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ATX12V Power Supply Design Guide
Version 2.0
9
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
V
in
(115 VAC) 90 115 135 VAC
rms
V
in
(230 VAC) 180 230 265 VAC
rms
V
in
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.
‡
. 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.