Datasheet

DataSheet

40W, Triple Output

VER:00 Page 33 of 40 Issued Date：2009/03/02

EMC Considerations (Continued)

This Common Choke L1 has beendefineas follows:

■

L1：450μH±35%/ DCR：25mΩ, max

Aheight：9.8mm, Max

■

L1：830μH±35%/ DCR：31mΩ, max

Aheight：8.8mm, Max

■ Test condition：100KHz / 100mV

■ Recommended through hole：Φ0.8mm

■ All dimensions in millimeters

Input Source Impedance

The power module sh

ould be connected to a low impedance input source. Highly inductive source impedance

can affect the stability of the power module. Input external L-C filter is recommended to minimize input reflected

ripple

current. The inductor has a source impedance of 12μH and capacitor is Nippon chemi-con KY series 220

μF/100V.

The capacitor must be located as closeas possible to the inputterminals of the powermodule for lowest impedance.

Output Over Current Protection

When excessive output currents occur in the

system, circuit protection is required on all power supplies. Normally,

overload currentis maintained at approximately 150 percent of rated current for PXF40-xxTxxxx series.

Hiccup-mode is a method of operation in a converter whose purpose is to protect

the power supply from being

damaged during an over-

current fault condition. It also enables the converter to restart when the fault is removed.

There are other ways of protecting the converter when it is over-loaded, such as the maximum current limiting o

current foldback methods.

One of the problems resulting from over current is that excessive heat may be generated in power devices;

especially MOSFET and Schottky diodes and the temperature of these devices may exceed their specified limits. A

protection mechanism has to be used to preventthesepower devices from beingdamaged.

The operation of hiccup is as follows. When the current sense circuit sees an over-

current event, the controller

shuts off the converter for a given time and then tries to start up the converter again. If the over-

load condition has

been removed, the converter will start up and operate normally; otherwise, the controller will see another over-

current

event and will shut off the converter again, repeating the previous cycle. Hiccup

operation has none of the drawbacks

of the other two protection methods, although its circuit is more complicated because it requires a timing circuit. The

excess heat due to overload lasts for only a short duration in the hiccup cycle, hence the junction

temperature of the

power devicesis muchlower.