Power Supply Cooling Protection

Objectives :

• Discuss the power supply unit

• Discuss cooling devices for the system

• Protect a system using UPS Backup Power Systems

• Explain the structure and components of SMPS

• Troubleshoot the power supply unit, SMPS and the UPS power problems

Power Supply :

Converts AC to DC to supply various components

Generates high-frequency signals during the electric current conversion from AC to DC

Packed in a metal box to prevent damage to system due to high-frequency signals

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 supplies are operated using different control signals

Different control signals are :

• PG Signal (Grey)

• Power-On (PS_ON) (Green)

• +5VSB (Violet) – always on when AC power input is active, 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

Different Form Factors :

• Personal Computer / Extended Technology (PC/XT) Form Factor – has a toggle switch and can accept 130W of power

• Advanced Technology (AT) Form Factor – accepts 192W of power

• Baby AT Form Factor – small and narrow and used in tower model system. No toggle switch and input power is 192W

• Low Profile Extended (LPX) Form Factor – small in size and also called slimline power supply

• Advanced Technology Extended (ATX) Form Factor – uses NLX power supply. Does not have a power outlet to connect to monitor. uses ATX connector and has 3.3V and +5V stand by (SB) output

• NLX - NLX motherboard also uses a riser board for the expansion of bus slots and uses true ATX power supplies. NLX motherboards can be removed more quickly and easily from their chassis for service because the supply plugs into the riser card and not the motherboard.

• Small Form Factor (SFX) - 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 output of SFX power supply unit is 90W and is used on smaller systems that do not require a lot of power. SFX power supply unit uses the ATX connector to connect to the motherboard

• Workstation Technology Extended (WTX) Form Factor - WTX power supply unit is available in three varieties 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 used in workstations and RAID bays that are used in servers.

Redundant or Hot Swappable Power Supply - Consists of two power supply units. Each unit is capable of supplying power to the whole system. If one power unit fails, the other unit can prevent power loss. The damaged unit can be replaced; this is referred to as hot swapping. You can remove and reinstall one SMPS when the server is in ON

Types of Power supply :

Two types of power supplies :

• Linear power supply - Transforms incoming voltage to a lower voltage using transformers and is bulky

• Switch-mode power supply - Uses high switching frequency. It is compact and can deliver very high power. Used as DC to DC converter and less expensive and lighter transformers 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

Electrical connector used to carry DC or low frequency AC power

Connectors carrying small amount of power are called signal connectors

AT Power Connector - Two 6 wire connectors named P8 & P9 which are to be connected to the mother board with black wires inside. PC/XT, AT, Baby AT and LPX form factors use AT power connectors

ATX Power Connector - 20 pin single connector with mainly 6 types of voltages coming out of it. ATX/NLX form factors use the ATX style power connectors

Standard Peripheral Power Connector (Molex) - Use 4 wire connectors. Hard disk drive, CD/DVD drives use this larger size connectors

Floppy Drive Power Connector (Mini/Berg) - 3.5-inch floppy disk drive use smaller size connectors, called as mini-plug

Cooling Systems :

Cooling devices such as drive coolers and bay coolers are used to cool down the system components such as hard disk

A thermal conductive tape attaches the drive coolers with the hard disk drive. Has a fan that blows air on the hard disk to cool it

Hard disk is placed in the bay cooler that has fans for cooling the device and is mounted in the 5.25-inch drive bay

System produces heat while it is functioning that can damage the internal components of the system

Fans - System case and the system power supply have a fan in it that helps channel air flow in or out from the system case

Heat sink - Heat sink is used to cool the microprocessor and the other chips on the system

Switch Mode Power Supply (SMPS) :

Electronic power supply unit which uses internal control circuit to provide the stabilized output

Used in military and avionic equipment

Different components of SMPS are:

Primary Rectifier – Combination of 4 diodes or rectifier device 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 for converting 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

Secondary Transformer - Secondary transformer is a main bigger transformer and is driven from the collector of the switching transistor

Secondary Rectifier – Consists of two groups of diodes, secondary positive rectifier and secondary negative rectifier used to generate +Vcc and –Vcc voltage

Secondary Filter – Consists of inductors and electrolytic capacitors

Pulse Width Modulator - Designed around the IC TL 494 and some other components

Driver Transistor and Driver Transformer – The switching transistor cannot be driven directly from PWM 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 transistor and driver transistor is coupled using driver transformer

Output Section – Output section of the power supply consists of two 6 pin connectors for the motherboard in AT 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.

Troubleshooting :

Various tools can be used to troubleshoot SMPS problem

Due to a faulty power supply, the components of the system 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