Hello, I created a trailing edge dimmer and after a few hours of lighting on the full brightness (MOSFETs fully on) the fuse blew up. After I measured the electrical components on the board I found also a blown resistor R5 and a short circuit in D1. What could go wrong with the circuit? Thank you.

 

What could go wrong with the circuit?

Is D2 also shorted or open? What about the mosfets?
Replace D1 with a 1N4001.

 

Exactly! The 1N4148 is a small signal diode, cannot handle the inrush currents during the power up.
As mentioned earlier use a 1N400x diode.

 

Is D2 also shorted or open? What about the mosfets?

D2 and mosfets seem ok.

Replace D1 with a 1N4001.

I can try to replace it but how would you explain the blown R5?

The 1N4148 is a small signal diode, cannot handle the inrush currents during the power up.

It handled the power up since it stopped working after a few hours.

 

I can try to replace it but how would you explain the blown R5?

It doesn't unless C6 is shorted then that would also blow out C2 through C5 and D2.

 

It doesn't unless C6 is shorted then that would also blow out C2 through C5 and D2.

You're right, I've just measured few hundreds ohms across C6 so I guess it is dead. Any idea why C6 is blown?

 

Any idea why C6 is blown?

Are any of the caps C2-C5 shorted?

 

Are any of the caps C2-C5 shorted?

No, they are fine

 

You said D2 seems OK, did you actually check to see if it's good? Any measurements?
Can you post the schematic in a jpeg or png format?

 

You said D2 seems OK, did you actually check to see if it's good? Any measurements?

Forward voltage 595 mV. In the opposite orientation, I measured nothing - open circuit (the multimeter probably can measure just a voltage on a normal diode).

 

What did it read using the ohmmeter?

 

What did it read using the ohmmeter?

Open circuit in both directions.

 

Open circuit in both directions.

Sounds like it's open Did you use the diode check input on the meter?
Also repost the schematic in a png or jpeg format please.

 

Sounds like it's open Did you use the diode check input on the meter?
Also repost the schematic in a png or jpeg format please.

Forward voltage 595 mV. In the opposite orientation, I measured nothing - open circuit (the multimeter probably can measure just a voltage on a normal diode).

This was the diode check on the meter.

Open circuit in both directions.

This one was ohmmeter input.

 

Best way to check D2 is in a circuit like this:

 

Best way to check D2 is in a circuit like this:
View attachment 308320

Unfortunately I don't have tools to test it like this right now.

I also find the polarity of the arrangement of the 12 volt supply odd.
Try this:
View attachment 308321

I can see that you just switched the order of the 12 volt supply and R5, C6 components. And increased value of R5.

I am still wondering what could destroy the circuit. If C6 blew first it could destroy the other components (D1, R5), but how could C6 blew first?

 

I am still wondering what could destroy the circuit. If C6 blew first it could destroy the other components (D1, R5), but how could C6 blew first?

Not sure unless a defective cap. What I don't understand is how all those caps C2-C5 are not destroyed also.
How does the dimmer function work?
Why not replace the mosfets with a SSR that can be controlled with 5 volts directly from the Arduino?

 

How does the dimmer function work?

I was inspired by this project: https://www.instructables.com/DIY-Trailing-Edge-Dimmer/ but when I used my dimmer, I set the mosfets to be fully on.

Why not replace the mosfets with a SSR that can be controlled with 5 volts directly from the Arduino?

That is a good idea, thank you.