Author Topic: Component label NTC1 ?  (Read 8862 times)

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Offline JebnorTopic starter

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Component label NTC1 ?
« on: July 26, 2013, 01:04:28 am »
I'm exploring an old Switch mode power supply which died.  There is an unpopulated area "NTC1", Two pin and on the same trace, directly from mains.  What could it be used for?  any ideas?
Before this, there was a typo.
 

Offline dfmischler

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Re: Component label NTC1 ?
« Reply #1 on: July 26, 2013, 01:08:50 am »
Negative Temperature Coefficient?  Cut the trace and put in the resistor and it limits inrush current at startup, then reduces its resistance once warmed up?  Or something like that?  Since we haven't been shown the circuit this is totally guesswork...
 

Offline IanB

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Re: Component label NTC1 ?
« Reply #2 on: July 26, 2013, 01:10:08 am »
What does "on the same trace" mean? I don't know how to read that.

As to NTC1 it could mean an NTC thermistor (negative temperature coefficient), used for inrush limiting. Otherwise the capacitors on the input side of the supply will provide an effective short circuit across the mains when first powered up.
 

Offline c4757p

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Re: Component label NTC1 ?
« Reply #3 on: July 26, 2013, 01:15:53 am »
What does "on the same trace" mean? I don't know how to read that.

They bypassed the thermistor with a trace because they chose not to populate it, so both pads are joined.

And I agree. 99.99% certain it's an inrush-limiting thermistor.
« Last Edit: July 26, 2013, 01:25:28 am by c4757p »
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Offline JebnorTopic starter

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Re: Component label NTC1 ?
« Reply #4 on: July 26, 2013, 01:30:41 am »
Negative Temperature Coefficient?  ... Since we haven't been shown the circuit this is totally guesswork...
The circuit is not dissimilar from the typical application of the AP3101


What does "on the same trace" mean? I don't know how to read that.

They bypassed the thermistor with a trace because they chose not to populate it, so both pads are joined.
I think that is it.  A bypassed Thermistor.
Before this, there was a typo.
 


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