John Larkin's LC oscillator
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From: Tim Williams on 14 Jun 2010 13:31 "George Herold" <gherold(a)teachspin.com> wrote in message news:bef75813-b0ee-4178-b630-1db31fa97c2c(a)w31g2000yqb.googlegroups.com... > B = u0*N*I*(1/(L1+L2/u)) So if L1 is much greater than L2/u, then the > gap determines the field. (u is the permeability of the material) And > you can also solve for the energy density in the material and in the > gap. And from that calculate the inductance. For which I get, (A is > the area of the material and gap) > > L = u0 *A*N^2*I^2*(1/(L1+L2/u)) > > And the energy stored in the gap is proportional to L1 and that in the > magnetic material to L2/u! Ah yes, I recently did that. Except, L = Phi/I (compare: C = Q/V), so you forgot to cancel the I somewhere. I wrote about it and more here: http://webpages.charter.net/dawill/tmoranwms/Elec_Magnetics.html Should be useful to lots of people who, like you, never got instruction in what the hell a real transformer or inductor is, or how to design one. > Say it seems like toriods are the perfect topology for inductors, do > they make toriods with a built in air gaps? (It doesn't have to be > air.) Well, mix 61 and 67 ferrites have low permeability. I'm not sure if that's due to fillers or magnetic properties. The B-H curve shows a rather wide hysteresis loop (about 7 Oe across), suggesting disturbingly high losses. I don't think powdered irons are even that high, though they lose energy through eddy current as much as hysteresis. Powdered irons could be said to have built in air gaps, since they're usually made from a fine powder (like carbonyl iron, which is spheroidial), compacted and bonded with a resin. The metal density might be 70-90%, I suppose, which is a lot of airgap. Actually, I suppose density would have to be at least 97% for most types, as there are powdered irons with mu_r >= 75 (and I think I saw MPPs as high as 750, but those might be sintered, I'm not sure). Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: George Herold on 14 Jun 2010 14:05 On Jun 14, 1:31 pm, "Tim Williams" <tmoran...(a)charter.net> wrote: > "George Herold" <gher...(a)teachspin.com> wrote in message > > news:bef75813-b0ee-4178-b630-1db31fa97c2c(a)w31g2000yqb.googlegroups.com... > > > B = u0*N*I*(1/(L1+L2/u)) So if L1 is much greater than L2/u, then the > > gap determines the field. (u is the permeability of the material) And > > you can also solve for the energy density in the material and in the > > gap. And from that calculate the inductance. For which I get, (A is > > the area of the material and gap) > > > L = u0 *A*N^2*I^2*(1/(L1+L2/u)) > > > And the energy stored in the gap is proportional to L1 and that in the > > magnetic material to L2/u! > > Ah yes, I recently did that. Except, L = Phi/I (compare: C = Q/V), so you > forgot to cancel the I somewhere. Opps quite right. I set the total energy equal to 1/2L I^2 and forgot to take out the I^2 from both sides... Thanks, George H. > I wrote about it and more here:http://webpages.charter.net/dawill/tmoranwms/Elec_Magnetics.html > Should be useful to lots of people who, like you, never got instruction in > what the hell a real transformer or inductor is, or how to design one. > > > Say it seems like toriods are the perfect topology for inductors, do > > they make toriods with a built in air gaps? (It doesn't have to be > > air.) > > Well, mix 61 and 67 ferrites have low permeability. I'm not sure if that's > due to fillers or magnetic properties. The B-H curve shows a rather wide > hysteresis loop (about 7 Oe across), suggesting disturbingly high losses. I > don't think powdered irons are even that high, though they lose energy > through eddy current as much as hysteresis. > > Powdered irons could be said to have built in air gaps, since they're > usually made from a fine powder (like carbonyl iron, which is spheroidial), > compacted and bonded with a resin. The metal density might be 70-90%, I > suppose, which is a lot of airgap. Actually, I suppose density would have > to be at least 97% for most types, as there are powdered irons with mu_r >= > 75 (and I think I saw MPPs as high as 750, but those might be sintered, I'm > not sure). > > Tim > > -- > Deep Friar: a very philosophical monk. > Website:http://webpages.charter.net/dawill/tmoranwms
From: Jim Thompson on 14 Jun 2010 14:15 On Mon, 14 Jun 2010 10:50:58 -0700 (PDT), dagmargoodboat(a)yahoo.com wrote: >On Jun 14, 12:08�pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On- >My-Web-Site.com> wrote: >> On Mon, 14 Jun 2010 09:49:09 -0700 (PDT), dagmargoodb...(a)yahoo.com >> wrote: [snip] >> >> > � � � � Vcc = +5v >> > � �--+--------------+------+-- >> > � � �| � � � � � � �| � � �| >> > � � �| � � � � � � �| � � .-. >> > � � �| � � � � � � �| � � | | e.s.r. = 1 ohm >> > � � �| � � � � � � �| � � | | >> > � � �| � � � � � � �| � � '-' >> > � � �| � � � � � � �| � � �| >> > � � �| � � � � � � �| � � �|_ || >> > � � �| � � � � � � �| � � � _)|| >> > � � .-. � � � � � �--- �L1a _)|| >> > Rb �| | � � � � C1 --- �1mH _)|| >> > 47k | | � � � � 1uF | � � � _)|| >> > � � '-' � � � � � � | � � � _)|| >> > � � �| � � � � � � �| � � *| �|| >> > � � �| � � � � � � �'---+--' �|| >> > � � �| � �R1 � � D1 � � | � � || >> > � � �| � 220r �schottky | � � || >> > � � �+--/\/\/----|>]----+ � � || >> > � � �| � � � � � � � � �| � � || >> > � � �| � � .------------' � � || >> > � � �| � |/ � � � � � � � � � || >> > � � �+---| � �Q1 � � � � � � �|| >> > � � �| � |>. 2n3904 � � � � � || >> > � � �| � � | � � � � � � � * �|| >> > �C2 --- � �+----------------. || >> > 1uF --- � �| � � � � � L1b �_)|| >> > � � �| � � | � � � � 100nH �_)|| >> > � � �| � � | � � � � � � � | >> > � � === � �| � � � � � � �=== >> > � � � � � �| >> > � � � � � �'--------------------> 5KHz output >> >> >Cheers, >> >James Arthur >> >> [snip LTspice Schematic] >> >> James, �How can you call it "class-A" when the emitter current is >> _not_linear_, _not_linear_, _not_linear_, _not_linear_ !! > >True, the emitter current isn't linear, but it is continuous and non- >zero, so I call that "class-A." > > >> All you've done is use a Schottky bypassing the C-B junction... >> otherwise it's identical. > >That makes a big difference. It prevents Q1 saturating and from >conducting b-c. And, without it Q1 conducts in reverse mode during >negative peaks, making the i(c) not just discontinuous, but reversing >in direction. That loads the tank, obviously. "Obviously"? Q1 doesn't conduct in reverse with your values, but no Schottky... the current is always out of the emitter... though it does get awfully close to zero: -376uA and -12.5mA peak. > >> I liken such oscillators to how you push your kid on a swing set. >> Giving a "nudge" every cycle. > >That's exactly how I think of them too. A "nudge" each cycle (short >conduction cycle) is what I did first. I call that "class-C." > >> To be "class-A" you'd need to sit upon the top bars and _continuously_ >> push and pull the ropes. > >Or you can pull continuously, harder at some times, not as hard at >others. That gives the swing position a d.c. bias, but is otherwise >the same, yes? Class-A implies _linear_, does it not? Or do we have a Larkin definition for today ?:-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: Archimedes' Lever on 14 Jun 2010 14:41 On Mon, 14 Jun 2010 11:15:00 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: > >Class-A implies _linear_, does it not? Or do we have a Larkin >definition for today ?:-) > > ...Jim Thompson What a lark.
From: dagmargoodboat on 14 Jun 2010 15:27
On Jun 14, 1:15 pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My- Web-Site.com> wrote: > On Mon, 14 Jun 2010 10:50:58 -0700 (PDT), dagmargoodb...(a)yahoo.com > wrote: > > > > > > >On Jun 14, 12:08 pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On- > >My-Web-Site.com> wrote: > >> On Mon, 14 Jun 2010 09:49:09 -0700 (PDT), dagmargoodb...(a)yahoo.com > >> wrote: > [snip] > > >> > Vcc = +5v > >> > --+--------------+------+-- > >> > | | | > >> > | | .-. > >> > | | | | e.s.r. = 1 ohm > >> > | | | | > >> > | | '-' > >> > | | | > >> > | | |_ || > >> > | | _)|| > >> > .-. --- L1a _)|| > >> > Rb | | C1 --- 1mH _)|| > >> > 47k | | 1uF | _)|| > >> > '-' | _)|| > >> > | | *| || > >> > | '---+--' || > >> > | R1 D1 | || > >> > | 220r schottky | || > >> > +--/\/\/----|>]----+ || > >> > | | || > >> > | .------------' || > >> > | |/ || > >> > +---| Q1 || > >> > | |>. 2n3904 || > >> > | | * || > >> > C2 --- +----------------. || > >> > 1uF --- | L1b _)|| > >> > | | 100nH _)|| > >> > | | | > >> > === | === > >> > | > >> > '--------------------> 5KHz output > > >> >Cheers, > >> >James Arthur > > >> [snip LTspice Schematic] > > >> James, How can you call it "class-A" when the emitter current is > >> _not_linear_, _not_linear_, _not_linear_, _not_linear_ !! > > >True, the emitter current isn't linear, but it is continuous and non- > >zero, so I call that "class-A." > > >> All you've done is use a Schottky bypassing the C-B junction... > >> otherwise it's identical. > > >That makes a big difference. It prevents Q1 saturating and from > >conducting b-c. And, without it Q1 conducts in reverse mode during > >negative peaks, making the i(c) not just discontinuous, but reversing > >in direction. That loads the tank, obviously. > > "Obviously"? Yeah, if Q1 sucks energy out of the tank, that loads the tank. > Q1 doesn't conduct in reverse with your values, but no > Schottky... the current is always out of the emitter... though it does > get awfully close to zero: -376uA and -12.5mA peak. Huh. LTSpice says Q1 does conduct in reverse, a nasty little 5mA spike's worth. The schottky feedback prevents that by cutting the base bias enough to make sure the collector never gets that low. > >> I liken such oscillators to how you push your kid on a swing set. > >> Giving a "nudge" every cycle. > > >That's exactly how I think of them too. A "nudge" each cycle (short > >conduction cycle) is what I did first. I call that "class-C." > > >> To be "class-A" you'd need to sit upon the top bars and _continuously_ > >> push and pull the ropes. > > >Or you can pull continuously, harder at some times, not as hard at > >others. That gives the swing position a d.c. bias, but is otherwise > >the same, yes? > > Class-A implies _linear_, does it not? Or do we have a Larkin > definition for today ?:-) I've always used "class-A" to mean the transistor conduction angle = 360º. Class-B means mostly conducting but sometimes 'off', and Class- C means 'mostly off.' -- Cheers, James Arthur |