power control devices
TRANSCRIPT
Revision 01 1
Power control devices
• Silicon Controlled Rectifier
• Triac
• Diac
• GTO
• BJT
• MOSFET
Can be turned off while anode current is still flowingCan be turned off while anode current is still flowing
Once they are triggered into conduction, they can only be stopped by turning off current external to the device.
Once they are triggered into conduction, they can only be stopped by turning off current external to the device.
ThyristorsThyristors
Revision 01 2
• SCRs can switch high currents from about 1A – 2000A
• SCRs turn ON when the +ve potential is applied to the gate terminal provided the anode is +ve with respect to the cathode.
• An SCR can only turn off if the anode current is reduced below its holding value with the gate open.
Power devices - SCRs
Revision 01 3
NE185 Power Control Systems
Silicon controlled rectifier (thyristor)
Small Currentto “trigger” SCR
Large CurrentLarge Current
Anode (A)
Cathode (K)
Gate (G)
Revision 01 4
Silicon controlled rectifier (thyristor)
Note: The process of turning an SCR ON is called TRIGGERINGThe process of turning an SCR OFF is called COMMUTATION
Small Currentto “trigger” SCR
Large Current
Anode (A)
Cathode (K)
Gate (G)
Small Currentto “trigger” SCR
Large CurrentLarge Current
Anode (A)
Cathode (K)
Gate (G)
Anode (A)
Cathode (K)
Gate (G)
Revision 01 5
Silicon controlled rectifier (thyristor)
Small Currentto “trigger” SCR
Large Current
Anode (A)
Cathode (K)
Gate (G)
Small Currentto “trigger” SCR
Large CurrentLarge Current
Anode (A)
Cathode (K)
Gate (G)
Anode (A)
Cathode (K)
Gate (G)
Note: The ONLY way to turn them off is to stop the current flowing.They must then be re-triggered on.
Revision 01 6
Silicon controlled rectifiers
Revision 01 7
Revision 01 8
Revision 01 9
Silicon controlled rectifier
Revision 01 10
Silicon controlled rectifier
Revision 01 11
Silicon controlled rectifier
Gate
Anode
Cathode
N
P
N
P
N
P
N
P
P
N
Cathode
Anode
Gate
4-layer device
Revision 01 12
Silicon controlled rectifier
Anode
Cathode
Gate
Q1
Q2
Load
Revision 01 13
SCR control: phase control
Silicon Controlled Rectifier (Thyristor)
Current required for triggering SCRCurrent required for triggering SCR
Load CurrentLoad Current
A N
Load
A NA N
Load
Revision 01 14
SCR control: phase control
Silicon Controlled Rectifier (Thyristor)
Current required for triggering SCRCurrent required for triggering SCR
Load CurrentLoad Current
Lower resistance on potentiometer. Capacitor
charges quicker
A N
Load
A NA N
Load
Revision 01 15
SCR control: phase control
Silicon Controlled Rectifier (Thyristor)
Current required for triggering SCRCurrent required for triggering SCR
Load Current
Higher resistance on potentiometer. Capacitor
charges slower
A N
Load
A NA N
Load
Revision 01 16
SCR controlSilicon Controlled Rectifier (Thyristor)
Control
Control
A N
Load
Control
Control
A N
Load
SCR’s only conduct in one direction. Above is one way top overcome this.
Revision 01 17
T1
T2
GATE
TRIAC
Revision 01 18
T2T1 GT2T1 G
SC151D
T2
T1GST4
500k
10k
120V
0.27µF
TRIAC Light Dimmer
Diac
Revision 01 19
Phase control
+V
-V
180° 270° 360°90°
SCR1 conducts
SCR2 conducts
SCR1 conducts
SCR2 conducts
Revision 01 20
Phase control
+V
-V
180° 270° 360°90°
SCR1 conducts
SCR2 conducts
SCR1 conducts
SCR2 conducts
Revision 01 21
Phase control
+V
-V
180° 270° 360°90°
SCR1 conducts
SCR2 conducts
SCR1 conducts
SCR2 conducts
The main disadvantage of Phase Control (indeed SCR control) is RFI.
Revision 01 22
-VA
IHOLDINGVBR(R)
IHOLDING VBR(F)
FORWARD
REVERSE
- IA
+IA
+VA
28-36V typical28-36V typical
Diac characteristic curves
Revision 01 23
Gate turn-off thyristers (GTO’S)
• A gate turn-off switch, also known as a gate-controlled switch (GCS) or gate turn-off thyristor (GTO), is similar to an SCR but can be turned off by a negative signal on the gate terminal.GTOs generally handle much lower currents than SCRs
Anode
Cathode
Gate
Anode
Cathode
Gate
Revision 01 24
Transistor• BJT Transistors • A transistor is a device which acts like a controlled valve. The
current flow permitted can be controlled. • The bipolar junction transistor (BJT) is a three-terminal
electronic valve - the output (collector) terminal current-voltage characteristics are controlled by the current injected into the input port (base). The BJT is a semiconductor device constructed from two pn junctions. There are two types of BJT: pnp and npn.
Revision 01 25
Transistor
• A transistor may be thought of as an electronic tap able to control a large flow of electrons with only small variations of the 'handle'. The 'handle' in the case of a transistor is called the "base". The in and out 'pipes' are called the "emitter" and the "collector".Voltage changes at the base of the transistor result in changes to the flow of electricity through the transistor.
• A transistor can be thought of as a 'tap'.• Symbol for a Transistor
Revision 01 26
Transistor operation
Emitter
Collector
Base
1. Bi-Junction Transistor (BJT)
Collector
Emitter
Base
NPN
PNP
P
PN
N
NP
Transistors are three layer devices
P
PN
P
PN
N
NP
Transistors are three layer devices
Revision 01 27
Transistor operation
Emitter
Collector
Base
1. Bi-Junction Transistor (BJT)
Collector
Emitter
Base
NPN
PNP
Small currentSmall current
Large currentLarge current
Large currentLarge current
Small currentSmall current
BJT’s are current operated devices
Revision 01 28
Transistor operation
2. MOSFET Transistor
Drain
Gate
Source Source
Drain
Gate
Source
Drain
Gate
Source
Drain
Gate
N-ChannelEnhancement
Mode only
P-ChannelEnhancement
Mode only
N-ChannelEnhancement
/Depletion Mode
P-ChannelEnhancement
/Depletion Mode
Drain
Gate
Source
Drain
Gate
Source
GateGate
Source Source
Drain
Gate
Source
Drain
Gate
Source
Drain
Gate
Source
Drain
Gate
Source
Drain
Gate
Source
Drain
Gate
N-ChannelEnhancement
Mode only
P-ChannelEnhancement
Mode only
N-ChannelEnhancement
/Depletion Mode
P-ChannelEnhancement
/Depletion Mode
Revision 01 29
Transistor operation
2. MOSFET Transistor
Drain
Gate
Source
Negative
Positive
Negative
Positive
A positive voltage (around +5V) on the
gate turns the transistor fully on
In other words, they are VOLTAGE DRIVEN DEVICES.
Remember?… BJT’s are CURRENT DRIVEN DEVICES.
RDS off = MΩ
RDS on = <0.1Ω
Revision 01 30
Transistor operation
• Advantages of transistors over thyristors:– Lower voltage drop across transistors when
conducting (0.1V as compared to 2V) This causes less heat to be developed.
– Faster switching times – (less time to turn on = less heat developed while
turning on)– Can easily be turned off.
Revision 01 31