SCS and GTO
EE 133
Thyristor
Shockley Diode
Silicon-Controlled Rectifier (SCR)
Light-Activated SCR (LASCR)
Silicon-Controlled Switch (SCS)
Gate Turn-Off Switch (GTO)
Diac & Triac
Silicon-Controlled Switch (SCS)
The silicon-controlled switch (SCS) is a four-layer pnpn device, like SCR, but with an addition of
another gate.
Silicon-Controlled Switch (SCS)
The SCS can be triggered on or tuned off by an appropriate signal at either gate.
Silicon-Controlled Switch (SCS)
The SCS is a low power device compared with the SCR. It handles currents in milli-amperes
rather than amperes.
Since only small currents are involved, the SCS may be switched off by an appropriate polarity
pulse at one of the gates
Silicon-Controlled Switch (SCS)
In general, the triggering (turn-on) anode gate current is larger in magnitude than the required
cathode gate current.
For one representative SCS device, the triggering anode gate current is 1.5 mA, whereas the
required cathode gate current is 1 mA.
Silicon-Controlled Switch (SCS)
An advantage of SCS over an SCR is the reduced turn-off time, typically within the range of 1 to
10 micro seconds for the SCS and 5 to 30 micro seconds for the SCR. Other advantages of the
SCS over SCR are increased control and triggering sensitivity
More predictable firing situation (FOR RECTIFIERS ONLY)
DISADVANTAGE:
Limited to low power, current and voltage rating
Silicon-Controlled Switch (SCS)
Silicon Controlled Switch (SCS) is used in pulse generators, voltage sensors, counters, timing,
logic and triggering circuits.
The device is used in lamp drivers, power-switching circuits, and logic circuits as well as in
essentially any circuit that requires a switch that can be turned ON and OFF by two separate
control pulses.
Thyristor
Shockley Diode
Silicon-Controlled Rectifier (SCR)
Light-Activated SCR (LASCR)
Silicon-Controlled Switch (SCS)
Gate Turn-Off Switch (GTO)
Diac & Triac
Gate turn-off switch (GTO)
Gate turn-off switch (GTO) is, like an SCR, is a four layer, three junction semiconductor device
with three external terminals, namely, the anode, the cathode and the gate.
Gate turn-off switch (GTO)
Although the graphical symbol is different from that of either the SCR, the transistor equivalent
is exactly the same and the characteristics are similar.
The most obvious advantage of the GTO over the SCR or SCS is the fact that it can be turned on
or off by applying the proper pulse to the cathode gate
The device is turned on by a positive gate current and it is turned off by a negative gate cathode
voltage.
Gate turn-off switch (GTO)
Gate turn-off switch (GTO)
The turn-off current of a GTO is slightly larger than the required triggering current.
The maximum rms current and dissipation ratings of GTOs manufactured today are limited to
about 3 A and 20 W, respectively.
The majority of the SCR turn-off circuits can also be used for GTOs.
Gate turn-off switch (GTO)
GTO has improved switching characteristics.
The turn-on time is similar to that of the SCR (typically 1 micro second), but the turn-off time of
about the same duration (1 micro second) is much smaller than the typical turn-off time of an
SCR (5 ms to 30 ms).
The fact that the turn-off time is similar to the turn-on time rather than considerably larger
permits the use of this device in high-speed applications.
Gate turn-off switch (GTO)
Applications include counters, multivibrators, pulse and sawtooth generators.