Half‐wave rectifier with capacitive filter
Breadboard
Elettronica II
Prof. Paolo Colantonio
2 | 9
Source
Elettronica II
Prof. Paolo Colantonio
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Oscilloscope
Elettronica II
Prof. Paolo Colantonio
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• Let us consider a half‐wave rectifier with a capacitive load, used to produce a
steadier output
t1 < t < t2
D
When vi > VON, the diode is ON and the current flows toward R and C. C is charging with a low
RL
v(t)
i
C
v o  vi  VON
vo(t)
t2 < t < t3
The diode turns OFF and the capacitance discharge with law
t
VM
vo  Vm  VON   e

RC
vo
t
t1
Elettronica II
Prof. Paolo Colantonio
t2
t3
5 | 9
Assuming an high time constant RC>>T (period), then the exponential behaviour can be approximated with the tangent
VP
V
vp
t
t3
t2
In the time interval t2‐t3, we can write
vB  t
*
 V
P
e

t*
RC

t* 
 VP  1 

 RC 
Assuming t2‐t3 T, we can write
T  VP  T

V  V p  VP  1 

RC
RC


From which
RIPPLE 
Elettronica II
Prof. Paolo Colantonio
V
T

VP
RC
6 | 9
iD
A
t1 < t < t2  Diode ON
B
D
R
iR
C
iD  t   iC  t   iR  t   C
dvB  t 
dt

vB  t 
R
iC
t2 < t < t3  Diode OFF
vA
iD
vB
t
t1
t2
t3
The maximum current occurs at the circuit start up, when the capacitor C is discharged.
I D , MAX  C
Elettronica II
Prof. Paolo Colantonio
dvB  t 
dt
C
t 0
d
V p  sin t    2 f  C  V p
dt
t 0
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iD
vA
VP
vB
V
t
Dimensioning of RC to control the Ripple
V 
VP  T
RC
RIPPLE 
T
RC
Dimensioning of C to reduce the maximum current in the diode
I D , MAX  2 f  C  V p
Elettronica II
Prof. Paolo Colantonio
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Setup
Mount the circuit and apply a voltage signal Vpp=10V and f = 1kHz
A
D1N4001
B
Datasheet
Diode
1N4001
R
C
Conducting voltage
V=0.65V
Max current
Imax=30A
Work
• Determine the values for R and C in order to assure in B a Ripple < 10% of maxximum output voltage
Elettronica II
Prof. Paolo Colantonio
9 | 9