The document discusses CD-ROMs and how they work. It describes that CD-ROMs use lasers to read digital data stored as pits and lands on the disc's reflective layer. When the laser hits a land, light reflects back and is detected as a 1, while a pit scatters light and is detected as a 0. The binary data is then converted back to sounds or other digital information that can be understood by the computer.

1. There are basically two types of storage devices
 Magnetic storages(hard disk drive)
 Optical storages(CD-ROM)

2.  Compact disk-read only memory.
 It is an optical disk used to store digital data,
originally developed for storing digital audio.
 A CD is flat, round, portable metal disc, which
is coated with a thin metal or plastic or other
material that is highly reflective.

3.  A CD-ROM drive operates by using a laser to
reflect light off the bottom of the CD or disc.
 The reflected light pulses are read by a photo
detector.
 These incoming pulses are decoded by the
microprocessor and then sent as usable data to
the rest of the computer where it is processed
and used.

5. It's actually made of three layers.
1. CD is made from a tough, plastic
called polycarbonate.

6. 2. Sandwiched in the middle there is a thin layer
of aluminum called reflecting layer and this
reflecting layer stores data. It's shiny so that
a laser beam can bounce off the disc and read the
information stored on it.
3. Finally, on top of the aluminum, is a protective
layer of plastic and lacquer.
The dull side usually has a label on it telling you
what's on the CD

7.  Photocells are sensors that allow you to detect
light. They are small, inexpensive, low-power,
easy to use and don't wear out.
 They are often referred to as CDS cells (they are
made of Cadmium-Sulfide), light-dependent
resistors (LDR), and photo resistors.
 They used in toys, gadgets and appliances

8.  The information to be stored is digitized, that is, the
data can be represented by binary numbers, which are
made up of '1' and '0' digits. This information is stored
on the metal layer. The data is represented using pits
(1) and space between pits is called land (0).
 Lands are flat areas on the metal surface
 Pits are depression or bumps

9. Step1:: Inside your CD player, there is a laser beam
(called a semiconductor diode laser) and a
small photoelectric cell (an electronic light detector).
Step2:: When you press play, an electric motor
makes the disc rotate at high speed (up to 500rpm).
Step3:: The laser beam switches on and scans along a
track, with the photocell, from the center of the CD to
the outside

10. Step4:: The laser flashes up onto the shiny side of
the CD, bouncing off the pattern of pits and lands
on the disc. The lands reflect the laser light straight
back, while the pits scatter the light.
Step5:: Every time the light reflects back, the
photocell detects it, realizes it's seen a land, and
sends a burst of electric current to an electronic
circuit that generates the number one.

11.  A transition from a land to pit or pit to land is
1.
 Absence of transition is interpreted as 0.

12. Step6:: When the light fails to reflect back, the
photocell realizes there is no land there and
doesn't register anything, so the electronic circuit
generates the number zero.

13. Step7:: Another electronic circuit in the CD player
(called a digital to analog converter or DAC) decodes
these binary numbers and converts them back into a
changing pattern of electric currents.
Step8:: A loudspeaker transforms the electric
currents into sounds you can hear (by changing their
electrical energy into sound energy).

14.  There are no pits and lands imprinted on
plastic. Instead, in between the protective
polycarbonate and the reflective aluminum,
there's a layer of dye.
 A CD-R writer has a higher-powered laser than
normal, which generates heat when it strikes
the disc, "burning" the dye and making a tiny
black spot.

15.  Later, when a CD reader aims its laser at that
spot, the light is completely absorbed and
doesn't reflect back. This indicates that a zero
("0") is stored on the disc at that point.
 In places where the dye is unburned, the laser
light reflects straight back again, indicating that
a "1" is stored on the disc.

16.  By creating areas of "burned" dots, and other
places where the dye is left alone, a CD-R
writer creates a pattern of binary zeros and
ones that can be used to store information.
Unfortunately, once the dye is "burned" it's
permanently transformed: you can't change it
back again. And that's why you can only write
a CD-R disc once.

18.  Regulated power supply
 Unregulated power supply
Unregulated power supply
 The output voltage is not constant. It will
vary with the input voltage and the load
current.

19. Regulated linear power supplies
 Regulated linear power supplies are same to
the unregulated linear power supply except
that regulator/stabilizer is used in place of the
bleeder resistor.
 The main aim of this supply is to provide the
required level of DC power to the load. The
DC power supply uses an AC supply as the
input

20.  switched-mode power supply is an
electronic power supply that incorporates
a switching regulator to convert electrical
power efficiently.
 SMPS transfers power from a DC or AC source
to DC loads.
 SMPS always provide a well regulated power
to the load irrespective of the input variations.

21. SMPS schematic diagram

22. SMPS working
1. Rectifier:: The SMPS has an AC input, then its first job is to
convert the input to DC. This is called rectification. A SMPS with
dc input does not require this stage.
• The rectifier produces unregulated(high voltage DC) dc which
is then passed through the filter circuit.
• Hence the high AC becomes High Voltage DC from this
operation we eliminate high spikes, surge and ripple effect.

23. 2. Chopper:: A chopper is basically a dc to dc
converter whose main function/usage is to create
adjustable dc voltage from fixed dc voltage
sources
i. A DC chopper is a static device that converts
fixed dc input voltage to a variable dc output
voltage directly.

24. ii. AC Link Chopper
In the case of an ac link chopper, first dc is
converted to ac with the help of an inverter. After
that, AC is stepped-up or stepped-down by a
transformer, which is then converted back to dc
by a diode rectifier. Ac link chopper is costly,
bulky and less efficient as the conversion is done
in two stages.

25. 3. Flyback or Output transformer(step-down transformer)
If the output required is to be isolated from input, the
inverted AC is used to draw the primary winding of a
high frequency transformer.
IT inverts AC voltage up to down to the required output
level.
4. Output rectifier and filter : If the DC output is
required, the AC output from transformer is rectified.
it gives Rectified constant DC output Voltage without
current fluctuations.

26. 5. Chopper controller: feedback circuit monitors
the output voltage and compare it with the
reference voltage.
 Some portion of output is taken as feedback
signal and this signal compared with reference
voltage and the error (if present) is amplified
depends on the error chopper controller
changes its frequency hence the switching
device regulates the output. So the minimum
changes in output DC regulated instantly
without affecting load.

27.  The full form of the UPS is an uninterruptible
power supply.
 It is an electrical device, gives emergency power
to various loads when the input power typically
fails.
 The main purpose of a UPS is to provide a
protection to the equipment like computers,
electrical equipment, when there is a power
disruption.

28.  Charger card:: it contains rectifier which
convert AC to DC to charge the battery
 Inverter card:: It convert DC to AC

29.  EMI( electromagnetic interference) filter helps
to reduce the electric noise.
 Stabilizer:: regulate the voltage to the constant
range that is safe for the loads.

30.  Display card and buzzer::
Led are used to indicate the status of UPS
Status: overloading ,charging, online/offline
 Buzzer: is used to give warnings like:
Low battery
Overloading
 FAN:: It is used for the cooling the fan system.

32.  Battery: UPS battery is used as a storage device,
which consists of several cells in series with a
capacity to maintain its size determine the is
charge time. its main function: when the
electricity is normal the energy converted into
chemical energy stored in the battery internal,
when the electricity us fail the chemical energy
into electrical energy provided to the inverter o
the load.

33.  Static switch: s1 –generally OFF
s2- always ON
 Inverter card is always active
 When inverter fails S1-ON
 It always remains on battery, whether input supply is
present or not.
 It uses its battery throughout the time when the electronic
device is in use. Therefore the battery is always used here.

34.  The online UPS is connected to the main load at all the
time or until the battery in it gets charged. In this case,
our electronic device gets the power from the online
UPS and not directly from the AC main supply. So,
even when the main AC fails, our electronic device’s
operations need not be stopped.

35.  Input is directly connected to output
 Switches: s1 normally ON
s2 OFF
When main fails s2 ON
It never uses the battery until there is a power failure.
Therefore the battery is rarely used here.

36.  It is required only when the main power
supply fails. Yes, in this case, the electronic
device gets power directly from the main AC
power supply and not from the UPS. When
there is any voltage surge or fluctuation in the
main input power, then the offline UPS
supplies power to the electronic devices.
Therefore, these kinds of UPSs are required
only during power failures and not all the time.
 One of the best examples for offline UPS is the
desktop computers.