### ETC AB-006

```APPLICATION BULLETIN
®
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Make a –10V to +10V Adjustable Precision Voltage Source
By R. Mark Stitt, (602) 746-7445
Many situations require a precision voltage source which
can be adjusted through zero to both positive and negative
output voltages. An example is a bipolar power supply.
0V, then swapped the output leads and adjusted it back up to
get a negative voltage output? What happened to your circuit
when the input from the low impedance source went open
circuit? Were you able to actually adjust the output to 0V, or
did a small voltage offset limit the range? This precision
bipolar voltage source can solve these problems.
However, a simpler solution is to use a single voltage
reference and a precision unity-gain inverting amplifier. If
you use a precision difference amplifier for the unity-gain
inverting amplifier, the circuit requires just two chips and a
potentiometer.
To understand how the circuit works, first consider the –
1.0V/V to +1.0V/V linear gain control amplifier shown in
Figure 1. An INA105 difference amplifier is used in a unitygain inverting amplifier configuration. A potentiometer is
connected between the input and ground. The slider of the
pot is connected to the noninverting input of the unity-gain
inverting amplifier. (The noninverting input of a unity-gain
inverting amplifier would normally be connected to ground.)
With the slider at the bottom of the pot, the circuit is a
normal precision unity-gain inverting amplifier with a gain
of –1.0V/V ±0.01% max. With the slider at the top of the
pot, the circuit is a normal precision voltage follower with a
gain of +1.0V/V ±0.001% max. With the slider in the center,
there is equal positive and negative gain for a net gain of 0V/
V. The accuracy between –1.0V/V and +1.0V/V will normally be limited by the accuracy of the pot. Precision 10turn pots are available with 0.01% linearity.
Perhaps the most obvious implementation of a bipolar voltage source would be to use a bipolar voltage reference.
INA105
Difference Amp
2
VIN
5
R1
25kΩ
10kΩ
Linear
3
R2
25kΩ
R3
25kΩ
6
VOUT =
+V IN to –V IN
The –1.0V/V to +1.0V/V linear gain control amplifier has
many applications. With the addition of a precision +10.0V
reference as shown in Figure 2, it becomes a –10V to +10V
1
R4
25kΩ
VOUT = +VIN, Slider at Top of Pot.
VOUT = 0V, Slider at Center of Pot.
VOUT = –VIN, Slider at Bottom of Pot.
FIGURE 1. –1.0V/V to +1.0V/V Linear Gain Control Amplifier.
+VS
2
V+
INA105
Difference Amp
REF102
10V 6
Out
2
Gnd
4
VOUT = +10V, Slider at Top of Pot.
VOUT = 0V, Slider at Center of Pot.
VOUT = –10V, Slider at Bottom of Pot.
10kΩ
Linear
5
R1
25kΩ
3
R3
25kΩ
R2
25kΩ
6
VOUT =
+10V to –10V
1
R4
25kΩ
FIGURE 2. –10V to +10V Adjustable Precision Voltage Source.

1990 Burr-Brown Corporation
AB-006
Printed in U.S.A. April, 1990
resulting voltage drop adds to the required swing at the
output of the op amp. Keep the voltage drop across R 3 low
—less than 1V at full load—to prevent the amplifier output
from swinging too close to its power-supply rail.
In many instances adjustable voltage sources need the ability
to drive high-capacitance loads such as power-supply bypass
capacitors. The additional circuitry needed to drive high
capacitance is shown in Figure 3. For stability, keep C LOAD•R3
needed, the unity-gain inverting amplifier is made with an
op amp and discrete resistors. For precision, R 1 and R2 must
be accurately matched. Also, load current flows in R 3. The
For applications with substantial volume (e.g. 5k ea/year) a
version of the INA105 with the op amp inverting input
brought out is available as a special (2A660). Inquire with
+VS
2
V+
REF102
10V 6
Out +10V
R1
10kΩ
R2
10kΩ
C2
Gnd
0.01µF
4
VOUT = +10V, Slider at Top of Pot.
VOUT = 0V, Slider at Center of Pot.
VOUT = –10V, Slider at Bottom of Pot.
OPA27
10kΩ
Linear
R3
50Ω
VOUT =
+10V to –10V