Is there a practical difference b/w an axial SMD inductor and coil-style one - Page 1
Forum section: electronics / beginners

author: WarFreak131
author_rank: Contributor
timestamp: July 27, 2020, 09:24:10 pm
content: I am looking to have my first SMD board fabricated. I am making a SEPIC regulator, and one of the things standing in my way is the choice of inductor.Is there any practical difference between the typical axial SMD (like you might see with an SMD resistor/capacitor)https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fae01.alicdn.com%2Fkf%2FHTB1pwQPSFXXXXXHXVXXq6xXFXXX8%2F100pcs-SMD-Inductor-0402-0603-0805-1206-SMD-Inductor-Chip-Inductors-Free-Shipping.jpg&f=1&nofb=1and the coil-style ones?https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fae01.alicdn.com%2Fkf%2FUTB8gjJLXrnJXKJkSahGq6xhzFXak%2FUXCELL-10-Pcs-0-28Ohm-0-85A-10-Smd-Coil-Inductors-Cd75-68Uh-7-8Mmx7mmx5mm.jpg&f=1&nofb=1Thanks

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 28, 2020, 03:18:32 am
content: Well obviously, neither is 4-terminal (dual winding), so you won't get the coupling advantage of SEPIC, just the fully-variable voltage range. (Probably doesn't make any bit of difference on a small thing, using parts like pictured, versus a dual winding part.)FWIW, I'd call those "chip", and "bobbin" or "spool" styles.The chips are smaller, and generally keep the field better contained. They may be listed as shielded or not. How they are wound, and how the external field looks, is inscrutable; you'd have to test (or perhaps find a mfg drawing showing how they're built, axial wound or multilayer stacked perhaps; the latter will probably be better shielded).The bobbin types very obviously aren't shielded, though sometimes they try and say so anyway. Some are such a low profile that they aren't bad at all, but the ones pictured are certainly tall enough that you can, for example, place wires very close to the winding, enough to get useful induced voltages.The kind that looks like a bobbin dropped into a bathtub, those are usually better shielded. Also powder composite types, the body looks like a homogeneous, silvery or gray mass.The inductance, resistance or current rating, and saturation current, are the most important parameters.If you don't have anything terribly nearby the inductors (besides themselves, and other power components), shielding doesn't really matter. Observe normal layout best-practices for switching supplies and sensitive circuitry and signals.Tim

author: vk6zgo
author_rank: Super Contributor
timestamp: July 28, 2020, 12:12:39 pm
content: The Q of the toroid type ones is fairly certain to be better.

author: David Hess
author_rank: Super Contributor
timestamp: July 28, 2020, 04:31:45 pm
content: Quote from: WarFreak131 on July 27, 2020, 09:24:10 pmI call those radial.There definitely are self shielded radial inductors for power applications which enclose the winding inside the core sections like a pot core.

author: WarFreak131
author_rank: Contributor
timestamp: July 28, 2020, 11:40:38 pm
content: Quote from: T3sl4co1l on July 28, 2020, 03:18:32 amThank you for the detailed response. Can you go into a bit more detail regarding what you mean by the coupling advantage?Thanks

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 29, 2020, 12:28:17 am
content: https://www.digikey.com/en/articles/comparing-coupled-and-uncoupled-inductor-sepic-voltage-convertershttps://www.we-online.com/web/en/electronic_components/news_pbs/blog_pbcm/blog_detail-worldofelectronics_77630.phpTim

author: MathWizard
author_rank: Super Contributor
timestamp: July 29, 2020, 08:06:27 am
content: Is there anything like the core material of the coil/radial type, inside the little axial type ?If the Q factor is a measure of the energy the inductor can give back to the system, they'd want the higher Q type which I'd assume is the coil type with the big core. IDK about the power ratings and thermal differences, aside from the size/mass differences.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 29, 2020, 08:43:29 am
content: Core material, certainly; most use ferrite.Tim