assngment electric circuit (ALARM)

    UNIVERSITI TEKNIKAL MALAYSIA MELAKA

FACULTY OF ELECTRICAL ENGINEERING

ASSIGNMENT

ELECTRIC CIRCUIT II

BEKU 2233

GROUP MEMBERS

SITI SYAHIRAH ABDUL MUTALIB                                B011010410

MURNIE SHAKILLA SHIDAN                                         B011010209

ERNIFARHA ABDUL RAHIM                                           B011010320

CHERISTINA ANAK LILY                                                B011010314

PREPARED FOR

DR. GAN CHIN KIM

SUBMISSION DATE

16^th December 2011

Abstract

The silicon-controlled switch as known as SCS is one of the family of four-layer pnpn device other than silicon-controlled rectifier, SCR, gate turn-off switch, GTO and many more. The purpose of this report done is to review the principle of operation of this silicon-controlled switch (SCS) in one of its application that is alarm circuit. Other than that, simulation using Microsim Psipce is done to prove that the operation of the circuit is same as theoretical acknowledgement. Basically, SCS is similar to the SCR in construction with the exception being the SCS has two gates. It can be turned off by either terminal.  Normally the SCR is available in power rating slower than SCR and has faster switching time than SCR. Either gate could fire the SCS and it is also can be turned on with negative pulse in anode gate. To turn it off, a positive pulse would be applied to anode gate or by applying positive pulse to cathode gate.This alarm circuit was built with the SCS taken as the main experimental component in its application. Others component that are used to build this circuit connection are voltage supply of 12 V, the resistive load, R, variable resistance, R, inductor load, L, diode, D and a switch to control the ON and OFF of the circuit. The RS in this circuit is represented as R3 which is represents a temperature, light or radiation resistor, that is an element whose resistance will decrease with the application of the three energy source listed. As the rate effect occurred that caused by stray capacitance levels between gates, the 100 kΩ resistor is included to overcome this problem. The results gained also proved the sufficient base current would turn the SCS on with the application of a high frequency transient.

Background

  An alarm gives a warning signal to let people know that something has happened.  The most common form of alarm is likely to see is a burglar alarm on a house or other building. If the building is broken into, the burglar alarm gives a warning sound.  A modern alarm is an electronic system that can have many other uses.  For example, it can also warn of fire or high voltage levels. There is a difference between an alarm and a sensor system. Alarms continue to indicate that something has happened even if the cause stops.  e.g. A burglar opens a door and sets off an alarm.  Even if he closes the door the alarm continues. An electronic system that can continue to indicate that something has happened after the event has finished is known as a latch.

       In this alarm circuit there is R3 represent a temperature-, light-, or radiation-sensitive resistor, that is, an element whose resistance will decrease with the application of any of the three energy sources list above. The cathode gate potential is the determined by the divider relationship established by R3 and the variable resistor. However, if R3 decreases, the potential of the junction will increase until the SCS is forward-biased, causing the SCS to turn on and energize the alarm relay.

       SCS is silicon-controlled switch as shown below. They are a four layer pnpn device. The higher the anode gate current, the lower is the required anode-to-cathode voltage to turn the device on.

The 100kΩ resistor is included to reduce the possibility of an accidental triggering of the device through a phenomenon known as the rate effect. It is caused by the stray capacitance levels between gates. A high frequency transient can establish sufficient base current to turn the SCS on accidentally. The device is on or off by pressing the switch button, which open the conduction path of the SCS and reduce the anode current zero.       

Figure 1: alarm circuit

Methodology

Component	Quantity
Voltage supply 12V	1
Resistive load, R	2
Variable resistance, R	1
Inductive load, L	1
Diode, D	1
Switch	1

Figure 1

In this assignment, we use MicroSim Pspice software to simulate the alarm circuit diagram. First, the components were placed as depicted in Figure 1 above. Then, the values of each component were set as the following below:

     R₁= 100k ohm.

     R₃ = 1k ohm

     R₅ = 2k ohm

     L₁ = 0.67H

After that, we were set voltage supply to 12V. Finally, we run the schematics.

Results

Figure 2

Based on the simulation, the results that we get are:

Table 2

Component	Voltage(V)	Current (A)
R1	0	0
R3	0	0
R5	12	259.87
L1	-2.859	259.87
D1	-2.859	0

Discussions

Based on the simulation that is done, silicon-controlled switch, SCS has been applied in the alarm circuit. R₃ represents a temperature-, light- or radiation-sensitive resistor, that is, an element whose resistance will decrease with the application of any of the three energy sources listed above. The cathode gate potential is determined by the divider relationship established by R_S and the variable resistor. Note that the gate potential is at approximately 0V if R₃ equals the value set by the variable resistor since both resistors will have 12V across them. However, if R₃ decreases, the potential of the junction will increase until SCS is forward-biased, causing the SCS to turn on and energize the alarm relay.

The 100kΩ resistor is included to reduce the possibility of an accidental triggering of the device through a phenomenon known as the rate effect. It is caused by the stray capacitance levels between gates. A high-frequency transient can establish sufficient base current to turn the SCS on accidentally. The device is on or off by pressing the switch button, which opens the conduction path of the SCS and reduce the anode current to zero.

Conclusion

The silicon-controlled switch, SCS has the same characteristics as those for the silicon-controlled rectifier, SCR. As in theoretical applied in this simulation, when t is less than zero (initial condition), the switch is closed or in ON mode and there is current flow through the inductor which is could be gained from the waveform of circuit simulation. Nonetheless, when t is equal to zero, the switch will be opened (OFF) and current will not pass through the inductor.

Low impedance characteristic occurred between the collector and emitter when there is a pulse applied to the circuit. The branch diverts anode current from the SCS and dropped it below the held value and turned it off. However, this turn-off characteristic is possible if the correct value of R_S (R3) is employed.

The rate effect that caused by the stray capacitance levels between gates could be reduced by installed the 100 kΩ resistor. This simulation also proved that value of R_S (R3) would affect the potential junction of this circuit.