Construction Of Automatic Phase Changer

LOGIC CIRCULT
The logic circuit is built around a D type flip flop it is the flip flop that tells the system when to switch to generator or public supply. The operation of the system is described in the truth table bellow the logic control circuit operates in its set and reset mode. When the rising edge of the unstable clock the flip flop the flip flop shifts data from the data cd input to the output to off the generator and connect public supply to output when the voltage drops the comparator sends a low to the flip flop input which switches the generator on and change over the output to generator

X… don’t care Q and Q … outputs D …data input
TRANSISTOR SWITCHING CIRCUIT
The switching transistor switches the relay which selects between the switch generators and the public supply.
The transistor as a switch operates in class a mode as described by the raja (2002). The relay is switched on when the flip-flop is in set mode as on when the flip flop is in set mode base resistor is required to ensure perfect switching of the transistor from back emf that might be generated since the relay coil present an inductive load. In this case rc which is the collector resistance is the resistance of the relay coil which is 400-2 for the relay type used in this project hence given that rc=400-2(relay coil resistance)
V+=12v (regulated voltage from the power supply stag) VBB = 0.6V (silicon)
VCB = OV (when transistor is switched)
VIN =5V (c from the flip flop stage)
HFE =300(from data sheet for BC 337)
Since
VT =ICRC+VCB - - - - - - - - - - - - (8)
VIN =IBRB +BB - - - - - - - -- - - - - (9)
HFE =IC/IB - - - - - - - - - - - - -- - (10)

RB =VIN –VBB - - - - - - - - - - - - (11)
          IB
Where IC collector current
BI =base current
VIN =input voltage
V+ =supply voltage
VCC =collector emitter voltage
HFE =current gain
From equation 8, IC =30ma
From equation 10, IB = 100 UA
From equation 9, RB =44k2
    = 47k -2(preferred value)
Where
Vunreg = unregulated d.c voltage
VR2(d.c) = drop across
Relay switching circuit
    A relay is an electromagnetic device that is used by varying the input in order to get a desired output. Relays are of two types, the normally closed and normally open c from texas instruments, data sheets,Anon 2003 -2007. The type used in this project is the normally open relay.
     It is good and common practice to switch a relay with transistor is set in the common emitter configuration.