ATX12V Power Supply Design Guide
Version 2.0
3.3.1. PWR_OK
PWR_OK is a “power good” signal. It should be asserted high by the power supply to indicate that the +12 VDC, +5VDC, and +3.3VDC outputs are above the
Table 13. PWR_OK Signal Characteristics
Signal Type
Logic level low
Logic level high
PWR_OK delay
PWR_OK risetime
AC loss to PWR_OK
+5 V TTL compatible
< 0.4 V while sinking 4 mA
Between 2.4 V and 5 V output while sourcing 200 µA
1 kΩ from output to common
100 ms < T3 < 500 ms
T4 ≤ 10 ms
T5 ≥ 16 ms
T6 ≥ 1 ms
3.3.2. PS_ON#
PS_ON# is an
The power supply shall provide an internal
The power supply shall 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.
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