Circuits ELEC1250DiodesandDiode Lecture4
Examples of Diode Circuits: Rectifier Circuits
DCPowerSupply.
N1 Mains v m N2 v s Diode Rectifier Filter Voltage Regulator v o Load
HalfWaveRectifier
vd mains vi vo RL
rs
vd
vs
vi
vo
RL
EquivalentCircuitusingtheConstant VoltagedropandResistanceModel
rs
ideal
V DO
rd
vs
vi
vo
RL
PeakInverseVoltage(PIV)
Two important design parameters:
q q
Maximum diode current. Peak Inverse Voltage (PIV).
PIV = Vs (peak)
The PIV is the largest reverse bias voltage the diode will experience in the circuit without breaking down.
Halfwaverectifier: onlyhalf(max!)waveformused
200.00m
i d
I
0v
-100.00m 2.00
V +V DO b
v s
Axis label
0v
-2.00 0.00 10.00m 20.00m Time [s] 30.00m 40.00m
FullWaveRectifier: bothhalfcyclesused
Two types:
D1 vi vo RL
D4 D1 vo RL D2 D3
Mains
-v
vi
+
i
D2
FullWaveRectifier
D1
+ +
Mains
-
+ v _ i
vi
vo
RL
D2
OperationofFullWaveRectifier
v Positive i
D1
+
Mains
+
vi vi vo RL
-
D2 D1
v Negative i
-
vi vi vo RL
Mains
+
D2
OperationofFullWaveRectifier
v Positive i
D1
+
Mains
+
vi vi
ON
vo RL
-
D2 D1
OFF
v Negative i
-
vi vi
OFF
vo RL
Mains
+
D2
ON
OperationofFullWaveRectifier
v Positive i
D1
+
Mains
+
vi vi
ON
vo RL
-
D2 D1
OFF
v Negative i
-
vi vi
OFF
vo RL
Mains
+
D2
ON
OperationofFullWaveRectifier
v Positive i
D1
+
Mains
+
vi vi
ON
vo RL
-
D2
OFF
What is PIV (peak inverse voltage) here? For bottom diode, will occur when sine wave is max positive at top
SteadyStateWaveforms
V i
2.00
~V DO
1.00
Output voltage [V]
0.00
-1.00
v
L
10.00m 20.00m Time [s] 30.00m 40.00m
-2.00 0.00
Assuming a constant-voltage-drop model for the diodes.
TheBridgeRectifier.
D4 D1 vo RL D2 D3
vi
-
+
OperationinPositivehalfcycle
D4
D1
+
vi
-
OFF v o ON
D2 RL
ON
+
-
OFF
D3
PIVforbridgerectifier
D4 D1 vo RL
Assuming constant voltage drop model
RL V DO vo
+
vi
-
+
D2
D3
vD 3 (reverse) = vo + vDO
D2
D3
Thus PIV = vi ( peak ) 2VDO + VDO = vi ( peak ) VDO
OperationinNegativeHalfCycle
D4 vo D1 RL
vi
ON
-
OFF
+
+
OFF
D2
ON
D3
Centretappedtransformervsbridge rectifier
What are the relative (dis)advantages of each? CT transfo: more complicated transformer diodes need higher PIV Bridge: 4 diodes instead of 2 Which is better? Are there sustainability / moral issues?
Transformers
Core made of steel q need for metal resources q recyclable but do we do so? Wire made of copper q often mined in poorer countries q working conditions often bad q but does earn income & foreign currency q recyclable as above
SteadyStateWaveforms
2.00
V i 2V DO
1.00 Output voltage [V]
0.00
-1.00
Vo
-2.00 0.00 10.00m 20.00m Time [s] 30.00m 40.00m
DCPowerSupply:Filter
DC Power Supply
v
s
Diode Rectifier
Filter
Voltage Regulator
v
o
Load
FilterCircuit
Filter Capacitor vi C v o R L
CR >> T
VoltageWaveformsforfullwaverectifier
vi
2.00
V p
Output
1.00
Output Ripple V r
0.00
-1.00
vo
-2.00 0.00 10.00m 20.00m Time [s] 30.00m 40.00m
T
CapacitanceFilter
At the end of the discharge period Vo Vr Vo e T / 2 CR Since CR >> T then T T / 2 CR e 1 2CR Giving Vo T Vr Vo = 2CR 2 fCR 1 where f is the frequency = T
Example
Consider a fullwave rectifier fed by a 50...