ELECTROPHORESIS MACHINE 6

switch control circuits and large starter motors, electric heaters, pilot lights and available signal devices. Basically, they are used in remote switching and high voltage or current switch
2.1 ANALYSIS OF COMPONENTS/UNITS
2.1.1 POWER SUPPLY UNIT
Almost all the electronic circuit from simple transistor and operational amplifier circuit up to digital and microprocessor systems requires one source of stable voltage.

A regulated power supply can be constructed by using negative feedback to compare the dc output voltage with a stable reference voltage. The block diagram of such a power supply is shown below in fig. 2.11.
Output
REGULATOR
FILTER
RECTIFIER
TWO-WINDING TRANSFFORMER
Mains
Source
INPUT

Fig. 2.11
The transformer normally, changes the mains supply voltage to a value which is safe to work with and some what more than the wanted dc voltage but which is not more than that the regulator can handle. But because a voltage of not less than 200v is needed for this project, a two-winding transformer which is same as auto-transformer in function is adopted for the transformer stage.

The transformer output is rectified using a bridge rectifier producing fluctuating d.c voltage which is then passed through a filter capacitor. The filter is required to remove the ripple voltage of frequency equal to twice mains frequency for bridge rectification. The filter is basically a shunt electrolytic capacitor that charged up the peak value of the input voltage with a large discharge time to prevent it been completely discharged when the fluctuating d.c voltage is going low. Hence, there is always a voltage output across any load connected. The output voltage from the filter is then fed into a linear regulator whose rating is compatible to handle this voltage. (6)

2.1.2 THE RELAY UNIT
Relay, are electrically controlled switches. Relays allow a small current flow circuit to control a higher current circuit. Many varieties are available including latching and stepping relays. Several design of relay are in use today 3 pin, 4-pin, and 6-pin single switch or dual switches.

Magnetic relays are used as dev ing. A relay is made up of a coil which determines the on and off state of the device and operate based on the principle that when current increases in a coil the e.m.f due to self induction acts in opposite direction to it and consequently magnetizing or drawing in or close a switch. The decrease of current causes the opposite effect.



Fig. 2.12