Keithley 6220, Reference Manual

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3-4 DC Current Source Operation Model 6220/6221 Reference Manual
Return to Section 3 topics
When operating as a sink, the Model 622x is dissipating power rather than sourc-
ing it. The polarity of the current and voltage seen at the output is opposite (one
positive, one negative). An external source or an energy storage device, such as a
capacitor, can force operation into the sink region.
Figure 3-1 shows examples of the Model 622x connected to an external source
where it can operate as a source or sink. For both examples, the Model 622x is
programmed to 10mA. When connected to the 1k
Ω
resistor and 10V
source as shown in Figure 3-1 A, the Model 622x operates as a 200mW source
supplying power to the external test circuit. When the external voltage is
decreased to -30V as shown in
Figure 3-1 B, the Model 622x instead operates as
a sink. The Model 622x dissipates 200mW of power (10mA x -20V = -200mW).
Figure 3-1
Source and sink examples
Operating boundaries
Figure 3-2 shows the four quadrants of operation for the Model 622x. When oper-
ating in the first (I) or third (III) quadrant, the Model 622x is operating as a source.
Figure 3-1 A shows an example of quadrant I operation (current and voltage both
positive).
When operating in the second (II) or fourth (IV) quadrant, the Model 622x is oper-
ating as a sink.
Figure 3-1 B shows an example of quadrant IV operation (current
positive and voltage negative).
1k W
20V
622x
+10mA
A) Source operation
1k W
-20V -30V
622x
+10mA
B) Sink operation
10mA 10mA
10V
Hi
Lo
Hi
Lo
10V 10V
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