Question about the values of inductor coils.  - Page 1
Forum section: electronics / beginners

author: mkvl
author_rank: Contributor
timestamp: June 10, 2023, 05:24:24 pm
content: I would like to know if this two inductor coils in the picture have the same value? Or if it should be has the same value?.Thank you.

author: CountChocula
author_rank: Unknown
timestamp: June 10, 2023, 06:15:47 pm
content: Not necessarily—it depends on the application. The number of windings could be the same if all you care is line isolation, or it could be significantly different if you need to convert from high to low impedance to drive your speakers (this used to be a particular issue with valves, as I understand). Like with so many other things that have to with amplifiers, Rod Elliott has agreat articleon the subject (if you aren't familiar with his site, it's a great resource).

author: RoGeorge
author_rank: Super Contributor
timestamp: June 10, 2023, 06:22:56 pm
content: A 1:1 transformer (which will imply same value for coils) is more an exception than the norm, so no, usually they are not the same value.About the posted schematic, it should say somewhere in the description how many turns has to be in each coil, and their physical dimension (length/diameter/core type, etc).

author: TimFox
author_rank: Super Contributor
timestamp: June 10, 2023, 06:47:26 pm
content: For RF tuned circuits, the self-inductance of each coil may differ, but the mutual inductance may well be less than the value for unity coupling.These parameters are used to effect impedance matching in narrowband circuits.

author: MathWizard
author_rank: Super Contributor
timestamp: June 10, 2023, 09:03:47 pm
content: Do you have any circuit simulator like LTSpice ? There's also more graphically oriented circuit simulators, that show the flow of currents.I should try 1 of them also, on some SMPS gate drive circuits I'm trying to understand. I'm about to desolder some SMD parts, to really find out what they are, because it doesn't work right in LTSpice. Trying to identify sot23 SMD transistors and diodes is hard sometimes.

author: TimFox
author_rank: Super Contributor
timestamp: June 10, 2023, 09:33:13 pm
content: In Spice itself, the syntax for two (linear) inductors L1 and L2 coupled to each other isL1 20 21 <value>L2 30 31 <value>K12 L1 L2 <value>where L1 and L2 are self-inductances (note that in each case the first node listed is the + terminal, to define polarity of the coupling)and the coupling co-efficient K12 is defined byK12=M12/ (L1L2)1/2< 1whereM12is the mutual inductance between the two inductors (polarity sensitive).

author: AK6DN
author_rank: Regular Contributor
timestamp: June 10, 2023, 09:39:21 pm
content: Quote from: mkvl on June 10, 2023, 05:24:24 pmThat is not really two inductor coils, as in separate inductors. It is physically a transformer. which is built using two physically interleaved inductors as a single assembly.The turns ratio can be 1:1, or whatever your circuit requires. The nominal inductance of the winding(s) is also variable, depending on the application (ie, audio vs radio frequencies).So I think you misunderstand what that graphics symbol in the schematic implies.

author: radiolistener
author_rank: Super Contributor
timestamp: June 10, 2023, 09:55:39 pm
content: this transformer can be 1:1 or whatever you want. It depends on your load impedance.

author: TimFox
author_rank: Super Contributor
timestamp: June 10, 2023, 10:32:27 pm
content: Quote from: AK6DN on June 10, 2023, 09:39:21 pmThat graphic symbol is not as specific as you state. It could be two inductors that do not overlap but are wound on the same coil form.It suggests a 1:1 turns ratio, but that is just sloppy use of a template.A careful drawing would show the polarity with heavy black dots at one end of each coil.

author: Circlotron
author_rank: Super Contributor
timestamp: June 10, 2023, 11:31:07 pm
content: In that circuit the primary side inductance will be whatever is needed to resonate with the capacitor connected across it. The secondary side can have less turns so it can feed a lower voltage higher current into a low impedance, or more turns so it can feed a higher voltage lower current into a high impedance. Or anything in between.

author: mkvl
author_rank: Contributor
timestamp: June 10, 2023, 11:31:33 pm
content: I know that's a transformer symbol, I just used the term inductor.Thank you.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 10, 2023, 11:58:34 pm
content: Quote from: TimFox on June 10, 2023, 10:32:27 pmThe labelling "output" implies a transformer.Unless the phase in each winding is important, there is little need for "black dots".As the circuit purports to be "basic tuned", they could have dispensed with the secondary winding.Transformer coupling is common, but other techniquesareused-----some RF circuits may be RC coupled, or there may be additional LC coupling circuitry other than the collector tuned circuit.

author: radiolistener
author_rank: Super Contributor
timestamp: June 11, 2023, 12:17:51 am
content: if you want to know which impedance ratio to select for transformer, you can use 1:1 transformer and measure it's output impedance. Then measure your load impedance. Then divide one impedance with another and you will get which impedance ratio is best suitable for your needs.