
OP196/OP296/OP496
REV. A
–13–
bypass capacitor at the false-ground output. T he benefit of a
large capacitor is that not only does the false-ground present a
very low dc resistance to the load, but its ac impedance is low as
well.
+5V OR +12V
6
2
3
10k
OP196
100
4
0.022μF
1μF
240k
240k
1μF
+2.5V OR +6V
7
Figure 41. A Micropower False-Ground Generator
Single-Supply Half-Wave and Full-Wave Rectifiers
An OP296, configured as a voltage follower operating from a
single supply, can be used as a simple half-wave rectifier in low
frequency (<400 Hz) applications. A full-wave rectifier can be
configured with a pair of OP296s as illustrated in Figure 42.
A1
8
1
3
4
+5V
1/2
OP296
2k
2
A2
5
6
+2Vp-p
<
500Hz
7
1/2
OP296
R1
100k
R2
100k
V
A
FULL-WAVE
RECTIFIED
OUTPUT
V
B
HALF-WAVE
RECTIFIED
OUTPUT
10
0%
100
90
500mV
1V
500μs
500mV
f = 500Hz
INPUT
V
OUT
B
(HALF-WAVE
OUTPUT)
V
OUT
A
(FULL-WAVE
OUTPUT)
Figure 42. Single-Supply Half-Wave and Full-Wave
Rectifiers Using an OP296
T he circuit works as follows: When the input signal is above
0 V, the output of amplifier A1 follows the input signal. Since
the noninverting input of amplifier A2 is connected to A1’s out-
put, op amp loop control forces A2’s inverting input to the same
potential. T he result is that both terminals of R1 are at the same
potential and no current flows in R1. Since there is no current
flow in R1, the same condition must exist in R2; thus, the out-
put of the circuit tracks the input signal. When the input signal
is below 0 V, the output voltage of A1 is forced to 0 V. T his
condition now forces A2 to operate as an inverting voltage fol-
lower because the noninverting terminal of A2 is also at 0 V.
T he output voltage of V
OUT
A is then a full-wave rectified
version of the input signal. A resistor in series with A1’s
noninverting input protects the ESD diodes when the input
signal goes below ground.
Square Wave Oscillator
T he oscillator circuit in Figure 43 demonstrates how a rail-to-
rail output swing can reduce the effects of power supply varia-
tions on the oscillator’s frequency. T his feature is especially
valuable in battery powered applications, where voltage regula-
tion may not be available. T he output frequency remains stable
as the supply voltage changes because the RC charging current,
which is derived from the rail-to-rail output, is proportional to
the supply voltage. Since the Schmitt trigger threshold level is
also proportional to supply voltage, the frequency remains rela-
tively independent of supply voltage. For a supply voltage
change from 9 V to 5 V, the output frequency only changes
about 4 Hz. T he slew rate of the amplifier limits the oscillation
frequency to a maximum of about 200 Hz at a supply voltage
of +5 V.
59k
1/2
OP296/
OP496
100k
100k
FREQ OUT
f
OSC
= RC
<
200Hz @ V+ = +5V
1
C
V+
R
2
3
4
8
1
Figure 43. Square Wave Oscillator Has Stable Frequency
Regardless of Supply Voltage Changes
A 3 V Low Dropout, Linear Voltage Regulator
Figure 44 shows a simple +3 V voltage regulator design. T he
regulator can deliver 50 mA load current while allowing a 0.2 V
dropout voltage. T he OP296’s rail-to-rail output swing easily
drives the MJE350 pass transistor without requiring special
drive circuitry. With no load, its output can swing to less than
the pass transistor’s base-emitter voltage, turning the device
nearly off. At full load, and at low emitter-collector voltages, the
transistor beta tends to decrease. T he additional base current is
easily handled by the OP296 output.
T he AD589 provides a 1.235 V reference voltage for the regula-
tor. T he OP296, operating with a noninverting gain of 2.43,
drives the base of the MJE350 to produce an output voltage of
3.0 V. Since the MJE350 operates in an inverting (common-
emitter) mode, the output feedback is applied to the OP296’s
noninverting input.
1/2
OP296
4
1
3
2
8
1000pF
44.2k
1%
30.9k
1%
AD589
43k
1.235V
MJE 350
100μF
V
IN
5V TO 3.2V
I
L
<
50mA
V
O
Figure 44. 3 V Low Dropout Voltage Regulator