Hardware Reference
24
Power supply
Q35 motherboards support soft-switched and hard-switched ATX power supplies. The standard
24-pin ATX power connector provides +12V, -12V, +5V standby, +5V, +3.3V power rails and an
extra 4-pin ATX power connector provides +12V for CPU use only.
A 20-pin ATX power connector can also be used. In this case, plug the 20-pin cable in on the
pin #1 side of the connector and leave the two pairs of pins on the other side exposed. No
adaptor is required.
W
ARNING! The power supply must be approved by a third-party agency for use in IEC/EN/UL/
CSA 60950 applications.
Voltage requirements
Table 19 shows the maximum load currents on all ATX power rails. Ensure that the power
supply can support the required load current on all rails, otherwise, it can cause damage to the
power supply or the motherboard.
A 5V standby power rail is optional, but if not provided, the soft-switched power supply control
features of the motherboard cannot be used. When there is a standby rail, make sure it can
provide sufficient current for the motherboard, taking into account the Ethernet controllers and
any adapter card that draws current from the auxiliary 3.3V supply. The ATX -5.0V rail is not used
by the Q35 motherboards.
Table 19. Maximum load currents on ATX power rails
Power Rail Maximum Load Current
+12V 12A
-12V 0.1A
+5V 18.75A
+3.3V 6.72A
+5V standby 1.25A
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