Smps stands for “switch mode power supply”. Power
Supply is an electrical device that provides power to electronic device and
circuits. Most of the electronic device require less power DC voltages as
compared to the voltage supplied to home or office.
SMPS supplies power to different system components
such as the motherboard and the device drives. The main components of SMPS are
power connectors and power supply fan. Power connectors provide DC voltage to
all the system components and power supply fan is used to keep the unti cool.
Switch
mode power supply :-
Also called switching power supplies and sometimes
chopper controlled power supplies, SMPSs use high frequency (relative to 50/60
Hz) switching devices such as Bipolar Junction Transistors (BJTs), MOSFETs,
Insulated Gate Bipolar Transistors (IGBTs), or Thyristors (SCRs or triacs) to
take directly rectified line voltage and convert it to a pulsed waveform.
Most small SMPSs use
BJTs or MOSFETs. IGBTs may be found in large systems and SCRs or triacs are
used where their advantages (latching in the on state and high power
capability) outweigh the increased complexity of the circuitry to assure that
they turn off properly (since except for special Gate Turn Off (GTO)
thyristors, the gate input is pretty much ignored once the device is triggered
and the current must go to zero to reset it to the off state.) The input to the switches is usually either 150-160 VDC after rectification of 115 VAC, or 300-320 VDC after doubling of 115 VAC or rectification of 220-240 VAC. Up to this point, there is no line isolation as there is no line connected (large, bulky, heavy) power transformer.
Specifications
of SMPS :-
To identify various
SMPPs, you need to consider certain factors such as size, wattage and different
connectors. The factors are
Size– power supplies are available in
various sizes. Selecting a power supply, you need to select power supply of
appropriate size which can fit in your system case.
Connectors :-
check for the available number of power supply connectors that can provide
supply to all the device. More number of connectors are better.
Wattage :- servers and desktop computers work in power
rating. Power rating is measured in terms of watts. Rating for SMPS varies
between 250w – 600w. maximum power
consumption occurs at start up time of SMPS. Computers have rating between
250w – 500w and servers have rating between 400w -600w. it is always
better to have excess wattage on power supply.
Working &functions of SMPS:-
A typical line connected power supply must perform
the following functions:
- Voltage
conversion - changing the 115/230 VAC line voltage into one or more other
voltages as determined by application.
- Rectification
- turning the AC into DC.
- Filtering -
smoothing the ripple of the rectified voltage(s).
- Regulation
- making the output voltage(s) independent of line and load variations.
- Isolation -
separating the supply outputs fro
Form factors of SMPS :-
The form factor of power supply represents the size
and the shape of power supply. The different form factors of the power supply
unit. They are
LPX :- lpx is standard “low profile extended”. It
is also known as slim line form factor because its cases are known as slim line
cases. The main goal of this form factor is size reduction. Because of its
small size and convenient rectangular shape, LPX can put into all sorts of
cases. The LPX form factor is found in low-profile cases with a riser card
arrangement for expansion cards where expansion boards run parallel to the
mother board.
SFX :- sfx is standard “small form factor”. The sfx
power supply unit has two fans to cool the whole system. This additional fan is
placed on the top of the power supply. The internal fan of the sfx power supply
is thermally speed- controlled. The output of sfx power supply unit is 90w and
is used on smaller systems that do not require a lot of power. The sfx power
supply unit uses the atx connector to connect to the motherboard. The one
difference here is that the sfx power supply specification does not support the
-5v compatibility voltage.
SMPS Voltages & Color Codes
LPX, ATX, SFX SMPS Connectors, voltages and functions
There are three types
of SMPSs. They are LPX, ATX, SFX. These three types of SMPSs have
different connectors and each wire has different voltages. Here the
connectors and its voltages.
Output
Voltages
Smps
LPX
ATX
SFX
Red
+5v
+5v
+5v
Yellow
+12v
+12v
+12v
Blue
-12v
-12v
-12v
White
-5v
-5v
-5v
Black
0v
0v
0v
Orange
+5v
+3.3v
+3.3v
Green
----
+5v
+5v
Gray or
Brown
----
+5v
+5v
Purple
----
+5v
+5v
Power supply
control signals
Red : it
is used for signal sending
Yellow
: It is used for motor running
White
&Blue : It is used for backward
compatibility
Black
: It is used for grounding purpose
Orange
: It is used for
power good signal
Green
: It is used for power supply on in ATX
Gray
& Brown : It is used for power good
signal in ATX
Purple
: It is used for auto shutdown in ATX
-12v (Blue) – it is required by some of the serial ports. It
is required by very few serial ports and is provided to maintain compatibility
with such hardware.
-5 v(white)-
it is required by some older floppy controllers and is a bus cards. It is
provide for compatibility with older hardware.
0 v(black)- it is
required to complete a circuit with other voltages. It is ground voltages and
is also known as earth.
+3.3 v(orange)- it is required by the processors, dims, pci/agp
cards. This voltage was introduced in the atx form factor and is available in
the atx/nlx,sfx and wtx form factor.
+5(red)-
it is required by the disk drive logic, voltage regulators, is a cards, simms
and other miscellaneous components of the system. This is the basic supply
voltage for nearly all electronic components.
+12 v- It is required by motors in the system, from drive
motors to cooling fans. It is also distributed to the to the system bus slots
for usage by cards which may need it.
Power supply conrol signals :-
Earlier, mechinanical switches were used to turn the
computer on and off. But now power supplies are operated using different
control signals on the motherboard. The three control signals are :
PG signal (gray) :-
indicates to the motherboard that all the
supplies(+12v,+5v,-12v,-5v,-12v,-5v,and +3.3v) given are at proper level. It
also informs the computer that power supply is working properly and prevents
computer from operating on improper voltages levels.
Ps-on(green) :-
controls the power supply and is part of atx standard. Power on carries a
low-voltage logic-level signal from the motherboard to the power supply, that
indicates when to turn on and off.
+5vsb(violet) :- supplies line that is used to power standby
circuitry, such as the ps_on circuit and the wake-on-lan. The +5vsb line is a
+5v volt supply. It is always on when the pc power input is active, even if the
system is turned off.
Connectors
of smps :- smps provides current to the motherboard,
hard disk drive, and various other components of a system using the power
connectors. Power connector is an electrical connector used to carry DC voltages. There are 5 types of connectors.
Atx power connector
24
pin smps connector
Standard
peripheral power connectors (molex)
Sata
power connectors
Pci-e
6 pin connector
ATX power connector :- This is a 20 pin connector with 6 types of voltages coming out of it. The atx
style power connectors are for the atx/nlx power supply. Atx/nlx form factor
uses the atx style power connectors. This style has a single 20- pin
connector.the color on the pin denotes the color of the wires and gives the
respective voltages.
24 pin smps
connector :-
The 24 pin smps connector is built with atx
style of power connector. This connector is used to provide power supply to the
motherboard. That it is called as pc main power connector. The 24 pin smps
connector has 4 additional pins which carry a different voltage level as
compared to 20 pin connector. Pin number 11,12,and 23 carry the voltage +12 v,
+3.3 v, +5 v respectively and pin number 24 is used as ground.
Standard peripheral power connector (molex) :- The disk drive power connector use 4 wire
connector which are commonly called molex connectors. The hard disk drive,
cd/dvd drives use molex connector.
The ATX 4 pin power supply
connector is a standard motherboard
power connector used to provide +12 VDC to the processor voltage regulator.
Pin
|
Name
|
Color
|
Description
|
1
|
COM
|
Black
|
Ground
|
2
|
COM
|
Black
|
Ground
|
3
|
+12VDC
|
Yellow
|
+12
VDC
|
4
|
+12VDC
|
Yellow
|
+12 VDC
|
Sata power connector :- The sata standard specifies a power
connector which is different from those used by pat drives and many other
computer components that is molex connector. It is a 15 pin connector. The
large number of pins are used to supply three different voltages +3.3v,+5v,+12v.
Each voltage supplied by three pins ganged together
and pins for ground. This is because the small pins cnnot supply sufficient
current for some devices. One pin form each of the three voltages is also used
for hot plugging.
Pci –e 6 pin connector : - pci-e cable is used to provide extra 12 volt
power to pci express expansion cards. Pci express motherboard slots can provide
a maxium of 75 watts. Many video cards draw significantly more than 75 watts so
the 6 pin pci express power cable was
created. These high power cards raw most of their power from the 12 volt
supply. Some times called pci express cables or peg cables.
Troubleshooting
of SMPS :-
A power supply unit is the vital component of a
system that supplies power to various components of the system. The power
supply unit consists of electronic components and may show some problems due to
which the system may not start. Due to a faculty power supply, the other
components of the system may also get damaged. As a result, troubleshooting the
power supply problems is also get damaged an essential task for maintaining the
system.
Troubleshooting pc problems related to SMPS :-
You can troubleshoot basic system problems of the pc related to smps. The system may stop functioning after some time due to a power supply problem.
trobuleshoot when pc did not starting:-
I. If
your PC is not starting then it may be a problem related to power supply.
II.
Check the AC line.
III.
Check the power cord continuity check
using multimeter and line voltage selector switch whether it has been set to
230VAC.
IV.
Open the system case.
V.
Remove all the connectors from drives
and motherboard.
VI.
Short pin no.14 & 15
VII.
Check the PG signal (+5 VDC Gray) if PG
signal is OK means all the output voltages are at proper level.
VIII.
If the SMPS does not work when connected
to motherboard then check whether there is a problem with SMPS.
In
case of a defect or problem with power supply, it is not recommended that an
inexperienced user open a power supply for repairing. The power supply has
dangerously high voltage. Even after unplugging, power supplies can retain
dangerous voltage and must be discharged (like a monitor) before servicing it.
These internal repairs are not recommended unless the technician is specially
trained to repair such components.
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