EET 450 – Advanced Digital

Chapter 24Power

Power Supplies Power conversion

Performs a voltage conversion from either 120vAC to desired or 12vDC to desired voltages

Technologies Linear

• Not efficient – heat generated Switching

Power Supplies Power requirements

Supplying adequate power (watts)• Total ~ 150-350 watts

Supply constant voltages• + 5V• -5 V• + 12V• - 12V• +3.3V (ATX)

Power Supplies Device Power needs

Table 24.1 • Floppy – 1.4 W• Video – 6.5 W• HD – 2.2W – 6.5 W• Memory 16.8 W/8M• System Board – 25 W

Supply Voltage US Standard – 115 V – 60 Hz

100-240, 50/60 Hz is common Regulated supplies for AC

Fairly uncommon – complex Regulation is typically done by

converting to DC, regulating, then converting back to AC

Portable Power Batteries

NiCad Lithium Ion NiMH – Smart Battery

Notebook Power 2-6 hours

Power Connections Standard P/S

D shaped device power connector• +5/+12

3.5” power connector• +5/+12

Main Board Power Connector• See tables 24.3, 24.4

Power Management States of APM

Full On APM Standby – memory powered APM Suspend - vegetable Hibernation – allows restoration to

memory/ program state Off State

Energy Star PC Monitor able to switch to a low

power mode. < 30 watts after 15 to 30 minutes

Combo of PC/monitor < 60 watts Printer based on PPM

Power Protection Irregularities

Overvoltage• Surges

Undervoltage• brownout

Noise• RF

Surge Suppression Sinking energy spikes away from PC Sacrificial

MOV Active

Zener Diode

UPS Battery System Backup Power Supply

Regulation and ‘clean’ output waveform

True UPS Continuous power Switching power Computer Interface (network)

Other Considerations Phone Lines Static Electricity Network Interface

Cases The case dictates what can kind of

power supply can be used.

Older case Styles PC/XT –

Small Power Supply (63 watts) AT Style

Desktop Tower Baby AT form factor

LPX Style PS2 Style

Current case styles ATX form factor

Power Supply used in ATX and NLX systems

Power connector is substantially changed

NLX style• Low profile ATX

SFX style Micro-ATX motherboards

Power Supply Connectors Standard M/B connector

AT ATX

Power expansion Y – cable

ATX Auxiliary and Optional connector

Disk Drive Power Connectors Conventional drive

D-shaped New ‘3.5”’ connector

Keyed pin connector