Are Normal Jellybean Resistors NTC or PTC? - Page 1
Forum section: electronics / beginners

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 22, 2017, 04:31:04 pm
content: are metal film resistor NTC or PTC?resistor like thishttp://www.ebay.com.my/itm/New-Metal-Film-Resistor-1-2W-0-5W-1-Tolerance-0-1-Ohm-to-910-Ohm-/222468134823?var=&hash=item33cc2257a7:m:m1e2lS_6S6_mdCfYTil3d9ware carbon film resistor NTC or PTC?resistor like thishttp://www.ebay.com.my/itm/0-1R-270R-2W-Watt-Carbon-Film-Resistors-5-0-1-to-750-Ohm-Free-P-P-Kits-/222359157874?var=&hash=item33c5a37c72:m:mEZ0D56w3n40wiKx1FI8aRA

author: Audioguru
author_rank: Super Contributor
timestamp: April 22, 2017, 04:34:49 pm
content: Ordinary resistors are made so that their value does not change when the temperature changes. Cheap resistors made "over there" might change their value a little with temperature changes.I cannot remember if too much rice in a resistor causes it to be NTC or PTC.

author: Zero999
author_rank: Super Contributor
timestamp: April 22, 2017, 04:41:16 pm
content: Quote from: Mechatrommer on April 22, 2017, 04:31:04 pmCarbon resistors are likely to NTC because carbon is a semiconductor and its resistance decreases, with increasing temperature. Metal film resistors are more likely to be PTC, since the resistance of all metals increases with increasing temperature.However in practise the above could be incorrect, since resistors are quite likely to be made from mixtures of different materials, with cancelling temperature coefficients. I suspect, whether it's PTC or NTC depends on the type of resistor and its value, with there being a certain sweet-value, with the lowest temperature coefficient.Note: I haven't done any research into this. Check the datasheet, for more information.

author: Nerull
author_rank: Frequent Contributor
timestamp: April 22, 2017, 05:32:57 pm
content: Quote from: Audioguru on April 22, 2017, 04:34:49 pmI take it you've never actually checked.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 22, 2017, 05:39:56 pm
content: Quote from: Nerull on April 22, 2017, 05:32:57 pmIt depends on why we are having this discussion. In virtually all cases, we take for granted that a resistor should live within its specified tolerance (10%, 5%, 2%, 1%, etc.) over the "normal" (0~100°C?) temperature range.Circuits that need to be particularly stable and/or operate over a wider temperature range should be designed for that purpose and not rely on "jelly-bean" components and specs. Otherwise, the question seems rather "goofy" to me.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 22, 2017, 06:06:24 pm
content: i was going to use the 2W 0.1ohm carbon film resistor as load balancing in parallel mosfets working in linear region (emitter follower, or "source" follower). but after reading the net and here, the weight is more heavy on the answer that the jelly-bean resistor is a NTC, so its not suitable for the job. hence i ditch out the idea of load balancing and just connect the mosfets source pin together. thanks all guys for your reply.

author: Monkeh
author_rank: Super Contributor
timestamp: April 22, 2017, 06:30:42 pm
content: Quote from: Mechatrommer on April 22, 2017, 06:06:24 pmCarbon will be NTC, metal will be PTC.

author: wraper
author_rank: Unknown
timestamp: April 22, 2017, 06:47:14 pm
content: Quote from: Monkeh on April 22, 2017, 06:30:42 pmThey won't. First of all tempco is usually specified as +/-, like +-100ppm/C. Tempco is not linear and depending on temperature and can even change from positive to negative. Not to say you can get mostly positive or negative tempco depending on type, value, particular batch, particular resistor.

author: Monkeh
author_rank: Super Contributor
timestamp: April 22, 2017, 06:49:47 pm
content: Quote from: wraper on April 22, 2017, 06:47:14 pmInteresting, fair point. It's an alloy in film resistors, so it will vary.My experience is power resistors (usually wirewound) are positive whenever I've looked, at any rate.

author: wraper
author_rank: Unknown
timestamp: April 22, 2017, 06:54:42 pm
content: Quote from: Monkeh on April 22, 2017, 06:49:47 pmIt's not just an alloy. In the case of thick film resistors, it's a composite consisting of metal alloy powder and insulating particles mixed together, applied on the substrate and then baked.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 22, 2017, 07:07:38 pm
content: Carbon resistors are usually NTC.With metal film resitors it depends, they can have both a positive or negative TC. One can even have resistors from the same type one with positive and one with negative TC. The cheap one are usually -100 ... +100 ppm/K.There are a some low ohms power resitors with PTC behaviour in all cases (e.g. +100-500 ppm/K) - they are especially useful for load sharing.I doubt you get 0.1 Ohms as carbon film. Resistors in this range are usually wire type.

author: Audioguru
author_rank: Super Contributor
timestamp: April 22, 2017, 11:24:11 pm
content: The resistors are cheap ones from China. The manufacturer is unknown so there is no datasheet.I would never buy cheap resistors with no datasheet from ebay.

author: amspire
author_rank: Super Contributor
timestamp: April 23, 2017, 02:15:47 am
content: I did a test years ago of about 100 metal film resistors (3k9 1W I think from memory) from a batch from one supplier and found the coefficients all over the place within the +/- 50ppm spec. The majority were NTC. I was hoping the coefficients would be similar and they were not. There were some PTC, some NTC and some that went from PTC to NTC over a 0 deg C to 50 deg C range.I was also hoping that they would be much better then 50ppm/C, but a handful would have made a 20ppm/C spec. When they say +/- 50ppm/C, they mean +/- 50ppm/C. I seem to remember that most were worse then +/- 40ppm/C.

author: SeanB
author_rank: Super Contributor
timestamp: April 23, 2017, 11:06:04 am
content: That was likely because the better parts were selected out from there, leaving the outliers as your parts.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 23, 2017, 12:24:19 pm
content: really? or none at all? who cares selecting 1 cent part produced in millions? or how it even possible to do it in timely economically?