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AN103

Siliconix
Part Number AN103
Manufacturer Siliconix
Description The FET Constant-Current Source/Limiter
Published Jan 19, 2007
Detailed Description www.DataSheet4U.com AN103 The FET Constant-Current Source/Limiter Introduction The combination of low associated opera...
Datasheet PDF File AN103 PDF File

AN103
AN103

Overview
www.
DataSheet4U.
com AN103 The FET Constant-Current Source/Limiter Introduction The combination of low associated operating voltage and high output impedance makes the FET attractive as a constant-current source.
An adjustable-current source (Figure 1) may be built with a FET, a variable resistor, and a small battery.
For optimum thermal stability, the FET should be biased near the zero temperature coefficient point.
D S RL RS – + A change in supply voltage or a change in load impedance, will change ID by only a small factor because of the low output conductance goss.
DID = (DVDS)(goss) (3) The value of goss is an important consideration in the accuracy of a constant-current source where the supply voltage may vary.
As goss may range from less than 1 mS to more than 50 mS according to the FET type, the dynamic impedance can be greater than 1 MW to less than 20 kW.
This corresponds to a current stability range of 1 mA to 50 mA per volt.
The value of goss also depends on the operatin...


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