Reactiveloads - Keithley 7169 Instruction Manual

2.7.4 Reactive Loads
Since reactive loads can cause excessive currents and voltages, current
surge limiting (for capacitive loads) and voltage clamping (for inductive
loads) are required to prevent damage to relays and external circuitry.
Capacitive Loads
The surge current from a capacitive load must be <0.5A for the Model
7169 to protect the relays and circuit board. Figure 2-9 shows typical cir-
cuits to limit current surges. Also, consider the maximum load of 1OW
for the Model 7169 when determining the current limit. For example,
when switching 1OOV with the Model 7169, the current must be limited
to:
I = VA/V = lOVA/lOOV = lOOmA
The current limiting resistor as used in Figure 2-9A would be:
R = V/I = lOOV/lOOmA = lkn 0 1OW
A. Resistor Limited
, High reSiSla"Ce VAlsn Cold.
LOW mSiSta"Ce wile" hot.
FaStthslmsl recovery.
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B. Thermistor Limited
Figure 2-9. Limiting Capacitive Renction Current
2-19