KEPCO BHK-MG 200W (Full Rack) Series - Manual (Page 27)

BHK-MG (OPR) 022014
1-11
h. Current Limit. The current through the main branch of the pass element is monitored. If this
current is maintained between 1.8 to 2.2 times larger than the nominal value for more than
11ms, the pass element is latched off, the output capacitor is discharged, and the POWER
circuit breaker is tripped to OFF.
1.4.11 CURRENT SINK CAPABILITY
BHK-MG 200W Series power supplies are able to sink up to 5% of the nominal current when in
voltage mode and 50% of the unit's maximum rated current when in current mode. The fixed
current mode sink value is model dependent and has a tolerance of 10%. Since negative cur-
rent is not displayed on the front panel meter, it is transparent to the user when the unit enters
sink mode.
This capability is useful in applications such as capacitor testing, where the sink capability
allows the rapid discharge of the device under test, permitting subsequent tests to be started
earlier, thus increasing the throughput of the testing process.
The sink current in current mode is quite stable, allowing this feature to be used with the dis-
charging process to determine the value of a capacitor under test by measuring the discharge
time, using the formula C = T x I / V (the charge time, which is more accurate, can also be used
in the formula), where
T = discharge or charge time
V = change in voltage from fully charged to fully discharged, or vice versa.
I = discharging or charging current (BHK-MG charging current has a tolerance of
0.05% of nominal value, discharge current has a tolerance of 10% of nominal value)
The value of the capacitor under test can be calculated directly by measuring T and either using
the above formula and the appropriate tolerance for I, or by comparing T to that of a known
capacitor value.
Once the capacitor under test completely discharges, current from the power supply’s internal
current generator will flow through the output protection diode (or, in some models, multiple
diodes), resulting in a slight reverse voltage at the output which will be clamped to the value of
the voltage drop across the diode(s).