SWITCHABLE NON-INVERTING / INVERTING AMPLIFIER
Block diagram
This is a circuit I found in a book about op-amps some 25 years ago. When SW1 is open, the amplifier
operates in a non-inverting mode, and the output signal follows the input exactly. When SW1 is closed,
the amplifier operates in an inverting mode and the output is inverted.
Input
R2
10K
Output
Invert
XSG1
8V / 1Hz
XSC1
12V
R3
10K
Ch.1
Ch.2
Sig In
Sig Out
0V
0V
R4
4.7K
IC1
LM741
R1
4.7K
-12V
Sig In
Sig In Sig Out
Invert
SW1
0V
A more practical approach is to use an NPN transistor as a switch.
A logic signal or voltage above 0.7v will invert the amplifier.
R6
10K
Input / Output Signals
10
Voltage [V]
12V
R7
10K
5
Input
Output
0
R8
4.7K
R5
4.7K
IC2
LM741
-12V
-5
Invert
R9
10K
-10
0
1
2
3
4
Time [s]
5
6
7
8
Q1
0V
by Phil Townshend