# How can I measure Quiescent current of LDO's?

Discussion in 'General Electronics Discussion' started by dhlee, Oct 20, 2014.

1. ### dhlee

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Aug 27, 2014
I thought one, make sure the load is infinite.
Is this available?

2. ### Harald KappModeratorModerator

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Nov 17, 2011
Infinite load = no load at all or short circuit, depends on what you understand when you say infinite (infinite resistance or infinite current)
In you case, quiescent current is measured at the input of the LDO with no load attached.

3. ### KrisBlueNZSadly passed away in 2015

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Nov 28, 2011
The quiescent current in a regulator is the current that flows into the input, but not out the output. Therefore it must flow through the ground connection. It is also called the "ground current". So, measure the current flowing through the ground lead.

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4. ### hevans1944Hop - AC8NS

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Jun 21, 2012
Kirchoff's Law in action: What goes into a node must also go out of the node.

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5. ### hevans1944Hop - AC8NS

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Jun 21, 2012
For Kirchoff's Law, a node is any bounded region, not just a point where two or more conductors are connected. In this case the entire 3-terminal regulator with input, output, and ground is considered a node. The Law quite simply states that all the current entering a bounded region (a node) must be equal to all the current leaving the bounded region. It doesn't matter what kind of circuitry is inside the region!

Why is this so? Because otherwise there would be an accumulation of charge, either positive or negative, from the excess of current entering or the excess of current leaving the region. You think a Van de Graaf generator is a counter-example to Kirchoff's Law? Think again. All those charges (current) being carried on the belt to the top of the generator eventually come back down when current is drawn from the charged sphere at the top.

Kirchoff's Law is used together with Ohm's Law to analyze circuits. No matter how many parallel and series connected components you have, application of these two laws will allow you determine the voltage drop across and current through each component.

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