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P a g e
Figure above shows the single phase half wave rectifier with RL Load.
Normally motors are inductive loads
L= armature
of field coil inductance
R= Resistance of coil.
In positive half cycle, SCR starts conduction at firing angle “α”.
Drop across SCR is small & neglected so output voltage is equal to supply voltage.
Due
to ‘R
L
’ load, current through SCR increases slowly.
At ‘π’, supply voltage is at zero where load current is at its max value.
In positive half cycle, inductor stores energy & that generates the voltage.
In
negative half cycle, the voltage developed across inductor, forward biases SCR & maintains its
conduction.
Basically with the property of inductance it opposes change in current.
Output current & supply current flows in same loop,
so all the time i
o
=i
s
.
After π the energy of inductor is given to mains & there is flow of ‘io’. The energy reduces as if gets
consumed by circuit so current also reduces.
At ‘β’ energy stored in inductance is finished, hence ‘i
o
’ becomes zero & ‘T1’ turns off.
‘i
o
’ becomes zero from ‘β’ to ‘2π+α’ hence
it is discontinuous condu
ction.
The average output voltage V
0
=
=
π
α
β
I
0
=
π
α
β
RMS load voltage V
0r
=
=
