Author Topic: SMPS based on TOP232 (Read 3833 times)

wraper · « **Reply #25 on:** March 19, 2020, 07:17:31 pm »

Quote from: masterx81 on March 19, 2020, 07:15:20 pm

But why on the top232 datasheet the secondaries are polarized inverted from the primary?

Because it's how flyback converter works. If it's opposite, you get forward converter.

masterx81 · « **Reply #26 on:** March 19, 2020, 08:03:18 pm »

So, that's why you was suggesting to simply invert the primary winding. Maybe the controller increase the dc a lot for try to have enough "negative part" of the flyback to reach the 5v.
Buh how recognize on the fly a flyback converter from a forward converter? Looks so similar.

wraper · « **Reply #27 on:** March 19, 2020, 08:09:31 pm »

The simplest would be according by PWM controller model.

masterx81 · « **Reply #28 on:** March 19, 2020, 08:18:27 pm »

Perfect, was hard, but (maybe?

) i've learned something

If it's a flyback, i'm sure that the the windings are wrong as i've wound them all on the same direction.
Try to invert the primary tomorrow.
Really thanks!!

wraper · « **Reply #29 on:** March 19, 2020, 08:20:28 pm »

TOP232 is flyback controller. It's not supposed to work as forward converter.

Circlotron · « **Reply #30 on:** March 20, 2020, 03:11:27 am »

Quote from: masterx81 on March 19, 2020, 08:03:18 pm

Buh how recognize on the fly a flyback converter from a forward converter? Looks so similar.

A flyback converter has no filter inductor. The rectifier diode on the output side feeds straight into a big capacitor. This is because the transformer secondary winding of a flyback converter is a current source, with a forward converter it is a voltage source.

wraper · « **Reply #31 on:** March 20, 2020, 03:21:04 am »

Quote from: Circlotron on March 20, 2020, 03:11:27 am

A flyback converter has no filter inductor. The rectifier diode on the output side feeds straight into a big capacitor.

You need to be aware that flyback often has inductor as well. Just a bit later in the circuit for noise filtering purposes. So simply presence of inductor does not mean anything unless you checked how it's actually connected. Though inductor in forward converter most likely will be larger in size.

masterx81 · « **Reply #32 on:** March 22, 2020, 08:41:48 pm »

Inverted the primary and now i have 15v on control line and 5v on the output. Perfect!
Thanks for the help and for the expalaination on how works smps transformers!
EDIT
Still something wrong... it start, i have clean 5v and 15v on the outputs, then after 10/15 seconds the output goes down. If i power off, it start working ok during the main filter capacitor discharge like before... it start working when voltage goes down at near 200v. Seem temperature dependant, if i do it when cold seem work longer than doing several tries. I not see nothing overheating

masterx81 · « **Reply #33 on:** March 23, 2020, 10:59:30 am »

Leaving it connected it works for 10/15 sec, then turn off, after few seconds start working back for 5 sec, and so on. Seem a protection triggering. It's not an overtemperature.
I attach the waveform of the primary side. The waveform seem good (no strange duty cycle, in the 29% region with 220vac input). I not see any appreciable variation in the waveform before shutting down.
With 180vac i have a duty of near 34% and it does the same thing (on-off-on-off etc).
I attach also the waveform when it's not working...
What sort of protection can be?
Thanks!

PKTKS · « **Reply #34 on:** March 23, 2020, 11:17:46 am »

Quote from: masterx81 on March 23, 2020, 10:59:30 am

I attach the waveform of the primary side. The waveform seem good (no strange duty cycle, in the 29% region with 220vac input). I not see any appreciable variation in the waveform before shutting down.
(..)

**IF** this was your first post on the subject...
with just the waveform ...
asking for guesses...

I would just say:
- by the waveform - THIS IS AN RCC (not a forward converter)
- and pretty much RCCs gone haywire with bad parts...
- a minor aged component or with different/changed values for RCC steady state....

if I was just looking that waveform and ignoring the rest...

go figure why this chip behaves like RCC...

Paul

masterx81 · « **Reply #35 on:** March 23, 2020, 11:33:06 am »

Seem a flyback converter (for sure as the primary of the transformer is out of phase from the secondaries, also in the pdf).
The smps ic have really few components around it. I attach a photo of the d**n thing.

masterx81 · « **Reply #36 on:** March 23, 2020, 11:39:24 am »

D18 is the rectifier of the 5v output, c39 is the 5v smoothing cap, u2 optocoupler, d17/c36 rectifier of 15v control voltage, c41 and r56 seem an rc filter (not tuned, same values of the pdf), d19/d20 as per pdf. C35 seem a 300v smoothing cap placed near the smps. C42 smooth the input voltage of the smps ic.

masterx81 · « **Reply #37 on:** March 23, 2020, 02:51:26 pm »

I've checked the pdf and i've not seen any requirement about needed inductance, and neither nothing about capacitors to "tune". But from pdf the switching frequency must be typ 124-140khz, while i've measured around 107khz.

PKTKS · « **Reply #38 on:** March 23, 2020, 03:27:09 pm »

Quote from: masterx81 on March 23, 2020, 02:51:26 pm

I've checked the pdf and i've not seen any requirement about needed inductance, and neither nothing about capacitors to "tune". But from pdf the switching frequency must be typ 124-140khz, while i've measured around 107khz.

They all do. Implied on design of flybacks.

But we have today a off-the-shelf ready numerated coils to choose.

Another shot:
- using that TL431 transconductance error amplifier...
- Try to play the feedback loop current to voltage ratios...

Eventually you may have luck tuning the FB loop itself
for steady state operation at some load ranges.

Paul

masterx81 · « **Reply #39 on:** March 23, 2020, 07:17:22 pm »

Quote

Oscillator and Switching Frequency
The internal oscillator linearly charges and discharges an
internal capacitance between two voltage levels to create a
sawtooth waveform for the pulse width modulator. The
oscillator sets the pulse width modulator/current limit latch at
the beginning of each cycle.
The nominal switching frequency of 132 kHz was chosen to
minimize transformer size while keeping the fundamental EMI
frequency below 150 kHz.

The internal oscillator is not tied to the inductance. Is linearly charged and discharged, i think by an internal resistor.

The feedback loop has nothing strange or that can be tuned. Filters and resistors, and the optocoupler. And in any case the voltages of the feedback are good (5v and 15v).

Really, i think to remove that damn thing and put an external trasformer!

shakalnokturn · « **Reply #40 on:** March 23, 2020, 07:39:59 pm »

Have you checked transformer's temperature itself?
Primary winding too thin?

masterx81 · « **Reply #41 on:** March 23, 2020, 08:28:06 pm »

The original winding was measured with a precision micrometer... i've checked by hand and with an infrared gun and nothing more than 35*c.

shakalnokturn · « **Reply #42 on:** March 23, 2020, 08:58:54 pm »

New TOP232 came from a reliable source?

masterx81 · « **Reply #43 on:** March 24, 2020, 12:10:39 am »

Ehm, not. Ebay or aliexpress... i try to find a different smps ic...

masterx81 · « **Reply #44 on:** April 01, 2020, 03:42:33 pm »

Replaced the smps ic with one new of the same batch, ad it works. The temperatures are low. All seem ok.
Thanks to all for the help!
I've lost some time but i've learned a lot of things


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Author Topic: SMPS based on TOP232 (Read 3833 times)

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