Hold-up time (bridging time)
Hold-up time is a bridging time that describes the period during which the specified output power continues to be provided in the event of an input voltage failure. Even normal power supply units can bridge short-term power failures of up to a few seconds using appropriately dimensioned input storage electrolytic capacitors. The hold-up time here is really long and therefore good.
Timings
Desktop PSU timings refer to the specific timing and signal sequences that a power supply must adhere to according to the ATX specification to ensure proper operation of a computer system. Correct timings are critical to system stability as they prevent crashes or damage by ensuring that all components receive a consistent and timely power supply.
In desktop power supply units (PSUs), the so-called Alternative Low Power Modes (ALPM), as defined in the ATX specification (e.g. ATX v3.1), serve to improve energy efficiency. They reduce power consumption at low loads or when idle, for example when a computer is in sleep or standby mode. These operating modes are closely related to the T1 and T3 timings, which are crucial for ensuring that the power supply responds correctly during transitions between different power states.
The power supply supports the Alternative Low Power Modes.
- T1 (Power-On Time): This is the time from when the PSU is turned on (via the PS_ON# signal going low) to when the output voltages are stable and within specification, and the Power Good (PWR_OK) signal is asserted. Typically, T1 is less than 500 ms, but it must be below 200 ms for ALPM compliance, and Intel recommends a value of below 150 ms. It ensures the system receives stable power quickly during startup or when waking from a low-power state.
- T3 (Power Good Delay): The time interval between when the output voltages reach their nominal levels and when the PWR_OK signal is asserted, typically 100-500 ms. For ALPM compliance, it must be between 100 and 250 ms, with Intel recommending 100-150 ms. T3 ensures the PSU signals the system only when the power output is fully stable.
Inrush current (starting current or inrush current)
All power supply units generate a so-called inrush current, which often far exceeds their nominal current consumption. The causes are the charging of the different capacitances in the input circuit and in the EMC filters, the build-up of the magnetic field in the transformer core and even the charging of the capacitors in the output filter. This input current only drops back to normal values when the converter is operating stably. The inrush currents are extremely low, so that no meaningful measured values could be recorded.
Leakage current
Leakage current refers to the small current that flows through an insulating material or a semiconductor component, even though it should ideally be non-conductive. It typically occurs in electronic components such as transistors, capacitors and insulators when current flows through material defects or unintended conductive paths, even when the component is “switched off”. In power supplies, the leakage current is an alternating current that flows via the protective conductor. The main cause of this is the Y capacitors (Cy) of the EMC filter. The more Y capacitors there are, the higher the leakage current can be. The IEC 62368-1 standard, which replaces the earlier IEC 60950 (office equipment) and IEC 60065 (consumer and electronic equipment) standards, specifies the limit values for the maximum permissible leakage or touch current:
– Normal operating condition: maximum touch current = 3.5 mA
– Single fault condition: maximum touch current = 10 mA
The measured values are very low:
- 1 - Introduction, Prices and Technical Data
- 2 - Unboxing, Cables and iCUE
- 3 - Protection and EMI
- 4 - Teardown: Topology, components and craftmanship
- 5 - Load Regulation, Ripple Suppression, Transient Resonse
- 6 - Hold-Up Time, Timings, Inrush-Current
- 7 - Average Efficiency and PF
- 8 - Operating noise and fan
- 9 - Summary and conclusion
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