The Power Supply

1. PC Powe r Supply

2. Power Supply
Block Diagram of Power Supply
The Power Supply Converts AC to DC and regulates the
output voltage to a value required by the load

3. A T Standard
Advanced Technology Standard

4. A T Standard
Output Voltages
Standard
Color
Pin Voltage
P8-1 +5 Orange
P8-2 +5 Red
P8-3 +12 Yellow
P8-4 -12 Blue
P8-5 Ground Black
P8-6 Ground Black
Standard
Color
Pin Voltage
P9-1 Ground Black
P9-2 Ground Black
P9-3 -5 White
P9-4 +5 Red
P9-5 +5 Red
P9-6 +5 Red

5. ATX Power Supply

6. Power Supply
• A power supply (sometimes known as a power supply unit or PSU) is a
device or system that supplies electrical or other types of energy to an
output load or group of loads. The term is most commonly applied to
electrical energy supplies.
At the motherboard
At the Cable
• The most common computer power supply is built to conform with the
ATX form factor. This enables different power supplies to be
interchangeable with different components inside the computer.

7. A T X Connector Standard
• The ATX (for Advanced Technology Extended) form factor was created by
Intel in 1995. It was the first big change in computer case and
motherboard design in many years.
• ATX overtook AT completely as the default form factor for new systems.
ATX addressed many of the AT form factor's annoyances that had
frustrated system builders.
AT POWER CONNECTOR

8. A T X Power Connector
- ATX Power
Supply connector
- Typical wattages range
from 200 W to 500 W
- There are also other,
smaller connectors, most of
which have four wires:
two black,
one red,
one yellow.
“each black wire is a Ground, the red wire is +5 V, and
the yellow wire is +12 V.”

9. A T X
ATX Motherboard Connectors
Pin Voltage Standard Color
1 + 3.3 Orange
2 + 3.3 Orange
3 Ground Black
4 + 5 Red
5 Ground Black
6 + 5 Red
7 Ground Black
8 + 5 Gray
9 + 5 Purple
10 + 12 Yellow
Pin Voltage Standard Color
11 + 3.3 Orange
12 - 12 Blue
13 Ground Black
14 PS_On Green
15 Ground Black
16 Ground Black
17 Ground Black
18 - 5 White
19 + 5 Red
20 + 5 Red
At the motherboard At the cable

10. B T X Connector Standard
• In 2003, Intel announced the new BTX standard, intended as a
replacement for ATX. BTX (for Balanced Technology Extended) is a form
factor for PC motherboards, originally slated to be the replacement for
the aging ATX motherboard form factor in late 2004 and early 2005.
At the motherboard

11. B T X Connector Pin Designation
Pin Signal Description
1 +3.3 VDC
2 +3.3 VDC
3 COM Ground
4 +5 VDC
5 COM Ground
6 +5 VDC
7 COM Ground
8 PWR_OK Power good - indicate that VDC voltages
are in range.
9 +5 VSB Standby voltage
10 +12 VDC

12. B T X Connector Pin Designation
Pin Signal Description
11 +12 VDC
12 +3.3 VDC
13 +3.3 VDC
14 -12 VDC
15 COM Ground
16 PS_ON# Active low. TTL compatible (0.1-0.8V low; 2.0 high?). When low -
DC outputs are enabled. When high - power supply should not deliver DC
current.
17 COM Ground
18 COM Ground
19 COM Ground
20 N/C
21 +5 VDC
22 +5 VDC
23 +5 VDC
24 COM Ground

13. B T X/ATX/AT HDD and FDD Power Connector Pin
Designation
Pin Voltage Color
1 + 12 Yellow
2 Ground Black
3 Ground Black
4 + 5 Red

14. Question
• Can I fit an ATX mainboard in an AT case?
- Not really. An AT case and AT power supply can neither power up nor
house a new ATX mainboard. ATX and AT are two different form-factors.
The AT case was designed before ATX. Most of the computer cases built
before late 1996 were AT form-factor. For over 10 years, from about 1985
to 1997, the AT form-factors, founded by the original IBM PC-AT, provided
the standard for 90% of the PC industry. Today, the majority of new
systems ATX form-factor. The ATX is also known as the Extended AT form-factor.

15. Choosing a Power Supply
Why Weight Matters?
The more appropriate question is why size matters.
The weight of a power supply is directly related to the quantity, quality, and
size of the material (thus cost) used to build the power supply.

16. Choosing a Power Supply
• Conclusions
This brief study clearly confirms an empirical knowledge: the
quality of a power supply can be estimated by its weight.
- The very simple and easy way for ordinary PC users to
estimate and compare the quality of a power supply.

17. Identifying Defective Power
Supply(Dead set)
• For AT Power Supply
Turn on the main power switch(mechanical) and measure the
presence of the output voltage (±12V and ± 5V) using a voltmeter.
If a voltmeter is not available, just observe the functionality of the
cooling fan.
• For ATX and BTX Power Supply
Simply short the Ps_On terminal and observe the cooling fan.
If the fan works, the power supply is good. You can measure the
output voltage of each terminal and compare the reading to the
specified values.
• Replacement of a known good Power Supply is the last approach
for confirmation.