Inductance or Inductance Factor (Al) value of ferrite core transformer? - Page 1
Forum section: electronics / beginners

author: ambi
author_rank: Newbie
timestamp: May 13, 2015, 05:01:36 am
content: Could any one pl tell me that what can be the inductance or Al value of ferrite core transformer of the below attached circuit?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 13, 2015, 05:54:58 am
content: Dat cropping...It's not obvious what maximum frequency it's supposed to run at (this is a blocking oscillator type flyback... with no active current limit, yeech -- don't be surprised if it catches fire on a hot summer's day some time), but I would guess around 100kHz, so the on-time has to be 5us or so, max. 25W capacity suggests a peak current of 1A, so at 120V minimum DC supply, 600uH primary. 100 turns then has A_L = 60nH/t^2.An EE28 core seems awfully large for the power level, so it should be easy to do this with a smaller core, or have plenty of extra space for insulating tape and whatnot.Tim

author: ambi
author_rank: Newbie
timestamp: May 13, 2015, 06:35:44 am
content: hiii @T3sl4co1l ... i am bit confused..check the image which attached below ... according to you it shows 1.4mH @100kHz .. pl rectify me if am wrong at any part of understanding the concept...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 13, 2015, 07:48:48 am
content: Dat cropping, again, tho...The original said 100-240V *AC*, which is 140-320VDC.If you only want operation at 240VAC, you can go with an inductance around there. You will probably get less output current if operated at a lower voltage.If you turn down the "Vin for calc" to the lower end, you will find it will run in CCM, which the circuit will not do. It needs to be DCM over the entire range.Tim

author: Richard Head
author_rank: Frequent Contributor
timestamp: May 13, 2015, 09:47:43 am
content: I'm not so sure the bipolar can do 100kHz. Probably more likely to be in the 30Khz region. I pressume the device is an MJE13005 equivalent. Terrible storage time with these devices.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 13, 2015, 12:52:32 pm
content: I ran a circuit like this at 200kHz before (using something like MJE18008, or something... see below). That was with nice and crisp base drive from the feedback winding. That might not be available here (the resistors in the feedback circuit seem to suggest so!), and a much lower frequency would seem to pair with the unusually large transformer.So hey, maybe A_L is even more than that!Another way to approach it: find A_e for the core in question, and find out what the lowest frequency is before saturation (or some modest value of Bmax like 0.2T). Then solve for air gap, and therefore A_L.Probably, somewhere between these two constraints will be the actual intended value.(Ref:http://seventransistorlabs.com/tmoranwms/Circuits_2010/RegBO.pngTransformer was some oddball EE core pulled from, I think, an ATX PSU's 5V standby circuit. I didn't have to gap it, and it didn't seem to have any gap at all, but the A_L was just right for this purpose -- not sure if it's a low-mu ferrite, or a powdered iron EE shape, or what!Also, no active current limit. Living dangerously! ...As it happens, I built a PCB for this thing, back in the day; but I never really got it to work, and didn't try to fix it.)Tim