Transcript From Electric to Electronic

From Electric to Electronic
From the JUs to the Vacuum Tube
Electric vs. Electronic
• Electric circuits are connections of conductive wires and other
devices whereby the uniform flow of electrons occurs.
• Electronic circuits add a new dimension to electric circuits in that
some means of control is exerted over the flow of electrons by
another electrical signal, either a voltage or a current.
• In electronics we are dealing with special devices able to control the
flow of electrons according to another flow of electrons, or by the
application of a static voltage.
• In other words, in an electronic circuit, electricity is able to control
electricity.
IT ALL STARTED WITH THE
FIRST JU…
1st JU
Coil them up!
2nd JU
Current Induced ONLY when
moving!
How do you measure Inductance?
• The ratio of magnetic flux to the current
producing it.
L=Φ/I
Webers/Ampere
s
Inductance is measured in Henries
3rd JU
Joseph Henry (1797-1878) is widely considered the foremost
American scientist of the 19th century. Henry's early investigations
concerned electromagnetic phenomena, and his discovery of
electromagnetic self-induction in 1831 established his reputation in
America. In 1846 Henry was named first Secretary of the newlyestablished Smithsonian Institution, a position he held until his death.
In 1868 he was elected President of the Academy; this position, too,
he held until his death.
Can you picture it?!
Continuing with electronics…
Using electricity to control electricity.
Thomas Alva Edison (February 11, 1847 –
October 18, 1931) was an American inventor,
scientist and businessman who developed
many devices that greatly influenced life
around the world, including the phonograph,
the motion picture camera, and a longlasting, practical electric light bulb. Dubbed
"The Wizard of Menlo Park" (now Edison,
New Jersey) by a newspaper reporter, he
was one of the first inventors to apply the
principles of mass production and large
teamwork to the process of invention, and
therefore is often credited with the creation of
the first industrial research laboratory.
The Precursor to the Vacuum Tube
•
Edison and his team were hard at work trying to
find a light bulb filament that worked well. He
had already settled on a carbonized (burned)
bamboo filament, but even this solution was not
perfect. After glowing for a few hours, carbon
from the filament would be deposited on the
inside walls of the bulb, turning it black.
•
His assistant noticed that the carbon seemed to be coming from the end of
the filament that was attached to the power supply, and seemed to be flying
through the vacuum onto the walls of the bulb.
•
Edison determined that not only was carbon flying through the vacuum, but
that it carried a charge. That is, electricity was flowing not only through the
filament but also through the evacuated bulb.
Thermionic Emission
The flow of charged particles called thermions from a charged metal or a
charged metal oxide surface, caused by thermal vibration energy
overcoming the electrostatic forces holding electrons to the surface of the
atom.
The Edison Effect
How to fix the blackened bulbs?
• Edison tried to “draw” off the discoloration by
placing a metal plate and charging it POSITIVE
• Edison noticed that, with an extra electrode
connected to the positive end of the filament, a
small but measurable electric current flowed
between them. He termed this device an
Electrical Indicator.
• While he was proven to be right about the flow,
Edison could not explain it, and the third
electrode did not prevent blackening of the bulb,
so he moved on to other experiments. But he
did patent the new device, because he believed
that it might have some commercial
applications, such as measuring electric current.
20 years later…
Edison Effect in a vacuum tube was waiting
to do something…
Side Note - Galvanization
• Luigi Galvani – 1783
• Italian physicist and physician
• He was a pioneer in modern obstetrics,
and discovered that muscle and nerve cells
produce electricity.
The Galvanometer
• Galvanometer is the historical name given to a moving coil electric
current detector.
• When a current is passed through a coil in a magnetic field, the coil
experiences a torque proportional to the current.
• If the coil's movement is opposed by a coil spring, then the amount
of deflection of a needle attached to the coil may be proportional to
the current passing through the coil.
• Such "meter movements" were at the heart of the moving coil
meters such as voltmeters and ammeters until they were largely
replaced with solid state meters.
Back to Business Mrs. Houston!
So what about this
Galvano-froggy-thingy?
Aha!
The Fleming Valve
•
Sir John Ambrose Fleming -1904
•
Worked to develop the first rectifier while working for the Marconi
Company.
•
He was faced with the problem of detecting weak wireless signals.
•
He was decided to try inserting one of Edison’s lamps in
an oscillatory circuit containing a galvanometer.
•
He had found the solution to the problem of rectifying
high frequency wireless circuits.
•
Fleming designed a transmitter for to attempt transmission of
radio waves across the Atlantic from Poldhu, England, to
Nova Scotia, Canada.
•
The distance between the two points was about 3,500 kilometres (2,100 miles).
•
This was the start of the wireless revolution.
The Fleming Valve
•
Allowed electrical current to flow in one direction, but not the other.
•
Fleming determined that by changing the position of the
metal plates around the filament he could vary the
strength
of the current.
•
At the receiving end the radio waves were difficult to
detect with a galvanometer, but Fleming realized that if
he could get the current to flow in only one direction,
the oscillations of the wireless signal could be read easily.
He did this by adding a positively charged plate separate
from the filament to the Edison tube.
•
Fleming Valve, Diode Valve, Fleming Diode,
Thermionic Valve, Oscillation Valve.
•
It becomes known as a 'vacuum tube' in America
How The Fleming Valve Works
Positive voltage
on the plate
attracts electrons
from the filament.
Current flows!!!
+
-
A negative charge to
the plate causes the
current to cease.
They are repelled by
like charges.
Going One Way!
• The creation of the Fleming diode
opened up electrical technology to both
alternating current and direct current.
• Although now superceded by
transistors and integrated circuits in
electronic applications, diodes are still
used in high-power transmitters,
sensitive optical applications, and
audio amplifiers.
• Rectification:
– To convert alternating current into direct
current.
But Wait… There’s More!
Modulation & Amplification!
•
Lee de Forest – 1906
•
Modified Fleming's Valve by adding a grid to control
and amplify signals, and called his device the Audion.
•
His Audion tube, a three-electrode device
(plate, cathode, control grid), was a vacuum tube
which allowed for amplification for radio reception.
•
This "grid" was a bent wire between the plate and filament. de Forest discovered that
if he applied the signal from the wireless-telegraph antenna to the grid instead of the
filament, he could obtain a much more sensitive detector of the signal. In fact, the grid
was changing ("modulating") the current flowing from the filament to the plate.
•
This device, the Audion, was the first successful electronic amplifier. It was the
genesis of today's huge electronics industry.
•
Audion, Triode
How A Triode Works
Apply a like charge to the grid and the flow stops!!
(It’s that magnetism thing at work again!!!)
So What?!
•
A small electric current applied to the grid would result in the proportionate
flow of a much larger current from the filament to the plate- in other words,
amplification.
•
The Audion became know as the Triode and was the standard means of
amplification until it was gradually replaced by the transistor in the 1950's and
60's.
•
Without the Audion, inexpensive amplification of wireless voice transmissions
would not have been possible, and Radio Corporation of America would have
been a significantly different enterprise.
Modulation
• the process of varying a periodic waveform in order to use that
signal to convey a message
• to vary the amplitude, frequency, or phase of (a carrier wave or a
light wave) for the transmission of information (as by radio)
Amplification
•
increasing the power and/or amplitude of a signal.
•
Taking power from a power supply and controlling the output to match the input
signal shape but with a larger amplitude.
•
In this sense, an amplifier may be considered as modulating the output of the power
supply.
Who’s Your Daddy?!
• Lee de Forest
The father of radio