The document discusses the operation of SCR (Silicon Controlled Rectifier) phase control circuits, focusing on half-wave and full-wave configurations. It outlines how the gate current and phase angles impact the average power delivered to the load during conduction periods. Additionally, it describes the differences between unidirectional and bi-directional full-wave control circuits, highlighting their individual functionalities and characteristics.

1. Industrial Electronics
p2-1
SCR Phase Control
Circuit
- Half-wave Circuit
- Full-wave Circuit)

2. Industrial Electronics
SCR : HALF-WAVE PHASE CONTROL
CIRCUIT
p2-2
Trigger
Circuit
SCR1
AC
supply Load
• SCR conducts only when :
- Anode - Cathode is Forward bias
- Trigger Circuit applies Gate current
• Conducts during the positive half cycle
• Average power to Load is controlled by :
- Gate current (firing delay angle)
- Phase angle of conduction period
• Power refers to Heat, Speed, Light &
Sound

3. Industrial Electronics
SCR : HALF-WAVE PHASE CONTROL WAVEFORMS
p2-3
t
VAK
t
t
Vload
d1 d2
d5 d5
VAK
Vload
d6 d4
d3
d6
t
d1, d2, d3, d4 - Firing Delay Angle
d5, d6 - Conducting Angle
Firing Delay Angle :
d1=800
, d2=2600
, d3,=1600
, d4=3300
Average Power :
• Larger phase angle conduction period = higher average power
• Small phase angle conduction period = lower average power

4. Industrial Electronics
SCR : FULL-WAVE PHASE
CONTROL CIRCUIT
p2-4
2 types of Full-wave control
circuits :
• Unidirectional
• Bi-directional

5. Industrial Electronics
UNI-DIRECTIONAL FULL-WAVE PHASE CONTROL CIRCUIT
p2-5
Trigger
Circuit(s)
SCR1
SCR2
AC
supply
Load
VLoad
t
VLoad
t
• Circuit function like normal full-wave rectifier
• SCR1 & SCR2 conducts only when :
- Anode - Cathode is on Forward bias (+ve cycles)
- Trigger Circuit applies Gate current
• DC pulsating voltage is produced at Load
• Phase angle of triggering can be controlled (delay)
• Load power needs determines trigger delay angles
• Larger phase angle conduction period = higher average power
• Small phase angle conduction period = lower average power

6. Industrial Electronics
BI-DIRECTIONAL FULL-WAVE PHASE CONTROL CIRCUIT
p2-6
Trigger
Circuit(s)
SCR1
SCR2
AC
supply
VLoad
t
• Large firing delay; small conduction
• Small power delivered to Load
• Firing angle = 1350
• Conduction angle = 450
• 2 SCR connected in opposite direction
• SCR receives positive voltage in each half cycle
• SCR1 & SCR2 conducts alternately when :
- Anode - Cathode is on Forward bias (+ve cycles)
• Trigger current is applied at the same time
• Unrectified voltage is produced at Load (as in waveform above)
• Phase angle of triggering can be controlled (delay)
• Load power needs determines trigger delay angles
• Larger phase angle conduction period = higher average power
• Small phase angle conduction period = lower average power

7. Industrial Electronics
BI-DIRECTIONAL FULL-WAVE PHASE CONTROL CIRCUIT
p2-6
Trigger
Circuit(s)
SCR1
SCR2
AC
supply
VLoad
t
• Large firing delay; small conduction
• Small power delivered to Load
• Firing angle = 1350
• Conduction angle = 450
• 2 SCR connected in opposite direction
• SCR receives positive voltage in each half cycle
• SCR1 & SCR2 conducts alternately when :
- Anode - Cathode is on Forward bias (+ve cycles)
• Trigger current is applied at the same time
• Unrectified voltage is produced at Load (as in waveform above)
• Phase angle of triggering can be controlled (delay)
• Load power needs determines trigger delay angles
• Larger phase angle conduction period = higher average power
• Small phase angle conduction period = lower average power