MAINTENANCE MANUAL
IFR 6000
2-2-1
Page 2
Aug 1/06
(3) Source Select Circuitry
The source select circuitry is designed to be a low-loss switch that selects the
appropriate source when the output of the ON/OFF circuitry is high. The external DC
(+Vdc) is selected if present. If external DC is not present, the battery (VBAT+)
connects to +VS. If the Test Set is running on external DC or Line Voltage, and that
power source is removed, the Test Set shuts OFF.
The second function of the switching circuitry is to prevent battery current from flowing
into the input converter section when the Test Set is running on battery power. A low
voltage cutoff is also incorporated into the ON/OFF circuitry.
(4) Protection Circuitry
The protection circuitry has four basic functions related to the DC input. The battery
has internal protection circuitry. The external DC input has a fuse, an over-voltage
crowbar and reverse protection diodes. The fuse is the primary disconnect to protect
against any of the fault conditions. If the DC input is too high (>32 V), the over-
voltage crowbar triggers and the SCR opens the fuse. If the DC input polarity is
incorrect, the input clamp diodes forward bias and open the fuse. If the input
converter fails and the output of the converter is above 12 V, the SCR triggers and
opens the fuse. If the DC input voltage is too low, the input converter is disabled until
the input voltage is within the allowable range.
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