Enhance ATX12V Version 1.3 Power Supply Design Guide
ATX12V
Power Supply Design Guide
Version 1.3
Revision History
Version Release Date Notes
1.0 Feb, 2000 • Public release
1.1 Aug, 2000 • Increase 3.3 V current; add more explanation for power sharing;
do minor edits and format fixes
1.2 Jan, 2002 • Section 3.2.3 Typical Power Distribution. Change +5V loading on
all power supplies distribution tables defined in DG to 0.3A
• Section 3.3.2 PS_ON# . Add text “The power supply should not
latch into a shutdown state when PS_ON# is driven active by
pulses between 10ms to 100ms during the decay of the power
rails.”
• Section 3.2.3.2 Remove –5V from all power distribution tables.
1.3 April, 2003 • Update Power and Current guidance
• Added efficiency guidance at typical and light load
• Increased min efficiency at full load from 68% to 70%
• Serial ATA connector definition added
• Acoustic levels added for low noise power supply design
• Reformat and update revision table
• Update Disclaimers
• Remove guidelines for ATX
• Remove guidance for –5V rail
ATX12V Power Supply Design Guide
Version 1.3
• Updated guidance for Energy Star and stand by efficiency
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ATX12V Power Supply Design Guide
Version 1.3
Contents
1. Introduction.....................................................................................................................6
1.1. Scope ...........................................................................................................................6
1.2. ATX12V as Compared with ATX Power Supply ..................................................................6
1.2.1. Key Changes for ATX12V Version 1.3..................................................................6
2. Applicable Documents.................................................................................................7
3. Electrical...........................................................................................................................8
3.1. AC Input ........................................................................................................................8
3.1.1. Input Over-current Protection...............................................................................8
3.1.2. Inrush Current Limiting ........................................................................................8
3.1.3. Input Under-voltage.............................................................................................9
3.1.4. Regulatory.........................................................................................................9
3.1.5. Catastrophic Failure Protection............................................................................9
3.2. DC Output.....................................................................................................................10
3.2.1. DC Voltage Regulation........................................................................................10
3.2.2. Remote Sensing ................................................................................................10
3.2.3. Typical Power Distribution ...................................................................................10
3.2.4. Power Limit / Hazardous Energy Levels................................................................13
3.2.5. Efficiency ..........................................................................................................14
3.2.6. Output Ripple/Noise...........................................................................................15
3.2.7. Output Transient Response.................................................................................17
3.2.8. Capacitive Load..................................................................................................17
3.2.9. Closed-loop Stability...........................................................................................18
3.2.10. +5 VDC / +3.3 VDC Power Sequencing ..............................................................18
3.2.11. Voltage Hold-up Time........................................................................................18
3.3. Timing / Housekeeping / Control ......................................................................................18
3.3.1. PWR_OK..........................................................................................................19
3.3.2. PS_ON#............................................................................................................19
3.3.3. +5 VSB .............................................................................................................20
3.3.4. Power-on Time ...................................................................................................21
3.3.5. Risetime............................................................................................................21
3.3.6. Overshoot at Turn-on / Turn-off.............................................................................21
3.3.7. Reset after Shutdown .........................................................................................21
3.3.8. +5 VSB at AC Power-down.................................................................................21
3.4. Output Protection...........................................................................................................22
3.4.1. Over-voltage Protection.......................................................................................22
3.4.2. Short -circuit Protection.......................................................................................22
3.4.3. No-load Operation ..............................................................................................22
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ATX12V Power Supply Design Guide
Version 1.3
3.4.4. Over-current Protection.......................................................................................22
3.4.5. Over-temperature Protection ................................................................................23
3.4.6. Output Bypass...................................................................................................23
4. Mechanical.......................................................................................................................24
4.1. Labeling / Marking..........................................................................................................24
4.2. Physical Dimensions ......................................................................................................24
4.3. Airflow / Fan..................................................................................................................27
4.4. AC Connector ................................................................................................................28
4.5. DC Connectors ..............................................................................................................28
4.5.1. ATX Main Power Connector .................................................................................30
4.5.2. +12 V Power Connector ......................................................................................30
4.5.3. Auxiliary Power Connector for Configurations with +3.3 VDC Output > 18 A or +5 V
Output > 24 A...................................................................................................30
4.5.4. Peripheral Connector(s)......................................................................................31
4.5.5. Serial ATA Power Connector...............................................................................31
4.5.6. Floppy Drive Connector .......................................................................................31
5. Environmental .................................................................................................................33
5.1. Temperature..................................................................................................................33
5.2. Thermal Shock (Shipping) ...............................................................................................33
5.3. Humidity .......................................................................................................................33
5.4. Altitude.........................................................................................................................33
5.5. Mechanical Shock .........................................................................................................33
5.6. Random Vibration ..........................................................................................................34
5.7. Acoustics......................................................................................................................34
6. Electromagnetic Compatibility...................................................................................35
6.1. Emissions.....................................................................................................................35
6.2. Immunity .........................................................................................................................35
6.3. Input Line Current Harmonic Content and Line Flicker........................................................36
6.4. Magnetic Leakage Fields................................................................................................36
7. Reliability..........................................................................................................................36
7.1. Component De-rating......................................................................................................36
8. Safety................................................................................................................................37
8.1. North America...............................................................................................................37
8.2. International...................................................................................................................38
8.3. Proscribed Materials ......................................................................................................38
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ATX12V Power Supply Design Guide
Version 1.3
Figures
Figure 1. Cross loading Graph for 220W configuration......................................................................11
Figure 2. Cross loading Graph for 250W configuration......................................................................12
Figure 3. Cross loading Graph for 300W configuration......................................................................13
Figure 4. Differential Noise Test Setup ...........................................................................................16
Figure 5. Power Supply Timing .....................................................................................................18
Figure 6. PS_ON# Signal Characteristics ......................................................................................20
Figure 7. Power Supply Dimensions for chassis that does not require top venting ..............................25
Figure 8. Power Supply Dimensions for Chassis that require top venting ...........................................26
Figure 9. ATX12V Power Supply Connectors..................................................................................29
Figure 10. Serial ATA connector ....................................................................................................31
Tables
Table 1. AC Input Line Requirements.............................................................................................8
Table 2. DC Output Voltage Regulation..........................................................................................10
Table 3. Typical Power Distribution for a 220 W ATX12V Configuration..............................................11
Table 4. Typical Power Distribution for a 250 W ATX12V Configuration..............................................12
Table 5. Typical Power Distribution for a 300 W ATX12V Configuration..............................................13
Table 6. Minimum Efficiency Vs load .............................................................................................14
Table 7. Loading table for Efficiency measurements ........................................................................14
Table 8. Energy Star Input Power Consumption..............................................................................15
Table 9. DC Output Noise/Ripple...................................................................................................16
Table 10. DC Output Transient Step Sizes.....................................................................................17
Table 11. Output Capacitive Loads ................................................................................................17
Table 12. PWR_OK Signal Characteristics ....................................................................................19
Table 13. PS_ON# Signal Characteristics ......................................................................................20
Table 14. Overvoltage Protection...................................................................................................22
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ATX12V Power Supply Design Guide
Version 1.3
1. Introduction
1.1. Scope
This document provides design suggestions and reference specifications for a family of power
supplies that comply with the ATX Specification, Version 2.03† for motherboards and chassis.
It includes supplementary information not expressly detailed in the ATX Specification, such as
information about the physical form factor of the power supply, cooling requirements, connector
configuration, and pertinent electrical and signal timing specifications.
This document is provided as a convenience only and is not intended to replace the user’s
independent design and validation activity. It should not be inferred that all ATX12V power
supplies must conform exactly to the content of this document. The design specifics described
herein are not intended to support all possible system configurations. System power supply needs
vary widely depending on factors such as the application (that is, for desktop, workstation, or
server), intended ambient environment (temperature, line voltage), or motherboard power
requirements.
1.2. ATX12V as Compared with ATX Power Supply
This section briefly summarizes the major changes made to this document that now defines
ATX12V power supply. With the move to 12V voltage regulators for the CPU, ATX guidelines
for 5V as main power are no longer provided.
1.2.1. Key Changes for ATX12V Version 1.3
Increased +12 VDC output capability. System components that use 12V are continuing to
increase in power. ATX12V power supplies should be designed to accommodate these
increased +12 VDC current.
• Minimum Efficiency: Minimum measured efficiency and full load has been increased to 70%.
Efficiency guidelines have been added for 50% load and 20% load.
• -5V removal: Guidance for –5V has been removed. This legacy voltage was in support of
ISA add-in cards. ISA cards are no longer used for a majority of the industry, but custom
applications my still exist, refer to Version 1.2 for –5V recommendations.
†
2.03 is the current version of the ATX Specification as of this writing. Future references to the ATX
Specification in this document imply version 2.03 or later , as applicable.
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ATX12V Power Supply Design Guide
Version 1.3
2. Applicable Documents
The following documents support this design guide as additional reference material.
Document Title Description
FCC Rules Part 15, Class B Title 47, Code of Federal Regulations, Part 15
ICES-003: 1997, Class B Interference-Causing Equipment Standard – Digital Apparatus
EN 55022: 1998 +
Amendment A1:2000 Class B
CISPR 22: 1997, Class B
AS/NZS 3548:1995, Class B
EN 55024:1998
IEC 60950, 3rd ed., 1999 Safety of Information Technology Equipment
EN 60950: 2000 Safety of Information Technology Equipment
UL 60950, 3rd ed., 2000 Safety of Information Technology Equipment
CSA 22.2 No. 60950-00 Safety of Information Technology Equipme nt
Information Technology Equipment – Radio disturbance characteristics –
Limits and methods of measurement
Information Technology Equipment – Radio disturbance characteristics –
Limits and methods of me asurement
Information Technology Equipment – Radio disturbance characteristics –
Limits and methods of measurement
Information Technology Equipment – Immunity Characteristics – Limits and
methods of measurement
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ATX12V Power Supply Design Guide
Version 1.3
3. Electrical
The electrical requirements that follow are to be met over the environmental ranges specified in
Section 5 unless otherwise noted.
3.1. AC Input
Table 1 lists AC input voltage and frequency requirements for continuous operation. The power
supply shall be capable of supplying full-rated output power over two input voltage ranges rated
100-127 VAC and 200-240 VAC RMS nominal. The correct input range for use in a given
environment may be either switch-selectable or auto-ranging. The power supply shall
automatically recover from AC power loss. The power supply must be able to start up under
peak loading at 90 VAC.
Table 1. AC Input Line Requirements
Parameter Minimum Nominal+ Maximum Unit
Vin (115 VAC) 90 115 135 VAC
Vin (230 VAC) 180 230 265 VAC
Vin Frequency 47 -- 63 Hz
+Note: Nominal voltages for test purposes are considered to be within ±1.0 V of nominal.
3.1.1. Input Over-current Protection
The power supply shall incorporate primary fusing for input over-current protection to prevent
damage to the power supply and meet product safety requirements. Fuses should be slow-blow –
type or equivalent to prevent nuisance trips‡.
3.1.2. Inrush Current Limiting
Maximum inrush current from power-on (with power on at any point on the AC sine) and
including, but not limited to, three line cycles, shall be limited to a level below the surge rating of
the input line cord, AC switch if present, bridge rectifier, fuse, and EMI filter components.
Repetitive ON/OFF cycling of the AC input voltage should not damage the power supply or
cause the input fuse to blow.
rms
rms
‡
. For Denmark and Switzerland international safety requirements, if the internal over -current protective
devices exceed 8A for Denmark and 10A for Switzerland, then the power supply must pass international safety
testing to EN 60950 using a maximum 16A over -current protected branch circuit, and this 16A (time delay fuse)
branch circuit protector must not open during power supply abnormal operation (output short circuit and
component fault) testing.
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ATX12V Power Supply Design Guide
Version 1.3
3.1.3. Input Under-voltage
The power supply shall contain protection circuitry such that the application of an input voltage
below the minimum specified in Section 3.1, Table 1, shall not cause damage to the power supply.
3.1.4. Regulatory
Both system and power supply typically must pass testing per the limits and methods described in
EN 55024 specifications prior to sale in many parts of the world. Additional requirements may
depend on the design, product end use, target geography, customer, and other variables. Consult
your company’s Product Safety and Regulations department for more details.
3.1.5. Catastrophic Failure Protection
Should a component failure occur, the power supply should not exhibit any of the following:
• Flame
• Excessive smoke
• Charred PCB
• Fused PCB conductor
• Startling noise
• Emission of molten material
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ATX12V Power Supply Design Guide
Version 1.3
3.2. DC Output
3.2.1. DC Voltage Regulation
The DC output voltages shall remain within the regulation ranges shown in Table 2 when
measured at the load end of the output connectors under all line, load, and environmental
conditions. The voltage regulation limits shall be maintained under continuous operation for any
steady state temperature and operating conditions specified in Section 5.
Table 2. DC Output Voltage Regulation
Output Range Min. Nom. Max. Unit
+12VDC
+3.3VDC
-12VDC ±10% -10.80 -12.00 -13.20 Volts
(1)
(2)
(1)
±5% +11.40 +12.00 +12.60 Volts
+5VDC ±5% +4.75 +5.00 +5.25 Volts
(2)
±5% +3.14 +3.30 +3.47 Volts
+5VSB ±5% +4.75 +5.00 +5.25 Volts
At +12 VDC peak loading, regulation at the +12 VDC output can go to ± 10%.
Voltage tolerance is required at main connector and S-ATA connector (if used).
3.2.2. Remote Sensing
The +3.3 VDC output should have provisions for remote sensing to compensate for excessive
cable drops. The default sense should be connected to pin 11 of the main power connector. The
power supply should draw no more than 10 mA through the remote sense line to keep DC offset
voltages to a minimum.
3.2.3. Typical Power Distribution
DC output power requirements and distributions will vary based on specific system options and
implementation. Significant dependencies include the quantity and types of processors, memory,
add-in card slots, and peripheral bays, as well as support for advanced graphics or other features.
It is ultimately the responsibility of the designer to derive a power budget for a given target
product and market.
Table 3 through Table 5 and Figure 1 through Figure 3 provide sample power distributions and a
graphical recommendation for cross loading. It should not be inferred that all power supplies must
conform to these tables, nor that a power supply designed to meet the information in the tables
will work in all system configurations.
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ATX12V Power Supply Design Guide
Version 1.3
3.2.3.1. ATX12V Configurations
Table 3. Typical Power Distribution for a 220 W ATX12V Configuration
Min.
Current
Output
+12 VDC 1.0 14.0 16.0
+5 VDC 0.3 18.0
+3.3 VDC 0.5 14.0
-12 VDC 0.0 0.5
+5 VSB 0.0 2.0 2.5
Note: Total combined output of 3.3 V and 5 V is < 110W
Peak currents may last up to 17 seconds with not more than one occurrence per minute
(amps)
Max.
Current
(amps)
Peak
Current
(amps)
Figure 1. Cross loading Graph for 220W configuration
220W Cross Regulation
(5V rail + 3.3V rail vs. 12V)
120
100
80
60
40
20
3.3V + 5V power (watts)
0
0 50 100 150 200
12V power (watts)
Combined Power
(5V rail + 3.3V rail)
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ATX12V Power Supply Design Guide
Version 1.3
Table 4. Typical Power Distribution for a 250 W ATX12V Configuration
Min.
Current
Output
+12 VDC 1.0 17.0 19.0
+5 VDC 0.3 21.0
+3.3 VDC 0.5 20.0
-12 VDC 0.0 0.8
+5 VSB 0.0 2.0 2.5
Note: Total combined output of 3.3 V and 5 V is < 140 W
Peak currents may last up to 17 seconds with not more than one occurrence per minute
(amps)
Max.
Current
(amps)
Peak
Current
(amps)
Figure 2. Cross loading Graph for 250W configuration
250W Cross Regulation
(5V rail + 3.3V rail vs. 12V)
160
140
120
100
Combined Power
80
(5V rail + 3.3V rail)
60
40
5V + 3.3V power (watts)
20
0
0 50 100 150 200 250
12V power (watts)
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