LM2596 gets extremely hot

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3 months 1 week ago #11409 by Joker
I have now built the ClassicNixieClock Rev6
Unfortunately, after a short time something starts to oscillate.
The board starts to make a noise, the current consumption increases exponentially and IC1 (LM2596T) gets extremely hot.

What is the best way to limit the problem? Maybe the seller sent a wrong coil.
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3 months 1 week ago #11411 by Ian
Replied by Ian on topic LM2596 gets extremely hot
Those aren't the components that come with the kit, so I guess you have bought them to go with the PCB, which is mine. We need to go step by step.

First step, take all the socketed components off the board and check that if it still gets hot. Measure the voltage out of the 5V test point.

Here are some things to check:

The 2596 must be a 5.0V version - more common are the adjustable ones - please make sure that you have the 5.0V one.

Did you check the 5V line before populating the other components? Did it work before?

If nothing gets hot with the controller, optos and K155 out of the sockets, and if you see 5V on the test point, go to the next step:

Next put in the controller only. Again check 5V and that nothing gets hot. Check the HV voltage.

After that you can put in the optos and the K155, again check the 5V. Does anything get hot?

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3 months 1 week ago #11412 by Ian
Replied by Ian on topic LM2596 gets extremely hot
OK, when I enlarge the picture I can see that the 2596 is a 5V one. Good.

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3 months 1 week ago - 3 months 1 week ago #11413 by Joker
Replied by Joker on topic LM2596 gets extremely hot
Okay, you are right - back to the beginning.

1. Without:
- Wlan Modul
- Atmel
- Optocoupler
- Nixiedriver

the LED lights up.
5V on VCC
the currentconsumption is constant at about 0,01A
No Sound

2. additional nixiedriver plugged in
the currentconsumption is constant at about 0,025A

3. additional wlan-modul plugged in
the currentconsumption is constant at about 0,083A

4.additional Atmel plugged in
the currentconsumption starts at about 0,095A and increases slowly also the sound.

The Highvoltage starts at 48V and increases. At a consuption of 1A the Highvoltage is at about 170V und the board starts with the angry sounding


there are no tubes connected - can this be the reason that the high-voltage rail gets crazy due to a missing load?
Last edit: 3 months 1 week ago by Joker.

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3 months 1 week ago #11414 by Ian
Replied by Ian on topic LM2596 gets extremely hot
With no load applied it should work fine.

At what step does the 2596 get hot?

Leave the WLan module out of the story at the moment - everything should work just fine without it. When everything is solved we add that at the end.

So now we know that the 5V circuit is stable without the controller.

Please check the voltage rating of the capacitors. Especially the brown one.

My suspicion is that the HV capacitor has a voltage rating that is too low, or perhaps it is faulty.

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3 months 1 week ago - 3 months 1 week ago #11415 by Joker
Replied by Joker on topic LM2596 gets extremely hot
Hello, Ian,
thanks for your answer.

The wlan module was more nice to know - the 3.3V rail is working and the module is working too.

I have now removed the K155ID1 and noticed that the board goes crazy when i insert the Atmel.The 5V voltage remains constant until my power supply goes into the current limit at 1A. Apparently the Atmel is defective. Over Pin 7 and 8 5V are present. I still have a STK500 board - I will try to reach the Atmel tonight. Edit: I Powered the Atmel with 5V and the consumption was 0,03A - I think there is another problem.

The brown capacitor (C1) has 2.2µF 400V - this should be enough
Last edit: 3 months 1 week ago by Joker.

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