# tutorial needed on how to wire a flyback transformer

#### hunterage2000

Joined May 2, 2010
487
I have been searching the net for a tutorial on how to wire a flyback transformer but can't find anything. I'm not sure on all the parts I need but the book I'm referencing from says use a PM #87 pot core with 1 primary side and 1 secondary. Can anyone point me to a good source?

#### hunterage2000

Joined May 2, 2010
487
Yeah I was going to make a variable flyback smps so I just need the one secondary. I have a few books on how to design them with examples but it doesn't actually go into how you make the transformer.

#### hunterage2000

Joined May 2, 2010
487
I'm following an example which gives specific spec values of:

Core size =PM 87
Center pole area Acp =700 mm2
Operating frequency =21 kHz
Total period =45µs
Maximum “on” period =33.3% (15 µs)
Minimum primary volts =280 V DC
Optimum flux density =0.15 T
Primary turns = 42
Secondary turns = 9

#### Alec_t

Joined Sep 17, 2013
14,010
If you have the PM87 core, then winding 42 turns and 9 turns, with insulation between the two windings, shouln't be too difficult?

#### hunterage2000

Joined May 2, 2010
487
Sorry actually what I have is a Pq core but I guess I can learn from this. I have attached the images of the core and a bobbin and the core fitted onto the bobbin. I think something is missing between the core and the bobbin but I don't know what.

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#### bertus

Joined Apr 5, 2008
22,233
Hello,

There should be two ferrite pieces.
They should have likey the same shape.
One on top and one from the bottom in the bobbin core.

Bertus

#### hunterage2000

Joined May 2, 2010
487
Yeah ok, I have the 2 parts now and the bobbin. What is the next step? I'm not sure if I'm asking the right questions but

1). how is the 2 parts held together?
2). I'm guessing that the copper wire is wrapped around each vertical section of the cores and around 2 pins on each side?
3). Is there insulation between the copper wire and the core?

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#### Jony130

Joined Feb 17, 2009
5,475
Ad2 - No, you winding the wire around this plastic bobbin.
Ad3 - We use isolation tape to separate the windings

#### hunterage2000

Joined May 2, 2010
487
I tried goggling transformer mounting clips/clamps and isolation tape but found nothing. Is there any guides on what I need to do? Not sure what you meant by wind around the plastic bobbin. I thought it would look like the attached image.

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#### Alec_t

Joined Sep 17, 2013
14,010

#### hunterage2000

Joined May 2, 2010
487
I can't figure out the steps it took to get to the finished product. I would of thought there would be some sort of step by step guide.

#### ian field

Joined Oct 27, 2012
6,536
I have been searching the net for a tutorial on how to wire a flyback transformer but can't find anything. I'm not sure on all the parts I need but the book I'm referencing from says use a PM #87 pot core with 1 primary side and 1 secondary. Can anyone point me to a good source?
There are various chips for flyback supplies, and most have published appnotes with a wealth of information.

Find the names of a few chip manufacturers and search their sites for flyback chips - the numbers you find are the basis for the next stage of searches.

#### Dodgydave

Joined Jun 22, 2012
11,151
There are various chips for flyback supplies, and most have published appnotes with a wealth of information.

Find the names of a few chip manufacturers and search their sites for flyback chips - the numbers you find are the basis for the next stage of searches.
Uc3842/43/44/45 series,are used in most laptop and mobile phone chargers, these use flyback smps, salvage one from these to get you started, or an old atx psu.

Application note AN1024 from international rectifier has information on transformers

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#### Colin55

Joined Aug 27, 2015
519
Designing and building a fly-back circuit is much more complex than you think. The output voltage is nothing to do with turns-ratio and you have to know what you are doing.
It's not for a beginner.

#### ian field

Joined Oct 27, 2012
6,536
Uc3842/43/44/45 series,are used in most laptop and mobile phone chargers, these use flyback smps, salvage one from these to get you started, or an old atx psu.

Application note AN1024 from international rectifier has information on transformers
When I repaired monitors, the 384x family were more common than all the others put together.

You have to watch the last digit - they all have UVLO, 1 of each series are for direct off mains - I think the UVLO is around 16V, the other 2 are for automotive - for that I think the UVLO is about 9.5V. One of each series does up to 100% M/S ratio - the other 2 only do 50%.

The MC34063 is a popular entry level control chip, it has an uncommitted output transistor so it can be a buck, a boost or an inverter.

#### szhighstar

Joined Jun 26, 2012
27
Sorry actually what I have is a Pq core but I guess I can learn from this. I have attached the images of the core and a bobbin and the core fitted onto the bobbin. I think something is missing between the core and the bobbin but I don't know what.
the core and bobbin are PQ type, these are common materials,do you have auxiliay winding? you cut off air gap on center leg of core.