Current Sources and Voltage References

The cascode DMOS current source

Creating Medium-Power Current Sources with DMOS FETs

197

load impedance will cause only a very small change in current as a result of the output

conductance (g

os

), as shown by:

In the same example, if the particular DMOS FET device had a g

os

value of 100 µS, a

constant current of I

D

of 10 mA, and a ∆V

DS

of 500 mV change occurred, then the out-

put current would change by only 50 µA (0.005%), which is pretty good.

Table 7.1 lists applicable

depletion-mode vertical DMOS FETs from Supertex and Sili-

conix (Vishay). These are mostly low-cost devices and are available in a wide range of

packages, including metal-can, plastic, ...