Power Supply
The basic function of power supply is to convert the AC supplies available at wall socket, that
which is unusable by the computer. The SMPS in a conventional desktop system is designed to
convert the 220V AC, 50 HZ into +5V, -5V, +12V, -12V and +3.3 V DC.
Types of Power Supply
1.
Linear Power Supply
2.
SMPS Power Supply
Linear Power Supply
In Linear power supply the input AC voltage is first stepped down through step down
transformer, approximately to a required voltage and then applied to a bridge rectifier diodes.
The regulation is achieved by sending the DC through series pass Transistor and changing the
current flowing through it, by an error voltage obtained from a comparator (sensing) circuit. Or
a regulator IC output is applied to the base of series pass transistor that determines the amount of
current that has to flow through it to keep the output voltage constant. The excess current
flowing the series pass transistor is converted to heat to achieve regulation. A lot of power is
wasted in the form of heat.
Power Supply
Power Supply
In a personal computer (PC), the power supply is the metal box usually
found in a corner of the case. The power supply is visible from the back of
many systems because it contains the power-cord receptacle and the
cooling fan.
This is a power supply removed from its PC case. The small, red switch at
right, above the power-cord connector, is for changing line voltages in
various countries.
COMPARISON OF LINEAR AND SMPS POWER
S u i tabl e for
Low
powe r
appl i cati o
n
Hi gh
powe r
appl i cati o
n
S m al l
Bi g
Li gh t
He avy
Powe r s u ppl y s i z e -
Bi g
S m al l
W e i gh t -
He avy
Li gh t
Re gu l ati on provi de d to
i n pu t Vol tage ran ge of
O u tpu t
Vol tage
re gu l ati on
Load re gu l ati on
180 V
240V
Le s s
Le s s
Hi gh
Harm on i c In te rfe re n ce
Low
Hi gh
He at an d powe r l os s to
Hi gh
Ne gl i gi bl e
Eas y
Di ffi cu l t/C
om pl i cate d
1
In
l ow
appl i cati on
s u ppl y s i z e W e i gh t -
powe r
powe r
2
Hi gh powe r appl i cati on
3
4
5
6
to 85V
280V
Hi gh
to
7
8
Mai n tai n re gu l ati on
Trou bl e s h ooti n g
9
10
Ri ppl e
O /P
pre s e n t
in
th e Le s s
Hi gh
Block Diagram of SMPS
Power Supply
In this photo you can see three small transformers (yellow) in the center. To the
left are two cylindrical capacitors. The large finned pieces of aluminum are heat
sinks. The left heat sink has transistors attached to it. These are the transistors in
charge of doing the switching -- they provide high-frequency power to the
transformers. Attached to the right heat sink are diodes that rectify AC signals
and turn them into DC signals.
Power Supply
The interior of a power supply
Power Good Signal
Power Good Signal
The power supply sends Power Good signal to the motherboard. If this
signal is
not present, the Computer does not run. The effect of this setup is that
when the
AC voltage dips and power supply becomes over-stressed or overloaded,
the
Power Good Signal goes down and forces a system reset or complete
shutdown.
AT Motherboard connector details
Power Supply
A PC power supply removed from its PC case. Cables and
connectors at right supply DC voltages
Power Supply
Personal computer power supply label.
VSB is the standby voltage provided to the power switch
.
Power Supply
PC Item
Watts
Accelerated Graphics P ort (AGP ) card
20 to 30W
P eripheral Component Interconnect (P CI) card
small computer system interface (SCSI) P CI
card
5W
floppy disk drive
5W
network interface card
4W
50X CD-ROM drive
10 to 25W
10W per
128M
RAM
20 to 25W
to 11W
5200 RP M Intelligent Drive Electronics (IDE) hard 5
disk
drive
7200 RP M IDE hard disk drive
5 to 15W
M otherboard (without CP U or RAM )
20 to 30W
550 M Hz P entium III
30W
733 M Hz P entium III
23.5W
300 M Hz Celeron
18W
600 M Hz Athlon
45W