How to fix a trailing edge dimmer?

Thread Starter

Vojtěch Tecl

Joined Oct 16, 2017
9
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.
 

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Thread Starter

Vojtěch Tecl

Joined Oct 16, 2017
9

sghioto

Joined Dec 31, 2017
5,369
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?
 
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Thread Starter

Vojtěch Tecl

Joined Oct 16, 2017
9
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.
 

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Thread Starter

Vojtěch Tecl

Joined Oct 16, 2017
9
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?
 

sghioto

Joined Dec 31, 2017
5,369
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?
1700863209489.png
 
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