Intel ATX12V manual Output Protection, Over-voltage Protection, Short-circuit Protection

ATX12V Power Supply Design Guide

Version 2.0

3.4. Output Protection

3.4.1. Over-voltage Protection

The over-voltage sense circuitry and reference shall reside in packages that are separate and distinct from the regulator control circuitry and reference. No single point fault shall be able to cause a sustained over-voltage condition on any or all outputs. The supply shall provide latch-mode over-voltage protection as defined in Table 15.

Table 15. Overvoltage Protection

Output	Min.	Nom.	Max.	Unit
+12 V1DC & +12V2DC	13.4	15.0	15.6	Volts
+5 VDC	5.74	6.3	7.0	Volts
+3.3 VDC	3.76	4.2	4.3	Volts

3.4.2. Short-circuit Protection

An output short circuit is defined as any output impedance of less than 0.1 ohms. The power supply shall shut down and latch off for shorting the +3.3 VDC, +5 VDC, or

+12 VDC rails to return or any other rail. The +12 V1DC and +12V2DC should have separate short circuit and overload protection. Shorts between main output rails and +5 VSB shall not cause any damage to the power supply. The power supply shall either shut down and latch off or fold back for shorting the negative rails. +5 VSB must be capable of being shorted indefinitely, but when the short is removed, the power supply shall recover automatically or by cycling PS_ON#. The power supply shall be capable of withstanding a continuous short-circuit to the output without damage or overstress to the unit (for example, to components, PCB traces, connectors) under the input conditions specified in Section 3.1. The maximum short-circuit energy in any output shall not exceed 240 VA, per IEC 60950 requirements.

3.4.3. No-load Operation

No damage or hazardous condition should occur with all the DC output connectors disconnected from the load. The power supply may latch into the shutdown state.

3.4.4. Over-current Protection

Overload currents applied to each tested output rail will cause the output to trip before reaching or exceeding 240 VA. For testing purposes, the overload currents should be ramped at a minimum rate of 10 A/s starting from full load.

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