET and the

dotted traces are losses of the super-junction device. There

are four different lines per device, according to the pre-set

drain current levels. The drain current levels are 20A, 10A,

6.5A, and 1.8A from top to bottom.

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© 2009 Fairchild Semiconductor Corporation

www.fairchildsemi.com

Rev. 1.0.1 • 4/3/09

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