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How We Test Power Supply Units

Inrush Current

Inrush current, or switch-on surge, refers to the maximum, instantaneous input current drawn by an electrical device when it is first turned on. Because of the charging current of the APFC capacitor(s), PSUs produce significant inrush current as soon as they are turned on. A large enough inrush current can cause the tripping of circuit breakers and fuses, and may also damage switches, relays and bridge rectifiers. As a result, the lower the inrush current of a PSU right as it is turned on, the better.

We also noticed that the lower the input voltage, the lower the inrush current. Thus, when operating with 115 VAC, a PSU has much smaller inrush current compared with 230 VAC input. Both our Chroma AC source and the Yokogawa power analyzer have the ability to measure inrush current.

Aris Mpitziopoulos
Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.