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Various types of rectifier circuits using operational amplifiers (op-amps) and diodes. Topics include ideal diodes, faster rectifiers, two-stage rectifiers, active full-wave rectifiers, and peak detectors. Each circuit is explained with its corresponding waveforms and operating conditions.
Typology: Exams
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Op amps can be used with diodes to create better properties.
-^
Real diodes have a forward “diode drop” and small reverse current.
B
I^
I^ S
e
VΔ (^)
V^ ⁄ T
1
(^
)
=
V^ D
V ≅
V
Forward
vout
V 0
Reverse
vin
R 0 L
The simple rectifier uses a diode to short signals
-^
This cannot rectify signals less than 0.6 V.
-^
Feedback can be used to make an “ideal” diode.
-^
If
v
in
v
out
v
v
v
in
,^ v
a^
v
in
If
v
in
v
a^
< 0, the diode is non-conducting and
v
out
This circuit is slew rate limited, for negative signals it goes to -
EE
v^ out
v^ in
v^ out
10 k
Ω
v^ in
v^ a
Add a x1 inverter before this circuit to make a conventional rectifier that passes positive signalsonly. The first amplifier stage provides a -1 inverter with 100 k
input impedance.
The second amplifier acts as a half wave rectifier.
v^ out
− +
10 k
Ω
v^ in
v^ a
10 k
Ω D
2
D
1
100 k^ − +
Ω
100 k
Ω
Two amplifiers can be used to make a full-wave rectifier.
-^
A switchable inverter/buffer can use an op-amp as the switch.
-^
If v
in
< 0, v
cont
= 0.6, and the circuit inverts.
If v
in
> 0, the diode is non-conducting, so no feedback.
vin
v^ out
10 k − +
Ω
10 k
Ω
v^ cont
is low for follower
v^ cont
is high for inverter
10 k
Ω v^ cont − +
A diode and a capacitor can be used as a peak detector.
-^
The voltage through the diode is stored on the capacitor.
-^
The voltage is stored as a charge
until a higher value comes along.
The diode drop matters;
v
in
vin
vout
i^ D i^ C
i^ C
C
v^ dout
= If v
out
> v
in
− 0.6 V, i
C^
= 0, v
out
= const.
If v
out
< v
in
− 0.6 V, v
out
= v
in
An active rectifier can be combined with a capacitor to store the true input voltage.
-^
The first amplifier is set up as an ideal diode.
-^
Positive voltage through the diode is stored at the capacitor. The response is limited by the slewrate and output current,
max
, of the first amplifier.
The second amplifier is a x1 buffer and the large input impedance (related to
) prevents theB
capacitor from draining too rapidly.
v^ in
v^ out
− +
μ
F
− +
dv^ out^ td
max
(^1) ----^ C dQtd
I^ max C
=^
=
dv^ out^ td
droop
