Datasheet
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 kΩ) with 300 MΩ
output impedance.
R
V
mA
O
=
××
−
25
810 10
6
V
IN
GND
REF01
V
O
V
IN
GND
REF01
V
O
OP02E
R
(TRIM FOR
CALIBRATION)
C
C
R
2
2
2
6
6
7
3
4
6
4
4
+50V
–5V
V
O
= 0
TO +25V
I
O
=
+10V
R
RC = 10
–5
SEC
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
a path for the supply current (I
SY
) of the 20.000 V regulator.
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).
V
IN
GND
REF01
V
O
V
IN
GND
REF01
V
O
V
IN
GND
REF01
V
O
TRIM
TRIM
10k
10k
R
B
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