JF48S5-3000 Datasheet, PDF (4/15 Pages) Wall Industries,Inc. – DC/DC Converter

TECHNICAL DATASHEET
JF48S5-3000
DESIGN CONSIDERATIONS:
Output Over Current Protection
When excessive output currents occur in the system, circuit protection is required on all power supplies.
Normally, overload current is maintained at approximately 110~140% of rated current for the JF Series.
Hiccup-mode is a method of operation in a power supply whose purpose is to protect the power supply 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 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 those devices may exceed their specified limits.
A protection mechanism has to be used to prevent those power devices 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 power supply for a given time and then tries to start 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
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 devices is much lower.
The hiccup operation can be done in various ways. For example, one can start hiccup operation any time an over-
current event is detected; or prohibit hiccup during a designated start-up is usually larger than during normal
operation and it is easier for an over-current event is detected; or prohibit hiccup during a designated start-up
interval (usually a few milliseconds). The reason for the latter operation is that during start-up, the power supply
needs to provide extra current to charge up the output capacitor. Thus the current demand during start-up is
usually larger than during normal operation and it is easier for an over-current event to occur. If the power
supply starts to hiccup once there is an over-current, it might never start up successfully. Hiccup mode protection
will give the best protection for a power supply against over current situations, since it will limit the average
current to the load at a low level, so reducing power dissipation and case temperature in the power devices.
Short Circuit Protection
Continuous, hiccup and auto-recovery mode.
During short circuit, converter still shut down. The average current during this condition will be very low and
the device can be safety in this condition.
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