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No load current drawn

by cepheid
Tags: current, drawn, load
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cepheid
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Jun4-07, 02:06 PM
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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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chroot
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Jun4-07, 02:12 PM
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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.

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cepheid
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Jun4-07, 02:31 PM
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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.

berkeman
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Jun4-07, 03:44 PM
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No load current drawn

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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