wrote:
On Monday, November 23, 2020 at 3:50:47 PM UTC-5, Chuck wrote:
Well, I have one additional so called "30 amp" Chinese dimmer remaining
after the prior one smoked. This one had a circuit breaker and it did
go today, but not before it started smoking. As I said, I have a good
Astron power supply on the way to replace, but I still had the dimmer in
place until then and outdoors.

This time, I decided to open it up and see what's going on. As others
have said, the Chinese tend to exaggerate ratings so "30 amp" was
probably far from it, but I was surprised what I saw internally:

two HY1707 Mosfets
an LM358
a 78L05
a 555 timer

non inductor ???


At 12V, 7 amp load, it seems like it should have been able to handle the
load, but I am wondering that since I was driving it with a switching
supply, maybe that somehow affected the dimmer? By the way, the burnout
was one of the HY1707's. Perhaps they actually need a heatsink instead
of just being attached to the circuit board?

That's absolutely all for the Chinese stuff. I had a constant voltage/
current module on the way, but not even going to open it. Can't trust
it anymore.

A device like that needs a proper heatsink. Even if the metal tab is soldered to the PC it's still inadequate for high power applications.


For 70A mosfet 7A is light load. Estimate based on typical
values shows that it should disspate about 0.3W. For TO-220
part at that load heatsink makes little economic sense: mosfet
will run fine without heatsink and better (lower Rdson)
mosfet is cheaper than heatsink. Of course, if one wants
to handle nominal 30A, than heatsink would be necessary.

The above assumed that there is an inductor and that second
HY1707 works as synchronous rectifier. Otherwise RMS current
may be much larger than average.

--
Waldek Hebisch