Datasheet

TL05x, TL05xA
ENHANCED-JFET LOW-OFFSET
OPERATIONAL AMPLIFIERS
SLOS178A – FEBRUARY 1997 - REVISED FEBRUARY 2003
42
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
precision constant-current source over temperature
A precision current source (see Figure 85) benefits from the high input impedance and stability of Texas
Instruments enhanced-JFET process. A low-current shunt regulator maintains 2.5 V between the inverting input
and the output of the TL05x. The negative feedback then forces 2.5 V across the current-setting resistor R;
therefore, the current to the load simply is 2.5 V divided by R.
Possible choices for the shunt regulator include the LT1004, LT1009, and LM385. If the regulator’s cathode
connects to the operational amplifier output, this circuit sources load current. Similarly, if the cathode connects
to the inverting input, the circuit sinks current from the load. To minimize output current change with temperature,
R should be a metal film resistor with a low temperature coefficient. Also, this circuit must be operated with
split-voltage supplies.
+
–
+
–
150 pF
U2
+15 V
U1
–15 V
R
100 kΩ
I
O
Load
V = 0 to 10 V
(a) SOURCE CURRENT LOAD (b) SINK CURRENT LOAD
V = 0 to –10 V
Load
I
I
R
–15 V
U1
+15 V
150 pF
U2
100 kΩ
NOTE A: U1 = 1/2 TL05x
U2 = LM385, LT1004, or LT1009 voltage reference
I =
2.5 V
R
, R = Low-temperature-coefficient metal-film resistor
Figure 85. Precision Constant-Current Source