Flyback IC not oscillating transformer primary coil so no voltage on secondary

Thread Starter

jlawley1969

Joined Feb 22, 2021
78
Hi, I am using TOP257YN to prototype a flyback transformer circuit. I am ultimately going to be using the surface mount version but right now I just want to a proof of concept point. So my diagram is a little different from my actual circuit I am testing. The main difference being X and F pins are being jumped to the source pin which is grounded.

That just to get that all out of the way. My issue is that the TOP IC is not "firing" as in the signal I am measuring with the primary referenced to ground is not oscillating at 132kHz like it is supposed to(or oscillating whatsoever) so I am not seeing any voltage on my secondary. I am however seeing voltage on my bias winding(using a 750871110 transformer) but at about 5V instead of the 10V it is rated for. Nothing is obviously wrong with my breadboard wiring but I am continuing to comb it. One weird thing is that the breadboard RAIL that the D pin is on is getting 160Vdc and other components on that rail are getting 160V except the D pin itself is only reading like 28V. I measured resistance between the pin and the rail and it is 0Ohms according to my multimeter.

Im just looking for a point in the right direction for this one because I believe it should work.
 

Attachments

AlbertHall

Joined Jun 4, 2014
11,538
If there were different voltages on the pin and the rail then they are not connected. I suspect a dodgy connection on the breadboard to the D pin and whne you probed for ohms the pressure of the probe caused them to connect properly.
 

Thread Starter

jlawley1969

Joined Feb 22, 2021
78
If there were different voltages on the pin and the rail then they are not connected. I suspect a dodgy connection on the breadboard to the D pin and whne you probed for ohms the pressure of the probe caused them to connect properly.
thank you Ill switch to a different board
 

Thread Starter

jlawley1969

Joined Feb 22, 2021
78
changed to a new board
the D pin is now getting the voltage but still has a similar issue of nothing on the secondary or bias winding :(
 

dcbingaman

Joined Jun 30, 2021
475
When breadboarding a simple circuit using a solderless breadboard that contained multiple LDO's, I was getting strange behavior. (LDO not working correctly). It turned out the problem was multiple 'ground paths'. When I had removed the multiple ground paths the problem was corrected. Being that your circuit is considerably more complex you might be running into a similar issue. Recheck your wiring and also try to eliminate any multiple ground paths from the breadboard. Keep your wiring as short as reasonably possible may help also.
 

Thread Starter

jlawley1969

Joined Feb 22, 2021
78
When breadboarding a simple circuit using a solderless breadboard that contained multiple LDO's, I was getting strange behavior. (LDO not working correctly). It turned out the problem was multiple 'ground paths'. When I had removed the multiple ground paths the problem was corrected. Being that your circuit is considerably more complex you might be running into a similar issue. Recheck your wiring and also try to eliminate any multiple ground paths from the breadboard. Keep your wiring as short as reasonably possible may help also.
what do you mean by multiple ground paths?
 

dcbingaman

Joined Jun 30, 2021
475
what do you mean by multiple ground paths?
More than one connection across the wireless breadboard that end up forming loops. It simply means there is more than one electrical connection between a 'ground' pin say on a chip and the 'ground plane'. It usually is not a problem on solderless breadboards. But on large solderless breadboards that have feedback loops say for maintaining constant voltage or current outputs, any extra wires can cause inductance coupling noise that can mess up the circuit. For switching power supplies these are usually built on a PCB with a nice large ground plane so all of the impedances are well controlled. This is generally not the case on a solderless breadboard. Also really long ground wires on a critical circuit (such as a switching power supply) can lead to problems.
 

MisterBill2

Joined Jan 23, 2018
9,535
I am guessing that the 8 pin dip needs feedback to oscillate, and that the feedback is to pin 1. Any function labels are far to small to read in the schematic. The opto-isolator will be OFF until it gets some bias and there will be no bias until it is oscillating.
In addition, the feedback loop does not look right at all.
 

Thread Starter

jlawley1969

Joined Feb 22, 2021
78
I am guessing that the 8 pin dip needs feedback to oscillate, and that the feedback is to pin 1. Any function labels are far to small to read in the schematic. The opto-isolator will be OFF until it gets some bias and there will be no bias until it is oscillating.
In addition, the feedback loop does not look right at all.
did you look at the data sheet or are you just shooting? https://ac-dc.power.com/sites/default/files/product-docs/tophx_family_datasheet.pdf
 

MisterBill2

Joined Jan 23, 2018
9,535
No, I did not look at the data sheet. I looked at the circuit drawing and the only line that resembles a fewedback line is the one through the opto-coupler. The line to pin one will not have anything close to a feedback signal until the transformer flux is changing. The line to pin 2 will have no signal until the opto-isolator is biased, The line to pin 4 looks like it connects to the switch for the transformer current. If pin "D" (pin#4) only is getting 28 volts then there is a lack of continuity between the pins on the transformer at 160 volts and pin 4 on the IC.
 

Thread Starter

jlawley1969

Joined Feb 22, 2021
78
anyways for the people who read the rest of the thread
I tried the same circuit but with TOP224 (which is just a more baredbones version of the TOP257) and it would work for a few moments and then essentially go to fault mode.
I then switched the output diodes to fast recovery(600v1A) for the bias and schottky (30v5A)for the secondary aswellas swap the wires on the primary from one to the other
not sure which one did it but I am getting 5.5V on the secondary consistently.

the issue now is that the bias winding should be putting out 10v as per the data sheet but it is giving a very solid 6V on top of this the TOP224 was getting literally too hot to handle. I wouldnt say that hot but definately something is wrong.
but that is something I will look into on monday thank you everyone for your help thus far.
 

MisterBill2

Joined Jan 23, 2018
9,535
Ikr they couldnt even manage to read post #4
As a matter of fact, SB, I read through every one of them. And while others commented that there must be a failed connection some place, there were also circuit issues that would be a problem if all the connections were good.

And it seems that you still get off throwing stones.
 

shortbus

Joined Sep 30, 2009
8,886
As a matter of fact, SB, I read through every one of them. And while others commented that there must be a failed connection some place, there were also circuit issues that would be a problem if all the connections were good.

And it seems that you still get off throwing stones.
He gives a link to the Data sheet and you answer with some random thing, and I'm throwing stones? Maybe if you didn't post so many glass houses I wouldn't be like this.
 

jlawley97

Joined Oct 5, 2019
19
Is there a reason your not using the recommended transformer for that chip? The one you picked doesn't seem like it is even close to the recommended one - http://datasheet.datasheetarchive.com/originals/library/Datasheets-UD3/DSAUD0041905.pdf Information from here - http://13.124.15.139/?q=TOP224+Application+Note
mostly because of the sie, but also I do not understand transformers that much. Aswellas the fact that for the TOP257 only reccomends the bobbin and the application notes tell you how to design the transformer where as I want to use an off the shelf component. on TOP of that so many transformers are sold out.
Does the inductance matter more than the turns ratio in the transformer?
 
Top