REV. C

REF01

–8–

PRECISION CURRENT SOURCE

A current source with 25 V output compliance and excellent

output impedance can be obtained using this circuit. REF01

keeps the line voltage and power dissipation constant in the

device; the only important error consideration at room temperature

is the negative supply rejection of the op amp. The typical 3

µV/

V PSRR of the OP02E will create an 8 ppm change (3 V/V

25 V/10 V) in output current over a 25 V range. For example, a

10 mA current source can be built (R = 1 k

Ω) with 300 MΩ

output impedance.

R

V

mA

××

−

25

810

10

6

GND

REF01

GND

REF01

OP02E

R

(TRIM FOR

CALIBRATION)

C

C

R

2

2

2

6

6

7

3

4

6

4

4

+50V

–5V

TO +25V

+10V

R

Figure 10. Precision Current Source

SUPPLY BYPASSING

For best results, it is recommended that the power supply pin is

bypassed with a 0.1

µF disc ceramic capacitor.

REFERENCE STACK WITH EXCELLENT LINE

REGULATION

Three REF01s can be stacked to yield 10.000 V, 20.000 V, and

30.000 V outputs. An additional advantage is near-perfect line

regulation of the 10.0 V and 20.0 V output. A 32 V to 60 V

input change produces an output change that is less than the

noise voltage of the devices. A load bypass resistor (RB) provides

In general, any number of REF01s can be stacked this way. For

example, 10 devices will yield outputs of 10, 20, 30 . . . 100 V.

The line voltage can change from 105 V to 130 V. However,

care must be taken to ensure that the total load currents do not

exceed the maximum usable current (typically 21 mA).

GND

REF01

GND

REF01

GND

REF01

TRIM

TRIM

10k

10k

6.8k

10k

2

6

5

4

2

6

5

4

2

6

5

4

TRIMMED

OUTPUTS

30.000V

20.000V

10.000V

32V TO 60V

TRIM

Figure 11. Reference Stack