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B. RFI Choke - Minimizes spikes at output of supply by slowing down turn-on of triac.
C. Rectifier Damping Network - RC network protects other elements in supply against short-duration input
line transients.
D. Series Regulator Diode - Protects the series regulator against reverse voltages which could be delivered by
an active load or parallel power supply.
E. Slow Start Circuit - A long time-constant network that reduces turn-on overshoot and helps limit inrush
current. When supply is first turned on, this circuit holds off both the series regulator (to reduce output
overshoot) and the preregulator triac (to limit inrush current).
F. Amplifier Input Clamp Diodes - Limit the maximum input to the amplifier to protect it against excessive
voltage excursions.
G. Output Diode - Protects components in the power supply against reverse voltages that might be generated
by an active load or series connected power supply.
H. Sensing Protection Resistors - Protect the load from receiving full rectifier voltage if remote sensing leads
are accidentally open-circuited.
Figure 21. Protection Circuits, Linear Type Supply
Overcurrent and Overvoltage Protection - All Agilent supplies are short-circuit proof and can operate under any
current overload condition indefinitely without risk of internal damage. Overvoltage protection is also available
if required during constant current operation. The CV/CC and CV/CL automatic crossover circuitry discussed
previously is ideal for these purposes since it allows the user to select the maximum safe current or voltage for
the particular load device.
Overvoltage Crowbar - The crowbar circuit is connected across the output terminals, and provides protection
against any output overvoltage condition which might occur because of operator error or failure within the
power supply or load. Most Agilent power supplies of this type have either a built-in or optional crowbar
circuit. Because of its importance in many applications, the crowbar circuit is discussed in more depth on the
following pages.
Overvoltage Crowbar Circuit Details
An operator error or a component failure within the regulating feedback loop can drive a power supply's output
voltage to many times its preset value. The function of the crowbar circuit is to protect the load against this