Basic Principle
of Operation
·
45 turns on the primary windings and 15 turns
on the feedback winding.
·
When current flows through the primary windings
of the coil, magnetic flux will be produced. This flux cuts the feedback
windings and causes voltage to be induced in the coils.
·
The polarity of induced voltage in the primary
windings is the opposite of the feedback windings. This causes the voltage from
the feedback windings to be coupled with the base of the transistor. This
effect turns the transistor on more.
·
As the current increases and reaches steady-state,
there will be zero induced voltage and causes an instant collapse of magnetic
flux, causing the voltage in the feedback winding reversed, turning off the
transistor even more. The cycle ends when the transistor is completely off.
·
the transient pulse is generated when
transistor is fully off. The collapsing magnetic flux produces a voltage in the
primary winding.
·
Since the transistor no longer functions, the
energy from the windings is transferred to the high-speed diode. A high voltage
spike is produced and this energy is used to charge up the battery.
·
A whole new cycle will begin when the resistor
on the base turns the transistor on again.
Physic
Laws Involved
The theory of induction and inductance explains
it all. When current flows through a long straight wire, magnetic field is
produced. The Biot-Savart law states
that the current flowing through the conductor and the perpendicular distance
of the point R from the wire affect the magnitude of magnetic field produced.
Diagram 1: Magnetic field due to current
carrying conductor
The same phenomenon happens when the wire is
wound up into a helical coil of wire. This is also known as solenoid. However,
due to the placing of circular wires which are adjacent to each other, there is
an increase in the complexity of the flux produced.
Diagram 2
: Magnetic field in a solenoid
As shown in Diagram 4, there are
circular magnetic field lines being produced surrounding the wires. The
magnetic fields in between each turn is cancelled out as they are in the opposite
direction. Due to this effect, the magnetic fields outside the solenoid are
weak and widely spaced. On the other hand, the magnetic fields which are in the
same direction combines and a stronger resultant field is produced. This
happens in the region of the central axis of the solenoid.
The
magnitude of magnetic field of the solenoid can be determined from Ampere’s
law.
According Faraday’s law of induction, the magnetic field stops
expanding when current reaches steady-state. The magnetic field collapses when
the applied voltage is removed. This induces an emf and current flow which
opposes the polarity of the previous induced emf. This is also known as the
counter emf as a result of the collapsing of magnetic field.
Diagram 3 :
Graphs of voltage and current due to induction
These are the theories behind happening in the
primary windings when current flows through. For the feedback windings, the
reverse process takes place when the magnetic flux of the primary windings cut
through the coils. Current and emf will be induced.
