Datasheet

Feb.2006
7
20W,
DUAL
OUTPUT
Output over current protection
Whenexcessive output currents occur in the system, circu
it protection is required on all power supplies.Normally,
overload current ismaintained at approximately 150 percent ofrated current forPXD20-xxDxx series.
Hiccup-mode is a method of operation in a power supply whose purpose is to protect the power sup
ply from
being damaged during an over-
current fault condition. It also enables the power supply to restart when the fault is
removed. There are other ways of protecting the power supply when it is over-
loaded, such as the maximum current
limiting or currentfoldbackmethods.
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 those devices may exceed their specified limits. A
protection mechanism has to beused to prevent those powerdevices from being damaged.
The operation of hiccup is as follows. When the current sense circuit sees an over-
current event, the controller
shuts off the powersupply for a given time and then tries tostart up the power supply again.If the over-
load condition
has been removed, the power supply will start up and operate normally; otherwise, the controller will see another
over-current event and shut off the power supply again, repeating the previous cycle. Hiccup o
peration 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 thepower devices is much lower.
Short Circuit Protection
Continuous, hiccup and auto-recovery mode.
During short circuit, the converter still shut down.The average current during this condition will be verylow .