Power Supply Leakage Current When No Load Is Applied

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Discussion Overview

The discussion revolves around the current drawn by a power supply when no load is applied, specifically focusing on the interpretation of leakage current mentioned in datasheets and the actual current consumption of different types of power supplies.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the leakage current mentioned in the datasheet refers to the current drawn when no load is applied, suggesting it is on the order of microamps.
  • Another participant clarifies that the current drawn from the mains by a bench-top power supply is likely not in the microamp range due to additional circuitry and losses, and suggests measuring it with a clamp-style ammeter.
  • A different participant specifies they are referring to a dual output linear open chassis power supply, which may differ from more complex laboratory power supplies.
  • One participant explains that the leakage current referred to in safety regulations is related to leakage to Earth Ground, highlighting its significance for safety, especially in medical devices.
  • There is mention that the no-output-load input power consumption may sometimes be specified for power supplies, particularly for components like linear voltage regulators.
  • A suggestion is made to measure the current using an AC current clamp and to separate the Hot/Neutral wires carefully for accurate measurement.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the current drawn by various types of power supplies and the interpretation of leakage current, indicating that multiple competing views remain without a consensus.

Contextual Notes

There are limitations regarding the definitions of leakage current and the specific types of power supplies discussed, as well as the potential variability in specifications provided by manufacturers.

cepheid
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If I want to find out the current drawn by a power supply when no load is placed on it. It isn't obvious what this is in the datasheet, but under Safety, Regulartory, and EMI regulations, it does mention a leakage current on the order of microamps. Would that be it, or does that refer to something else?
 
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You mean, the current drawn from the mains by a bench-top power supply? It won't be microamps. A precision power supply has a lot of control circuitry, display circuitry, etc. -- not to mention losses. You could measure it fairly easily with a clamp-style ammeter, but I don't know how common it is for power supply manufacturers to put this kind of info in their manuals.

- Warren
 
Hmm ok. No I was not talking about a laboratory power supply, but one of those dual output (5 V, 12 V) linear open chassis power supplies that just basically has a transformer on one side and some sort of circuit board on the other side, that, through magic (regulators etc) produces the DC outputs. Anyway, don't worry about it.
 
I believe the leakage current you are referring to ("safety" related) is the leakage current to Earth Ground. This is a safety/health concern because of the shock hazard. Depending on the input EMI filter configuration, you can end up with more leakage current to Ground than is permitted, especially for medical devices.

The no-output-load input power consumption will sometimes be specified for a power supply. It certainly is for power supply components, like linear voltage regulators, for example. If you need to measure it, get an AC current clamp from the electronics store (about $50) that you plug into your DVM. Then separate the Hot/Neutral wires in the supply cord somehow (carefully), and clamp the measuring device over either wire.
 

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