Circuit Project Electronic

A low-drift voltage reference can be easily made by converting a zero temperature coefficient current to a voltage. JFETs biased slightly below pinch-off exhibit a zero temperature coefficient drain current (ID) as shown in Figure 1. With the above property and a micropower operational amplifier, used to convert the drain current to a voltage, a low power consumption voltage reference can be built as shown in Figure 2. The consumption of LM4250 op amp is programmed through resistor RSET. Potentiometer P1 should be adjusted for low output (VREF) temperature coefficient.

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http://www.national.com/an/LB/LB-34.pdf