5.power supply

8/3/2019 5.Power Supply

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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



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



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



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



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



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




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




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




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



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



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



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



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



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



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



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



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



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



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



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



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



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



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



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



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



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



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



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.



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



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

5.power supply

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