SYMSI70 gas heater, TOP247Y exploded, power supply, snubber network

[hikomalek]

Hello, I have a SYMSI70 gas heater board, which has issues with its primary side power supply, controlled by TOP247Y chip.
When I replace a TOP247Y it explode in 1 second. I have desoldered transformer and measured a winding ratio, so transformer looks like OK.

Transformer:

|Info| Primary | Aux | AB | CD|
|-|----------|----------|-|-|
|Ratio|1|25|40|12|
|Voltage AC|230V|9.2V|5.8V|19V|
|Voltage DC (*1.41)|230V|13V|8.1V|27V|

I have disabled a undervoltage protection of TOP247Y, disconnected secondaries and tried to power it up with voltage from 50 to 150V DC (I have connected in series multiple 32V DC printer power supplies).
When I connected all secondaries, all voltages were correct, display was showing an error "F10" as nothing was connected and "some relays" on board were switching. So board works correctly on 150V DC.
A Drain-Source current(on primary side) was about 50mA, power consumption about 8W. On the board, nothing is hot, so there are no hot components.
But when I connected it to 230V AC, which is about 325V DC, TOP247Y exploaded. This happen everytime. I have another older board which has some "logic issues" and chip TOP247Y works correctly in this old board, so the chip TOP247Y is not broken.
I have transformer out of the board on about 30cm wires.

It means that error must be in a snubber network, there are two, one around a transformer and the second around a Drain-Source of TOP247Y chip. I do not have ESR meter or oscilloscope, I have only simple "Non-True RMS multimeter".

I have even tried to put a P6KE300A tvs diode to primary snubber network,
Diode BA159 was OK, but I have replaced that with UF4007.
Snubber capacitor C803 (10n) I have replaced with two 6.3nF 400v capacitors
Second snubber capacitor C1, about 70pF was "white SMD ceramic MLCC" I have replaced with "simple ceramic" which is probably for low voltage only.

When I'm measuring voltages even with 50V DC power supply, snubber voltages are high, about 200-500 V on multiple places.

I have some P6KE130A (tvs diode), should I use it?

How can I check it safety? I wanted to use a tyristor dimmer to slowly rise a voltage (I do not have a variac), but it is just cutting some pieces of waves and does not limit max voltage, so TOP247Y exploded too. So I'm thinking of using some "capacitive divider" to make a lower voltage.

So there is no overcurrent, just an overvoltage caused by a snubber network malfunction. Please what can I do with that? Everything looks like correct

[CapLeaker]

Means Jack sh*t to me. These TOP, LNK, TNY etc switchers are quite delicate. If the board isn’t hospital grade clean in between the pins, the switcher will also just fail. I fixed a device where someone else didn’t properly clean around the pins. device ran for a few hours and bang, the switcher went. I did the second repair and it is still running today 24/7/365.
make sure everything is absolutely clean. The problem with these TO220-6 is that the pins are too close together, HV doesn’t have to work hard in order to get into a different pin. To me these TO220-6 is the worst design ever.
I wouldn’t disable UVLO etc. Snubber caps I always replace them with the same value, but 2KV rated. Symptoms of TOP etc, lid blown off to looking brand new but still dead. Had found them do all that on various devices. Good luck!

[stj]

topswitches have a long history of exploding in 2 situations.
1: poor startup capacitor causing it to hickup till the boom.
2: low supply voltage causing it to not start oscillating properly.

[stj]

just a thought,
make sure it's getting smooth 340v-ish dc,
a bad rectifier or input cap could blow one.

[hikomalek]

Thank you all for your responses.
Regarding disabling under voltage protection (UVLO), I had to do that, because I was testing that on "low voltage", to prevent explosion. At 50V Drain-Source current was 200mA, at 150V just about 50mA. TOP247YN was not hot (it has even nice heatsink).

About clean board and between pins/board track interaction. Is it real? Yes, when measuring by multimeter, Drain-Source voltage is over 1000V (so my multimeter, cannot measure it), at least multimeter didn't break yet. My board looks like very bad, as I broke a board tracks, so I had to "replace them" by thick wires. But I consider, the distance between them is "large" and nothing bad can happen.

About smooth 340V DC at the input. Last time I wanted to test it on higher voltage (more than 150V, as I do not have more printer power supplies). So I had an idea to use a diac-thyristor dimmer, to regulate an input voltage. I was aware that it is just cutting the output, but not limiting an amplitude (which is still 325V). But I set it to minimum, which can be about 40V (diac threshold). And at this configuration TOP247YN exploded in a second. So when I was powering it by 150V DC it was working correctly, but about 40V AC (with 325V peaks) broke that.

But what about snubber network and TVS diode? I would expect that as I have a tvs diode P6KE300A around a primary winding, voltage should not be so high. I have a P6KE130A, should I use it? Then I guess, max primary winding voltage will be 130V + 325V from "mains" so about 450V.

Is it possible to use an external MOSFET and drive it using a TOP247YN (maybe drain)?

This power source has output voltage of 8V (for a logic) and 27V (for relays), then, it is driving a fan which blowing an air, I guess this can be PWM controlled. So maybe TOP247YN is powering this fan too.
A have tried connect 8V and 24V external power supplies to transformer output and it was working (but of course without connecting a board to gas heater).


Is there any way how to test it and do not break it again?
How to get a DC voltage of 200V or 300V? I do not have a variac.

I will try to put insulated tube to each TOP247YN pin and clean a board. And I replace an input smooting capacitor (after a rectifier).


Thank you :-)

[CapLeaker]

First: no… you can’t replace a 300V transient diode with a 130V one.
Second: while I do have a variac, I hardly ever use it. Mostly we are using the incandescent dim bulb current limiter in series trick. If there is a lot of current drawn, the incandescent bulb will limit the current to the PSU and light bright. Since this is a small power supply you need a low wattage incandescent bulb.

[stj]

a variac can kill a topswitch, keep it for valve based stuff..

[Agent24]

About clean board and between pins/board track interaction. Is it real? Yes, when measuring by multimeter, Drain-Source voltage is over 1000V (so my multimeter, cannot measure it), at least multimeter didn't break yet. My board looks like very bad, as I broke a board tracks, so I had to "replace them" by thick wires. But I consider, the distance between them is "large" and nothing bad can happen.

Show us a photo of this area... It doesn't matter if the distance is large, the pins are still close together in the end, and if they are not clean (flux residue etc) there can be leakage current that turns into electrical breakdown and failure.

[hikomalek]

Hello, so update.
As you have mentioned, it likes smooth input DC voltage.
- Input smoothing capacitor (after a rectifier) was wrong, it has about 50nF capacitance and it should be 47uF. I have replaced it with some other.
- removed a TVS diode (there was not any TVS diode before)
- replaced faster diode UF4007 by a slower BA159 (original), maybe too fast is not good, even somewhere there are using just a 1N4047
- enabled UVLO protection

And it didn't exploded immediately! But later I was disconnected and connected Drain, to "Primary of transformer" when it was turned on and now TOP247Y is shorted... Probably, I have connected that at the time when it was switching with high duty after a restart, so there was a high current suddenly.


But I have another board (older), that one have working TOP247Y chip (last one). I thought that board has some logic error, but it looks like that secondary smoothing capacitor was bad, so I have replaced capacitors and relays are not switching as crazy as before (maybe relays didn't have enough power).

Now on secondaryB there is a voltage on smoothing capacitor about 42V, which is I guess too high. Capacitors are rated to 35V, there is LM317, which is only to 40V.
I have a feeling, that when i was powering that with a lower DC voltage on this secondaryB was about 28V.

There is no feedback from secondaryA and secondaryB to TOP247Y. Only AUX has a feedback, by about 6V zener diode, so after AUX rectifier diode there is 12V.
So voltage on secondaryA and secondaryB is only based on transformer winding ratio and "power transfer" among AUX and secondaryA and secondaryB.

What can cause a higher voltage on secondary? Can it be a higher current on AUX, so more "power" is transferring to both secondaries?

I think the issue is again in capacitors. I do not have an ESR meter (I have a plan to make it soon). My components come from a scrap from electric trash.
I'm expecting new TOP247YN from China next week (10 pieces by 0.86 EUR). In our local shop one TOP247YN is for about 5 EUR and 8 EUR postal fee.

Thank you for your valuable info, it was useful...

Good document about power supply:
https://www.onsemi.com/pub/collateral/and8461-d.pdf

[CapLeaker]

Switching out UF4007 to a BA159 isn’t a good idea as the recovery time is much higher on the BA159. If there was a slower diode in there, you can certainly switch it out for a faster one.