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Needing to wind flyback transformer for scope clock project.

Thread starter #1
Hello, im in the process of ordering the parts for this "open source" scope clock.
it needs a custom wound flyback transformer, since im building this kit from scratch with the PCB's ive ordered from a manufacturer myself and ordering the components from Mouser.

I have no idea on the footprint of the type of transformer, the ferrite cores etc, all i know is its 8 pins and sits rather flat on the PCB, can probably work out the dimensions from the eagle files.
going by the schematic, its got a 12v primary and 150v secondary to give 300VDC through a voltage doubler and a second 70v secondary for the grid supply.

Anyway, im useless with transformer theory, but have all the wire in the world and just need to know the number of turns and the correct size core.
Any ideas?
See photos below
Link to project is here http://www.sgitheach.org.uk/scope3.html
They have a dropbox link to all the documentation, but dont see anything regards the transformer https://www.dropbox.com/sh/rldue6seyzty9ju/AACBYwL82EpUBx_-eqVYwkpCa?dl=0
schematic psu.jpg flyback.jpg
 

unclejed613

Well-Known Member
Most Helpful Member
#2
it's a simple matter of finding turns ratios. 150/12=12.5 so if your primary is 10 turns, your HV secondary will be 125 turns. for the grid supply 70/12=5.83, so the grid secondary will be 58 turns.
you should use 16 or 18 AWG for the primary, and 24 or 28 AWG for the secondaries. in the [data sheet] the value for the primary is shown as 22 to 85 microhenries, so if you can get a reasonably small number of turns (10 to 20) to equal a value in that range, it should work. all you would need to do is take the number of primary turns and multiply by 12.5 and by 5,8 for your secondary turns counts. the LM2588 operates between 100 and 400khz, so you will need very fast diodes.
 
Last edited:
Thread starter #3
it's a simple matter of finding turns ratios. 150/12=12.5 so if your primary is 10 turns, your HV secondary will be 125 turns. for the grid supply 70/12=5.83, so the grid secondary will be 58 turns.
you should use 16 or 18 AWG for the primary, and 24 or 28 AWG for the secondaries. in the [data sheet] the value for the primary is shown as 22 to 85 microhenries, so if you can get a reasonably small number of turns (10 to 20) to equal a value in that range, it should work. all you would need to do is take the number of primary turns and multiply by 12.5 and by 5,8 for your secondary turns counts. the LM2588 operates between 100 and 400khz, so you will need very fast diodes.
Thanks for that.
I had been doing some rough calculations and thats fairly close to what ive got. Just dont know where I can find the correct core and bobbin that will fit on the board.
I also believe you need the correct bobbin with a divider to seperate the two secondarys?
 

dr pepper

Well-Known Member
Most Helpful Member
#4
If you can find the type of transformer then I might be able to run it through my smps transformer calc software for you, I also need the switching frequency I seem to recall that chip can go up to 200kc.
The only imprtant bit is to get the primary turns right, so you make use of the transformers core (coupled inductor for purists) but do not saturate it.
Check out datasheets for EFD series ferrite transformers, I think either philips or ferroxcube sell them.
 
Thread starter #5
If you can find the type of transformer then I might be able to run it through my smps transformer calc software for you, I also need the switching frequency I seem to recall that chip can go up to 200kc.
The only imprtant bit is to get the primary turns right, so you make use of the transformers core (coupled inductor for purists) but do not saturate it.
Check out datasheets for EFD series ferrite transformers, I think either philips or ferroxcube sell them.
OK sounds good, ive ordered their transformer for what its worth, but at least i will have a better idea if i ever build another one.
 

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