5.power supply
TRANSCRIPT
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Objectives:
Power supply unit
Cooling devices for the system
Protect a system using UPS Backup Power Systems
Structure and components of SMPS
Troubleshoot the power supply unit, SMPS and theUPS power problems
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Power Supply:
Accepts the Alternate Current (AC) current from thepower socket in the wall and converts the AC current tothe Direct Current (DC). Now a days power supplies areavailable in the range of 250W to 400W
Supplies 3.3V, 5V, and 12V to the different componentsof the system
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Functions of the Power
Supply: Converts AC to DC to supply various components
Generates high-frequency signals during the electriccurrent conversion from AC to DC
Packed in a metal box to prevent damage to systemdue to high-frequency signals
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Output Voltages:
Various voltages provided by the power supply are:
-12 V (Blue) – required by some of the serial ports
-5 V (white) – required by some older floppy
controllers and ISA bus cards 0 V (Black) - ground
+3.3 V (Orange) – required by processor, DIMMs,PCI/AGP cards
+5 V (Red) – required by voltage regulators, ISA
cards, SIMMs and disk drive logic +12 V (Yellow) – used by drive motors and cooling
fans
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Power Supply Control
Signals:
Power supplies are operated using different controlsignals
Different control signals are:
PG Signal (Grey)
Power-On (PS_ON) (Green)
+5VSB (Violet) – always on when AC power input isactive, even if the system is turned off
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Form Factors of Power
Supply: Represents size and shape of the power
supply
Must match the form factor of the system
case and the motherboard
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Form Factors of Power
Supply:
Different Form Factors Personal Computer / Extended Technology (PC/XT)
Form Factor – has a toggle switch and can accept130W of power
Advanced Technology (AT) Form Factor –
accepts192W of power
Baby AT Form Factor – small and narrow and usedin tower model system. No toggle switch and inputpower is 192W
Low Profile Extended (LPX) Form Factor
–small insize and also called slimline power supply
Advanced Technology Extended (ATX) Form Factor – uses NLX power supply. Does not have a poweroutlet to connect to monitor. uses ATX connectorand has 3.3V and +5V stand by (SB) output
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Form Factors of Power
Supply:
NLX - NLX motherboard also uses a riser board forthe expansion of bus slots and uses true ATX powersupplies. NLX motherboards can be removed morequickly and easily from their chassis for servicebecause the supply plugs into the riser card and notthe motherboard.
Small Form Factor (SFX) - SFX power supplyunit has two fans to cool the whole system. Thisadditional fan is placed on the top of the power
supply. The output of SFX power supply unit is 90Wand is used on smaller systems that do not require alot of power. SFX power supply unit uses the ATXconnector to connect to the motherboard
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Form Factors of Power
Supply:
Workstation Technology Extended (WTX) FormFactor - WTX power supply unit is available in threevarieties such as 460W, 610W and 800W with a
single fan or double fans for cooling the system.Large in size and has a powerful output so it is usedin workstations and RAID bays that are used inservers.
Redundant or Hot Swappable Power Supply - Consists
of two power supply units. Each unit is capable ofsupplying power to the whole system. If one power unitfails, the other unit can prevent power loss. Thedamaged unit can be replaced; this is referred to as hotswapping. You can remove and reinstall one SMPS
when the server is in ON condition
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Types of Power supply:
Two types of power supplies:
Linear power supply - Transforms incoming
voltage to a lower voltage usingtransformers and is bulky
Switch-mode power supply - Uses highswitching frequency. It is compact and can
deliver very high power. Used as DC to DCconverter and less expensive and lightertransformers can be used in SMPS design
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Components of the Power
Supply: Power supply unit consists of different functional
components
Different components of the power supply are:
Power Connectors Power Switches
Power supply Fans
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Power Connectors:
Electrical connector used to carry DC or low frequencyAC power
Connectors carrying small amount of power are called
signal connectors Types of
connectors
AT power
connectors
ATX power
connectors
Standard
Peripheral
connector
Floppy
Drive power
connectors
2/3 Pin Mini
Plug type
connectors
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Power Connectors:
AT Power Connector - Two 6 wire connectorsnamed P8 & P9 which are to be connected tothe mother board with black wires inside.PC/XT, AT, Baby AT and LPX form factors useAT power connectors
ATX Power Connector - 20 pin single
connector with mainly 6 types of voltagescoming out of it. ATX/NLX form factors use theATX style power connectors
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Power Connectors:
Standard Peripheral Power Connector(Molex) - Use 4 wire connectors. Hard
disk drive, CD/DVD drives use this largersize connectors
Floppy Drive Power Connector
(Mini/Berg) - 3.5-inch floppy disk driveuse smaller size connectors, called asmini-plug
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Power Switches:
Used to switch power supplyfor system on and off
PC/XT systems have powerswitch at rear end of thesystem
AT tower system cases havepower switch placed on frontside of system case
The ATX system cases useelectronic power switches andthe switch circuitry connectsthe motherboard with thisswitch
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Power Supply Fan:
Used for cooling the system
Located at rear end of power supplyunit
Ball bearing fans are more reliableand are long lasting as compared tosleeve bearing fans
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Factors to be considered
before selecting power
supply: Size – Should fit in your system case
Connectors – No. of connectors should
be more Wattage – Computers have rating
between 300 – 350W and servers have
rating 350 –
400W
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Cooling Systems:
Cooling devices such as drive coolers andbay coolers are used to cool down the systemcomponents such as hard disk
A thermal conductive tape attaches the drivecoolers with the hard disk drive. Has a fanthat blows air on the hard disk to cool it
Hard disk is placed in the bay cooler that hasfans for cooling the device and is mounted inthe 5.25-inch drive bay
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Types of Cooling Systems:
System produces heat while it isfunctioning that can damage theinternal components of the system
Fans - System case and the systempower supply have a fan in it that helpschannel air flow in or out from thesystem case
Heat sink - Heat sink is used to cool themicroprocessor and the other chips onthe system
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Power Protection and
Backup: Must be equipped with protection tools to handle
various power problems
System can be protected using UPS and surge and
spikes can be removed using surge suppressors Problems that may occur are:
Black out – total power failure
Brown out – power falls below 105V AC
Spikes –
caused by lighting strike and last for fewseconds
Surges – caused by motors or AC turns on and offand lasts for few milliseconds
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Protecting a System using
Backup Power Systems: UPS is a device which maintains
continuous supply of electric powerto the connected equipment bysupplying power from a batterywhen main power is not available
In the event of a power failure,using the backup power supply, thesystem can safely shutdown.
UPS ensures that the files on thesystem or the system componentssuch as the hard disk do not getcorrupted due to impropershutdown
Battery of the UPS gets chargedwhen the system is powered on
using the main power supply
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Features of UPS:
Form Factor – Available in stand alone and rack-mount model
Capacity & Run time – Amount of time battery of UPSprovides electric current
Power Conditioning – Ensures that the system isprotected from power surges
Self-test – Ensures that UPS is functioning properly
Automatic Shutdown –
Instruct operating system toshutdown the system automatically when batterypower lowers
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Types of UPS:
Functions of UPS differ from one UPS to another
Different types of UPS are:
Standby UPS – Remains in standby mode until
battery current is required when there is a powerfailure
Line-Interactive UPS – Supplies power to system ifvoltage falls very low
Online UPS – Supplies power to system from UPS
battery at all times even when power supplyvoltage is at normal levels
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Selecting a UPS:
Factors considered before selecting a UPS are:
Load
Installation location – generate noise
Cooling –
use air cooler Location of Batteries
Efficiency – calculate operating cost
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Switch Mode Power
Supply (SMPS): Electronic power supply unit which uses
internal control circuit to provide the stabilizedoutput
Used in military and avionic equipment
Functional block diagram of SMPS
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Components of SMPS:
Different components of SMPS are:
Primary Rectifier – Combination of 4 diodes or rectifierdevice having 4 terminals. Can be combined in pairs
inside TO220 type packages Primary Filter – Consists of big size electrolytic
capacitors of higher voltage capacity. Responsible forconverting the pulsating DC current into almost DC
current Switching Transistor – Consists of a pair of switching
transistors, which are rectangular power transistors.These are fixed on the heat sink Often BU or 2SC/2SD
numbers transistors are used for this purpose
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Components of SMPS:
Secondary Transformer - Secondary transformer isa main bigger transformer and is driven fromthe collector of the switching transistor
Secondary Rectifier
–Consists of two groupsof diodes, secondary positive rectifier and
secondary negative rectifier used to generate+Vcc and –Vcc voltage
Secondary Filter – Consists of inductors andelectrolytic capacitors
Pulse Width Modulator - Designed around theIC TL 494 and some other components
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Components of SMPS:
Driver Transistor and Driver Transformer – Theswitching transistor cannot be driven directly fromPWM IC because output of PWM IC is very less.Therefore, the user needs a driver circuit between the
switching transistor and PWM IC. The power transistorand driver transistor is coupled using driver transformer
Output Section – Output section of the power supplyconsists of two 6 pin connectors for the motherboard inAT power supply, four 4 pin connectors for HDD, FDD
& CD ROM drive Power Good Signal - This section is either designed
around IC 339 or simply with a BC147 transistor.
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SMPS Functional ICs:
TL494
Used for control of Pulse Width Modulation (PWM)regulator
Controls switching of transistors Q1 and Q2 and ON& OFF timers of transistors
LM 339
Generates power good signal and ensures output
voltage levels have their correct values
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Troubleshooting:
Various tools can be used to troubleshoot SMPSproblem
Due to a faulty power supply, the components of thesystem may also get damaged
Problem that may occur are:
System is not starting
Power supply fan is not working
Fuse is blown Power supply is dead
SMPS voltage drops or increases
Fan moves for a moment and then stops