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Matlab Simulink Modelling of a Single-Phase Voltage Controlled Voltage Source Inverter
Matlab Simulink Modelling of a Single-Phase Voltage Controlled Voltage Source Inverter

APPLICATION OF BJT AS A BIDIRECTIONAL SWITCH FOR LOW VOLTAGE CIRCUIT PROTECTION

INTRODUCTION:
Circuit breakers protect electrical circuitry from damage due to an over current condition, such as a relatively high level short circuit or fault condition. Circuit breakers act as protecting switches capable of connecting and allowing currents to flow through loads under normal circuit conditions and disconnecting the load under specified abnormal conditions such as a short circuit.
Electronic Circuit Breakers generally use electromechanical switches. The conventional circuit breaker is connected in series with the supply so the response time of the circuit breakers is a very important performance parameter.Since this switch has to work with AC rather than DC the conduction characteristics of the switch must be the same in both the directions.
The circuit breaker designed with Solid state technology has free from arcing and switch bounce.Many types of power devices like IGBTs, BJTs and MOSFETs are available with different specifications. Most of the electronic circuit breakers are designed with IGBTs for fast acting and low losses. However, the IGBT still requires large drive current. But the choice of technology for a power switch is not always clear cut. Whilst MOSFETs have become the default choice for many designers, bipolar transistors have many useful attributes which can be used beneficially in certain applications.
The MOSFET and BJT is certainly the device of choice for device breakdown voltages below 250V. However, choosing between BJTs and MOSFET s is very application-specific and cost, size, speed and thermal requirements should all be considered. BJTs are very much suitable for low voltage applications.
BJTs are very much suitable for low voltage applications. This circuit results a fast turn off time in the range of few micro seconds as opposed to milliseconds for a mechanical circuit breaker. The present work progresses an all electronic circuit breaker based on BJTs especially suited for low voltage application switch.

WORKING OF CIRCUIT BREAKER:
An all electronic Circuit Breaker has been designed to connect a load and an ac voltage supply. This circuit basically requires a bidirectional switch that allows ac voltage, a sense resistor and a decision making circuit connected in series with the load. The bidirectional switch is needed to connect the source to the load both for the positive and negative half cycles of the input voltage under normal conditions. The bidirectional switching is performed by two BJTs.
When the circuit works normally the BJT is in saturation mode and so the load is connected with the source. Under any faulty condition the output of the decision making circuit goes low then base voltage drives the BJT to cutoff region. Therefore the load has to be now disconnected from the source. The output of the comparator is connected back to the base of the two transistors.

apps. on C

C interview questions
1.What will print out?
main()
{
char *p1=“name”;
char *p2;
p2=(char*)malloc(20);
memset (p2, 0, 20);
while(*p2++ = *p1++);
printf(“%s\n”,p2);
}
Answer:empty string.
2.What will be printed as the result of the operation below:
main()
{
int x=20,y=35;
x=y++ + x++;
y= ++y + ++x;
printf(“%d%d\n”,x,y);
}
Answer : 5794
3.What will be printed as the result of the operation below:
main()
{
int x=5;
printf(“%d,%d,%d\n”,x,x< <2,x>>2);
}
Answer: 5,20,1
4.What will be printed as the result of the operation below:
#define swap(a,b) a=a+b;b=a-b;a=a-b;
void main()
{
int x=5, y=10;
swap (x,y);
printf(“%d %d\n”,x,y);
swap2(x,y);
printf(“%d %d\n”,x,y);
}
int swap2(int a, int b)
{
int temp;
temp=a;
t=a;
a=temp;
return 0;
}
Answer: 10, 5

5.What will be printed as the result of the operation below:
main()
{
char *ptr = ” Cisco Systems”;
*ptr++; printf(“%s\n”,ptr);
ptr++;
printf(“%s\n”,ptr);
}
Answer:Cisco Systems

6.What will be printed as the result of the operation below:
main()
{
char s1[]=“Cisco”;
char s2[]= “systems”;
printf(“%s”,s1);
}
Answer: Cisco
7.What will be printed as the result of the operation below:
main()
{
char *p1;
char *p2;
p1=(char *)malloc(25);
p2=(char *)malloc(25);
strcpy(p1,”Cisco”);
strcpy(p2,“systems”);
strcat(p1,p2);
printf(“%s”,p1);
}
Answer: Ciscosystems
8.The following variable is available in file1.c, who can access it?:
static int average;
Answer: all the functions in the file1.c can access the variable.
9.WHat will be the result of the following code?
#define TRUE 0 // some code
while(TRUE)
{ // some code
}
Answer: This will not go into the loop as TRUE is defined as 0.
10.what will be printed as the result of the operation below:
int x;
int modifyvalue()
{
return(x+=10);
}
int changevalue(int x)
{
return(x+=1);
}
void main()
{
int x=10;
x++;
changevalue(x);
x++;
modifyvalue();
printf("First output:%d\n",x);
x++;
changevalue(x);
printf("Second output:%d\n",x);
modifyvalue();
printf("Third output:%d\n",x);
}
Answer: 12 , 13 , 13
11.What will be printed as the result of the operation below:
main()
{
int x=10, y=15;
x = x++;
y = ++y;
printf(“%d %d\n”,x,y);
}
Answer: 11, 16
12.What will be printed as the result of the operation below:
main()
{
int a=0;
if(a==0)
printf(“Cisco Systems\n”);
printf(“Cisco Systems\n”);
}
Answer: Two lines with “Cisco Systems” will be printed.
13.Which of the following is illegal
(a)void v;
(b)void *v;
(c)void **v;
(d)all are legal
Answer: void v
14.What is the output ?
#define int INTEGER /*line1*/
#define INTEGER int /*line 2*/
main()
{
INTEGER p=10; /*line 5*/
printf("%d",p);
}
o/p?
(a)compiler error at line 1
(b)compiler error at line 2
(c)compiler error at line 5
(d)No error,prints 10
Answer: c
15.main()
{
int counter=1;
for(;;)
{
counter++;
if(counter>9)
break;
}
Answer: 9 times loop executes.