Terms in Industrial Electronics

Terms
1. The silicon-controlled rectifier (SCR) is a rectifier whose state is controlled by the magnitude of the gate current. The forward-bias voltage across the device will determine the level of gate current required to “fire” (turn on) the device. The higher the level of biasing voltage, the less is the required gate current.
2. In addition to gate triggering, an SCR can be turned on with zero gate current simply by applying the sufficient voltage across the device. The higher the gate current, however, the less is the required biasing voltage to turn the SCR on.
3. The silicon-controlled switch has both an anode gate and a cathode gate for controlling the state of the device, although the anode gate is now connected to an n-type layer and the cathode gate to a p-type layer. The result is that a negative pulse at the anode gate will turn the device on, whereas a positive pulse will turn it off. The reverse is true for the cathode gate.
4. A gate turn-off switch (GTO) looks similar in construction to the SCR with only one gate connection, but the GTO has the added advantage of being able to turn the device off and on at the gate terminal. However, this added option of being able to turn the device off at the gate results in a much higher gate current to turn the device on.
5. The LASCR is a light-activated SCR whose state can be controlled by light falling on a semiconductor layer of the device or by triggering the gate terminal in a manner described for SCRs. The higher the junction temperature of the device, the less is the required incident light to turn the device on.
6. The Shockley diode has essentially the same characteristics as an SCR with zero gate current. It is turned on by simply increasing the forward-bias voltage across the device beyond the breakover level.
7. The diac is essentially a Shockley diode that can fire in either direction. The application of sufficient voltage of either polarity will turn the device on.
8. The triac is fundamentally a diac with a gate terminal to control the action of the device in either direction.
9. The unijunction transistor is a three-terminal device with a p-n junction formed between an aluminum rod and an n-type silicon slab. Once the emitter firing potential is reached, the emitter voltage will drop with an increase in emitter current, establishing a negative-resistance region excellent for oscillator applications. Once the valley point is reached, the characteristics of the device take on those of a semiconductor diode. The higher the applied voltage across the device, the higher is the emitter firing potential.
10. The phototransistor is a three-terminal device having characteristics very similar to those of a BJT with a base and collector current sensitive to the incident light intensity. The base current that results is essentially linearly related to the applied light with a level almost independent of the voltage across the device until breakdown results.
11. Opto-isolator contain an infrared LED and a photodetector to provide a linkage between systems that does not require a direct connection. The output detector current is less than but linearly related to the applied input LED current. Furthermore, the collector current is essentially independent of the collector-to-emitter voltage.
12. The PUT (programmable unijunction transistor) is, as the name implies, a device with the characteristics of a UJT but with the added capability of being able to control the firing potential. In general, the peak, valley, and minimum operating voltages of PUTs are less than those of UJTs.

13. Shottky Diode
Advantages:
1. Short Reverse Recovery Time
--- High speed rectifier
2. Low Voltage Drop in Forward Bias
--- High speed TTL IC 74S00 (ECL)
--- Low power TTL IC 74LS00 (TTL)
14. Tunnel Diode
Heavily doped, negative resistance
over forward bias range, so nice for
high frequency oscillator

15. Varicap Diode
PN junction cap decreases when
reverse biasing voltage increases
For variable cap to eliminate the
need of moving part 60pF/0v

16. Zener Diode
narrow junction, Zener breakdown, large change of current causes no
change of voltage, voltage regulator
• LED
III-V semiconductor, emitting photon when electron passes junction
17. Insulated Gate Bipolar Transistor (IGBT)
Combine the advantages
of MOSFET and BJT.
Gate structure like MOS
Output structure like BJT
High voltage 300-1700V

18. Diode AC Switch (DIAC)
Characteristic parameters:
1. Breakover voltage
2. Breakback voltage
3. Voltage symmetry
4. Rating current
5. Power dissipation

19. Triode AC Switch (TRIAC)
Advantages:
1. Controllable trigger
2. Four quadrant device
Application:
1. Light dimmer control
2. Motor speed control
Reason:
Trigger pulse can control
Any percentage of half cycle