Search This Blog

Powered by Blogger.


Home » » SCS-Silicon Controlled Switch

SCS-Silicon Controlled Switch

Silicon Controlled Switch
Silicon Controlled Switch
Silicon controlled switch (SCS), like the SCR, is a unilateral, four layer three junction P-N-P-N silicon device with four electrodes namely cathode C, cathode gate Gx, anode gate G2 and the anode A, as shown in figure. Infact, the SCS is a low power device compared with the SCR. It handles currents in milli amperes rather than amperes. SCS differs from an SCR in the following aspects. It has an additional gate—the anode gate.It is physically smaller than SCR.It has smaller leakage and holding currents than SCR.It needs small triggering signals. It gives more uniform triggering characteristics from sample to sample.
The basic structure and schematic symbol of SCS are shown in the figures. It may be fabricated by using either the grown junction technique or the planar technique.
SCS Symbol
SCS Symbol

Operation of a Silicon Controlled Switch

The easiest way to understand how it operates is to realize it to be formed of two transistors Q1 and Q2 placed back-to-back, as shown in figure.b
In a two-transistor equivalent circuit shown in figure.c, it is seen that a negative pulse at the anode gate G2 causes transistor Qto switch on. Transistor Q1 supplies base current to transistor Q2, and both transistors switch-on. Similarly, a positive pulse at the cath­ode gate G1 can switch the device on. Since only small currents are involved, the SCS may be switched off by an appropriate polarity pulse at one of the gates. At the cathode gate a negative pulse is required for switching-off while at the anode gate a positive pulse is needed.
Silicon Controlled Switch Characteristics
Silicon Controlled Switch Characteristics

Volt-Ampere Characteristic of SCS

The volt-ampere characteristic of an SCS is similar to that of an SCR and is shown in figure. With the increase in applied voltage, the current first increases slowly upto point A and then rapidly in the region AB, as shown in the figure. At point B, the product β1β2 exceeds unity and the device is suddenly switched on. In the on-state, the current increases enormously and is limited by the external series resistor. SCS also exhibits negative differential resistance in the on region similar to SCR. SCS gets switched on accidentally if the anode voltage gets applied suddenly. This is known as rate effect, which is caused by inter-electrode capacitance between elec­trodes G1 and G2, known as transition capacitance.
Advantages and Applications of 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 and a more predictable firing situation. However, the SCS is limited to low power, current, and voltage ratings (typical maximum anode currents range from 100 mA to 300 mA with dissipation rating of 100 to 500 mW).
A few of the more common areas of application of SCS include a variety of computer circuits (such as counters, registers, and timing circuits) voltage sensors, pulse generators, oscillators etc

Share this on your favourite network


Post a Comment

Write For Us

Submit a Guest Post

Find us on Facebook


555 Timer IC 7 segment Display 8051 Project AC Circuits Adafruit Alarms Amplifier Circuits Analog Circuits android Arduino arm processor Assembly Languange Atmel Atom Size Audio Circuits augmented reality Automotive Circuits avr Battery Circuits Bicycle Gurad bluetooth Cable TV Circuits Cambridge University Camera Technology Circuit Boards Clipping And Clamping Circuits Clocking And Timer Circuits Computing contact lens Contact Us Form Contests Controller Circuit Conversion Circuits Counter Circuits Digital Electronics diy circuits Downloads EFY EFYTimes Electronic Books Electronic Components Electronic Locks And Keys Engineering Fan Circuits Filter Circuits Fire Alarm free Frequency Fun And Game Circuits future Google Hack n Mod Ham Radio Circuits heart rate monitoring High Voltage Circuits Home Circuits IC Guide ieee Industrial Circuits Infrared Instructables Inventions ipad lcd Led Circuits Light Related Lighting Circuits Medical Circuits Meter Clocks Microcontrollers Microprocessors Mini Projects modules Movie maker NatGeo Navigation Notice Optical Fiber PC Circuits PCB Boards Physics pnp transistor Power Supplies Printing Projects Programmer Project Ideas Projectors Protection circuits Proximity Detectors Radar Radio Circuits Radio Transmitters Raspberry Raspberry Pie Remote Circuits Retis Lab RFID Robot Cars Robotics Science Science Alert Security And Safety Sensor Circuits Servo Motors Smallest Smartwatches sms Software solar cell sound application Spectram Switch Technology News Telephone Related Television Related Test And Measurement Circuits Thermal Projects Tone generator circuits Touch Screen Tutorials Wearables Wi-Fi Wireless
Like us on Facebook
Follow us on Twitter
Recommend us on Google Plus
Subscribe me on RSS