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New SECA build thread

iansr

pfm Member
I am going to be building a pair of mono blocks using the latest iteration, V3.1, of Colin Wonfor’s SECA PCBs. I am aiming for the maximum output power of 40 wpc. I am currently getting quotes for toroids.

Each mono block will require a heatsink rated at 0.1 degrees C/W or better. That’s a huge amount of heat dissipation. My plan is to buy the heatsinks separately and then have a local metal fabricator make the enclosures incorporating the heatsinks. Perhaps I’m just lucky but there are lots of metal fabrication outfits in the West Riding.

Next week I am speaking to Julian Cavalot of BAL Group. He is their heatsink expert. Following that I will decide whether I am going to use just passive heating or incorporate a quiet slow speed fan into the chassis so that I can use a smaller heatsink.

I’ll post further updates as things progress.
 
I have put in the charity section some heatsinks that might be suitable. I used them for a Stan Curtis class a build.
 
So, just thinking about the fan option; I know MOSFETS have a maximum operating temperature, but I’m wondering if they have a minimum one, or an optimal temperature that is above normal room temperature? If i have a fan it is going to be running all the time so I’m wondering whether it will slow down the MOSFETS reaching ideal operating temperature?
 
So, just thinking about the fan option; I know MOSFETS have a maximum operating temperature, but I’m wondering if they have a minimum one, or an optimal temperature that is above normal room temperature? If i have a fan it is going to be running all the time so I’m wondering whether it will slow down the MOSFETS reaching ideal operating temperature?


For an IRF240 then maximum temp up to about 10 amps for maximum gain, I.e run as high temp as possible which suggest a smaller heatsink. I have a class A amplifier using silicon bipolar, the chip temp is above 100C, it’s reliable.
 
I like the large die and high temp working of the Power MOS FET. Problem are a pain, as Andy would Parrot Sick Oscillation, this amp is a source follower so as the current increase so does the Gate Source Voltage and the voltage drop across the Drain Source, you can get round this with the drive voltage being at least 10V higher than the main +V rail. Or to save cost use a bootstrap circuit, which is what this cct does.
The next problem is as FET get hotter the RDsON get higher so the heat goes up in a SECA circuit.
So I use large die, high power low RDsON, and big heatsinks and ceramic TO247 thermal pads.
 
Colin
I’ve done quite a bit of googling to find suitable heatsinks and there doesn’t seem to be many options given the 0.1 C/W target, and the ones I have found still end up being pretty damn big. Do you think I could get by with ones rated at 0.12?
 
Just a thought which already goes against your tall but narrow vision.
Could you use the sink in lid configuration with this design, 400mm2 would be far less huge that way.
 
Yes i did think about that, but they would take up more real estate that way. Aesthetically I think tall and thin will also be better, to my eyes at least.
 
Also - if used horizontally the heatsink will also be markedly less effective.
Nice idea, but not ideal when you need to shed so much heat.
 
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Spoke to some local metal fab shops today about getting some enclosures made. Now awaiting quotes.
 


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