Instruction manual

Document: MAN00238A Page 24 of 28
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10. FAULTS / TROUBLESHOOTING
Faults
Overcurrent: If the output becomes shorted or if there is a surge in output current due to changes in
the load that exceed the rated current, then this circuit will be tripped. Its threshold is
set by R137. Once this circuit is tripped, HV is latched off. The power supply will
give a fault indication by lighting the ‘Fault’ LED permanently. The ‘HV ON’ light
will go out as well. This tells the user to correct the load and reactivate HV.
Both overload (or overcurrent) circuits are driven by a buffered current feedback
signal that is derived from a shunt resistor located in the high voltage section of the
power supply.
Overvoltage: Overvoltage is a fault which will rarely be tripped. Adjustable via R69, this circuit
will be activated when it senses output voltage which is greater than the set point. An
unstable system, due to load dynamics, may cause an overvoltage condition. This
circuit is driven by a buffered voltage feedback signal derived from the HV divider.
This fault will cause HV to be latched off and the Fault LED will light.
dV/dt: (Change in Voltage per Change in Time) The source of a fault of this type is an
output arc, which causes a very large change in voltage in a short period of time.
This circuit is also driven by the voltage feedback. Like the fast OL fault, this type of
fault causes a rollback, which will not place the supply in a latched fault condition. It
merely temporarily interrupts high voltage so the condition can clear. The output
then recovers to the set point with little indication. The purpose for this type of
recovery is that permanent shutdowns or faults can become a nuisance when arcing is
a common occurrence in high voltage systems.
The dV/dt circuit is not adjustable.
AC Overload: The AC OL fault is the average primary current or "Avg OL" fault, which is more
sensitive when the unit is operating closer to its rated output voltage and current. It is
a slower responding circuit than the peak circuit and its main purpose is to limit
power output by triggering rollbacks. Sensitivity is adjusted via R41.
The AC OL fault circuits are non-latching. They act to keep the primary current in
the HV transformer from reaching excessive levels.
Rail Fault: This circuit protects against excessively large current in the power inverter, which
may or may not be related to the primary current signal. However, the rail fault
circuit is used to protect against more catastrophic events than the typical output
conditions the primary current circuits were designed to withstand.
An imbalance in the voltage sharing of the power switches or a failed power switch
might be the cause of a rail fault. Thus, you will rarely (if ever) see this type of
latched fault. Like the other latched faults, this circuit will illuminate the Fault LED.
The sensitivity of this circuit is adjustable via R165.