Transformers

TRANSFORMER

A transformer is a device that transfers electrical energy between two or more circuits (primary and secondary) through mutual inductance. In voltage applied one circuit produces magnetic field into the other circuits.

As the name implies, transformer transforms voltage from one form to the other i.e from low voltage to high voltage, and vice versa. In power generating companies, electrical powers are generated at low voltages and then transform these voltages into a much higher voltage for transmission but these voltages cannot be consumed by our appliances. At the distribution level, this is then transformed into low voltages for our appliances to consumed. The reason for transforming the voltage to a much higher level is that higher distribution voltages implies lower currents for the same power and therefore lower I(square)R losses along the networked grid of cables.

In most electronic devices, transformers are mostly used to step down 230VAC to lower voltages such as 6,9,12,15,24,60, and 110volts etc. but in the case of inverter, the transformer is used in step up operation to step up low voltage from the oscillator into high voltage such as 230vav.

The two coils of the transformer are not electrically connected with each other but are instead wrapped together around a common closed magnetic iron circuit called the “core”. The two coil windings are electrically isolated from each other but are magnetically linked through the common core allowing electrical power to be transferred from one coil to the other. When an electric current passed through the primary winding, a magnetic field is developed which induces a voltage into the secondary winding

TRANSFORMER CONSTRUCTION

In the diagram above;

Vp - Primary Voltage

Vs - Secondary Voltage

Np - Primary Turns

Ns - Secondary Turns

Φ (phi) - Flux Linkage

When a transformer is used to “increase” the voltage on its secondary winding with respect to the primary, it is called a step-up transformer. When it is used to “decrease” the voltage on its secondary windings with respect to the primary, it is called a step-down transformer. When a transformer produces the same voltage on both the primary and secondary windings, we say its output are identical with respect to the voltage, current, and power transferred. This type of transformer is called impedance transformer and it is mainly used for impedance matching network or the isolation of adjoining electrical circuits.

TRANSFORMER TURNS RATIO

Assuming an ideal transformer and the phase angles: Φp – Φs

TRANSISTORS

Transistor is a semiconductor device that is used as a switch or an amplifier (amplify weak electrical signals). A transistor is made up of a semiconductor material with three pins (base, collector and emitter) which is connected to external circuit. A current or voltage applied to one pin mostly the base of the transistor terminal controls the current through another pin or pair of terminals. Transistor is the fundamental building block of modern electronic devices.

The most usefulness of a transistor is its ability to use a small signal applied between its base or gate to control to control a much larger output signal. This property is called gain. It can produce a stronger output signal, a voltage or current which is proportional to a weak input signal (base); that is, it can be used as an amplifier. Alternatively, the transistor can also be used as an ON and OFF switch in a circuit. It low input signal (voltage) can be used to switch ON or OFF a high voltage.

There are two types of transistor in a circuit which are BJT (bipolar junction transistor), and FET (field effect transistor). There also the MOSFET (metal oxide semiconductor field effect transistor). A BJT transistor has three terminals labeled the base, collector, and emitter. A small current that is flowing between the base and emitter, can control or switch a much larger current between the collector and emitter. For a FET, the terminals are labeled gate, source, and drain, and a voltage at the gate can control a current between its source and drain. The diagram below shows the circuit symbol of a BJT and MOSFET. The resistor RL represents the load resistance.

     

                                                 (a)                                            (b)

 

                                           (c)                                                                (d)

From the diagrams above, (a) represent BJT circuit symbol transistor, (b) represent MOSFET circuit symbol (C) represent the circuit diagram of using transistor as a switch while (D) represents the circuit diagram of using transistor as an amplifier.

We shall reveal more information about transistors on our next post, and how to test various transistors.