thyristors cont
Post on 07-Jul-2018
230 Views
Preview:
TRANSCRIPT
-
8/18/2019 Thyristors Cont.
1/20
THYRISTORS
cont.)
-
8/18/2019 Thyristors Cont.
2/20
Outline:
I. Unijunction TransistorII. Programmable Unijunction
Transistor
III. Insulated Gate Bipolar TranIV. Gate Turn off Switches
-
8/18/2019 Thyristors Cont.
3/20
UNIJUNCTION TRANSISTO
a three-terminal device with a p – n
junction formed between an aluminum rodand 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 semiconductordiode . The higher the applied voltage across
the device, the higher is the emitter firing
potential
originally called a duo (double) base diode
due to the presence of two base contacts
-
8/18/2019 Thyristors Cont.
4/20
UNIJUNCTION TRANSISTO
the emitter leg is drawn at anangle to the vertical line
representing the slab of n-
type material
The arrowhead is pointing in
the direction of conventionalcurrent (hole) flow when the
device is in the forward-biased,
active, or conducting state
-
8/18/2019 Thyristors Cont.
5/20
UNIJUNCTION TRANSISTO
-
8/18/2019 Thyristors Cont.
6/20
UNIJUNCTION TRANSISTO
-
8/18/2019 Thyristors Cont.
7/20
UNIJUNCTION TRANSISTO
APPLICATION: SCR TRIGGERING
-
8/18/2019 Thyristors Cont.
8/20
UNIJUNCTION TRANSISTO
Determine the value of this
circuit that will ensure proper
turn-on and turn-off of the UJT.
The characteristic of the UJT
exhibits the following values: η= 0.5, VV = 1V, IV = 10mA, IP =
20μA, and VP = 14V.
-
8/18/2019 Thyristors Cont.
9/20
PROGRAMMABLE UNIJUNCTIO
TRANSISTOR
a four-layer pnpn device with a gate connecteddirectly to the sandwiched
the term programmable is applied because RBB, η,
and VP as defined for the UJT can be controlled
through the resistors RB1, RB2, and the supply voltage
VBB
-
8/18/2019 Thyristors Cont.
10/20
PROGRAMMABLE UNIJUNCTIO
TRANSISTOR
-
8/18/2019 Thyristors Cont.
11/20
PROGRAMMABLE UNIJUNC
TRANSISTOR APPLICATION: RELAXATION OSCILLATOR
-
8/18/2019 Thyristors Cont.
12/20
PROGRAMMABLE UNIJUNC
TRANSISTOR APPLICATION: RELAXATION OSCILLATOR
-
8/18/2019 Thyristors Cont.
13/20
INSULATED GATE BIPOLA
TRANSISTOR
a hybrid device of power MOSFET and BJT high input impedance and high switching speeds of a MOSFE
low saturation voltage of a bipolar transistor, and comb
together to produce another type of transistor switching dev
capable of handling large collector-emitter currents with vir
gate current drive
-
8/18/2019 Thyristors Cont.
14/20
INSULATED GATE BIPOLA
TRANSISTOR Power JT whose basecurrent is provided by
FET
IGBT combines the lowconduction loss of a BJTwith the high switchingspeed of a powerMOSFET an optimal
solid state switch existswhich is ideal for use inpower electronicsapplications An insulated gate bipolar transistor is simply turned “ON” or “O
and deactivating its Gate terminal. Applying a positive input vol
the Gate and the Emitter will keep the device in its “ON” state,
input gate signal zero or slightly negative will cause it to turn “O
same way as a bipolar transistor or eMOSFET. Another advantag
-
8/18/2019 Thyristors Cont.
15/20
INSULATED GATE BIPOLA
TRANSISTOR
requires a small voltage on the Gate to maintain conduction through the devi
unidirectional device, meaning it can only switch current in the “forward direc
from Collector to Emitter
resistance offered by the main conducting channel when current flows throug
its “ON” state is very much smaller in the IGBT
the current ratings are much higher when compared with an equivalent powe
-
8/18/2019 Thyristors Cont.
16/20
INSULATED GATE BIPOLA
TRANSISTOR
main advantages of using the Insulated Gate ipolar Transitypes of transistor devices are its high voltage capability, low
ease of drive, relatively fast switching speeds and combined
drive current makes it a good choice for moderate spee
applications such as in pulse-width modulated (PWM), variable
switch-mode power supplies or solar powered DC-AC inverter
converter applications operating in the hundreds of kilohertz ra
-
8/18/2019 Thyristors Cont.
17/20
INSULATED GATE BIPOLA
TRANSISTOR
Device
Characteristic
Power
ipolar
Power
MOSFET
Voltage Rating High
-
8/18/2019 Thyristors Cont.
18/20
GATE TURN-OFF SWITCH
most obvious advantage of the GTO over the SCR or SCS is thecan be turned on or off by applying the proper pulse to the cat(without the anode gate and associated circuitry required for th
-
8/18/2019 Thyristors Cont.
19/20
GATE TURN-OFF SWITCH
A consequence of this turn-off capability is an increase in the m
the required gate current for triggering. For an SCR and GTO ofmaximum rms current ratings, the gate-triggering current of a pSCR is 30 mA, whereas the triggering current of the GTO is 2turn-off current of a GTO is slightly larger than the required trigcurrent. The maximum rms current and dissipation ratings of GTmanufactured today are limited to about 3 A and 20 W
second very important characteristic of the GTO is improved swcharacteristics. The turn-on time is similar to that of the SCR (tybut the turn-off time of about the same duration (1 ms) is mucthan the typical turn-off time of an SCR (5 ms to 30 ms). The facturn-off time is similar to the turn-on time rather than consider
permits the use of this device in high-speed applications
-
8/18/2019 Thyristors Cont.
20/20
GATE TURN-OFF SWITCH
top related