Datasheet
TEP 75WI Series
Application Note
http://www.tracopower.com Page 58 of 69
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 percent of rated current for TEP 75WI 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 specied 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 Circuitry 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.
Output Over Voltage Protection
The output over-voltage protection consists of circuitry that monitors the voltage on the output terminals. If the voltage on the output
terminals exceeds the over-voltage protection threshold, then the module enter the non-latch hiccup mode.
Over Temperature Protection
Sufcient cooling is needed for the power module and provides more reliable operation of the unit. If a fault condition occurs, the
temperature of the unit will be higher. And will damage the unit. For protecting the power module, the unit includes over-temperature
protection circuit. When the temperature of the case is to the protection threshold, the unit enters “Hiccup” mode. And it will auto
restart when the temperature is down.