AN-9066

APPLICATION NOTE

In Figure 5, an IR camera was used to measure device

temperature. Three measurement points are a PFC diode and

two paralleled PFC MOSFETs. Even with small gate

resistor, the UniFET temperature is lower than the super-

junction device by around 10 degrees. The reason for this

lower temperature is smaller switching losses, as shown in

Figure 6. The UniFET switching-off energy loss at the peak

of AC input voltage is less than a half of the super-junction

device switching loss. There is a little plateau in the drain

current of the super-junction that makes switching-off loss

bigger. There was no such waveform in the bench test.

Perhaps it is due to different gate drive circuitry and printed

circuit board layout.

Recently,

dedicated

controllers

for

the

interleaved

discontinuous current mode power factor correction were

introduced to the market. The interleaved CRM PFC

technique is a good alternative solution to implement high-

density, cost-effective converters with an extended input

power range. It quickly became mainstream topology in

switching power supplies for flat panel displays because the

interleaving technique can reduce the total system cost

compared to CCM topology. Although it requires a pair of

boost inductors, boost switches, and rectifiers, it can use

small-sized

filters,

smaller

high-voltage

aluminum

electrolytic capacitor, a less-expensive 500V-rated boost

switches, and slower rectifiers. In addition, making the flat

panel TV slim is a trend and the smaller components are a

crucial requirement for a low-profile switching power

supply.

As the interleaving PFC is also operated in discontinuous

current mode, the UniFET can be quite competitive with the

super-junction device. To compare system performance, the

UniFET and the super-junction device were tested with an

interleaved DCM PFC evaluation board. The evaluation was

done using an interleaved CRM controller with phase

management. Two RURP860 ultrafast rectifiers are applied

as

boost

diodes.

The

test

conditions

are

set

as

room

temperature without fan, and an external bias for controller

supply voltage.

(a) Super-Junction Device

(b) UniFET

™

Figure 5. Device Temperature (Not Same Scale)

(a) Super-Junction Device

(b) UniFET

™

Figure 6. Switching-Off Energy Loss

© 2009 Fairchild Semiconductor Corporation

www.fairchildsemi.com

Rev. 1.0.1 • 4/3/09

5