# Transformer construction diagram

Can anyone explain how the actual winding happens? The transformer is a shell type transformer used in a flyback circuit. The circuit is not working, and I'm suspecting the transformer, but I don't have a method to test the transformer. If anyone could help, that would be awesome.

From my preliminary examination, I found that the VDD is fluctuating from 12 to 5v, My inference from the datasheet is that the High voltage current source is helping till it reaches VDD(start) and turns off to let the bias voltage take over, but that's not happening, so it resets, and reinitiates the startup sequence and is in a loop. I'm getting roughly around 300V at the bulk caps after Full bridge rectifier and zero volts at the secondary. Kindly note this is a TI generated schematic. The PWM signals will drive the power Mosfet only when VDD Is at 14.7v. The dot convention shown in the schematic is wrong. The transformer was done according to the report which I have attached.

• Although I know what a transformer works and what it looks like, this drawing doesn't tell me much, it is that it says it concerns a transformer, I would never have guessed that. You suspect the transformer, WHY? Without you even showing your circuit (you should add it) I can name more than 10 things which could be wrong as well which are not the transformer. Sep 13, 2019 at 6:23
• @Bimpelrekkie let me know if you need anything else. Sep 13, 2019 at 6:32
• XY problem! Why why why would you come to the conclusion it’s the winding construction? Sep 13, 2019 at 6:38
• From my preliminary examination, I found that the VDD is fluctuating from 12 to 5v, My inference from the datasheet is that the High voltage current source is helping till it reaches VDD(start) and turns off to let the bias voltage take over, but that's not happening, so it resets, and reintiates the startup sequence and is in a loop. I'm getting roughly around 300V at the bulk caps after Full bridge rectifier and zero volts at the secondary. Kindly note this is a TI generated schematic. Sep 13, 2019 at 6:43
• The diagram of the transformer doesn't indicate whether the windings go clockwise or anticlockwise from 'start'. If you think the dots are in the wrong place, try reversing some of the windngs. This is your 'method to test the transformer'. The sketch of the transformer only helps if it is assured that all the windings go round the same way from 'start'. Sep 13, 2019 at 7:03

I have seen several diagrams like this but this one is confusing.

It doesn't tell you the size of wire, the start and finish do not match the circuit diagram and the number of turns is not explicitly given though you may be able to count them from the drawing. It also does not explicitly state the core and bobbin.

My best guess would be as follows all winding start and end on the right and side of the bobbin.

Half the primary is wound first start on pin 3 wind 8 turns across the full width of the bobbin secure with a single layer of tape now wind back another 8 turns (16 total) and finish on pin 4.

Next we need basic insulation which typically may be 3 layers of tape.

Next we have the secondary start on pin 12 wind 8 turns across the full width of the bobbin, secure with tape, lay the wire back over the winding and finish on 9.

Next we need basic insulation which typically may be 3 layers of tape.

Next we have the auxilliary start on pin 6 wind 8 turns across the full width of the bobbin, secure with tape, lay the wire back over the winding and finish on 5.

Next we need basic insulation which typically may be 3 layers of tape.

The other Half the primary is wound first start on pin 4 wind 8 turns across the full width of the bobbin secure with a single layer of tape now wind back another 8 turns (16 total) and finish on pin 3.

Finakkt we need basic insulation which typically may be 3 layers of tape.

Fit the cores and you can test it. Typically flyback transformers are designed for a specific inductance which may require a controlled air gap depending on type of core.

To check inductance you need an inductance meter to check phasing and turns ratio you need a signal generator and scope or DVM. Using a DVM is more tricky as it won't show phase but by putting windings in series and swapping the phasing of one you will see that the output voltage is higher when both windings have the same phase.

Note: When this was originally written only the final construction drawing was in the question so this answer is based purely on that so the construction may have changed but this should illustrate the general approach.

I have answered your question about how wiring diagrams typically work and how to check a transformer but I am not convinced the transformer is necessarily the problem.

• the gauge of the wire is mentioned. Please check all the images and comments once again to get a better picture. Sep 13, 2019 at 7:47
• @JAGADISHK We shouldn't have to read through all the comments to get all of the information. You should edit your question and add all of the information there. Sep 13, 2019 at 13:07
• Thanks for pointing it out @Tyler, I have edited the question. Sep 16, 2019 at 5:56