Inductors - Page 1
Forum section: electronics / beginners

author: 00
author_rank: Contributor
timestamp: July 26, 2020, 08:06:58 pm
content: I wonder why do variable inductors have 5 pins. I found one or two schematics but still can't get it. Can someone please explain?

author: madires
author_rank: Super Contributor
timestamp: July 26, 2020, 08:27:18 pm
content: Are you talking about IF transformers?

author: 00
author_rank: Contributor
timestamp: July 26, 2020, 08:36:51 pm
content: I don't think so. I'm talking about those that don't have case and you can see wires.

author: madires
author_rank: Super Contributor
timestamp: July 26, 2020, 08:39:50 pm
content: A picture would be helpful.

author: 00
author_rank: Contributor
timestamp: July 26, 2020, 08:57:39 pm
content: Something like this.

author: madires
author_rank: Super Contributor
timestamp: July 26, 2020, 09:04:37 pm
content: Is that a single coil or a transformer?

author: 00
author_rank: Contributor
timestamp: July 26, 2020, 09:11:24 pm
content: I don't know. It has 3 pins on one side 2 on the other. Wires are connected on all 3 pins on one side and to one on the other. If I google variable/adjustable inductor I get some images like this.

author: Vovk_Z
author_rank: Super Contributor
timestamp: July 26, 2020, 09:16:50 pm
content: It seems to me reasonable that it may need more than two pins because it has more than one winding.

author: madires
author_rank: Super Contributor
timestamp: July 26, 2020, 09:20:09 pm
content: Check the windings with a DMM by measuring the resistance between the pins. If it has two isolated coils then it's a transformer.

author: 00
author_rank: Contributor
timestamp: July 26, 2020, 09:32:15 pm
content: One pin(on the side with 2 pins) is connected to all 3 pins on the other side but the second pin(on the side with 2 pins) isn't connected anywhere

author: Buriedcode
author_rank: Super Contributor
timestamp: July 27, 2020, 05:18:20 am
content: Perhaps its just a generic former that has 5 pins? I can't say I've seen one exactly like that, but plenty of vertical inductors I've seen in CRT's and TV's have a based with more than two pins, but it only has connections to two.

author: chris_leyson
author_rank: Super Contributor
timestamp: July 27, 2020, 05:33:52 am
content: Mechanical stability perhaps.

author: Circlotron
author_rank: Super Contributor
timestamp: July 27, 2020, 06:47:57 am
content: 5 pins to allow insertion into a board only one way?

author: madires
author_rank: Super Contributor
timestamp: July 27, 2020, 09:35:31 am
content: Yep, additional unwired pins are used for mounting. But this one has four pins wired to a coil with multiple taps.

author: Zero999
author_rank: Super Contributor
timestamp: July 27, 2020, 10:20:44 am
content: Quote from: Buriedcode on July 27, 2020, 05:18:20 amYes, I've seen those in RF equipment ranging from TVs and radios to remote controls. It's a generic former for use as an inductor or transformer. A ferrite core is often screwed in the middle and can be adjusted, but often it's left out making it an air core. I suspect they're used over the 10MHz to 100MHz frequency range.

author: David Hess
author_rank: Super Contributor
timestamp: July 27, 2020, 05:45:17 pm
content: Quote from: Circlotron on July 27, 2020, 06:47:57 amExactly, they use a common coil mounting for transformers and inductors and an asymmetrical pin arrangement prevents insertion backwards.