I’ve been told that these transistors, the MJL and the NJW, have the same die just the NJW being a smaller case. So given the idea that they would be mounted to the same heatsink that would adequately pull the heat from them, is there any reason to go for the MJL over the NJW? Would the NJW devices do equally well and remain at a safe temp?
Vs
(Not the exact transistors, just using for size reference).
While both hang off of the edge slightly the NJW obviously have a higher percentage of the body making contact with the heatsink, but nearly all of the metal tab on both are making contact. The originals hung over as well. With both transistors having the same dissipation, I’m just curious what the benefits of the bigger case are. Holes are drilled and tapped in that location to get best coverage of the transistor to heatsink contact.
Thank you,
Dan
Vs
(Not the exact transistors, just using for size reference).
While both hang off of the edge slightly the NJW obviously have a higher percentage of the body making contact with the heatsink, but nearly all of the metal tab on both are making contact. The originals hung over as well. With both transistors having the same dissipation, I’m just curious what the benefits of the bigger case are. Holes are drilled and tapped in that location to get best coverage of the transistor to heatsink contact.
Thank you,
Dan
The best heat transfer is going to be to mount them on the large flat side, NOT the edge.
The only difference between the two is the contact area from the heat spreader to heat sink. If you mount them as proposed, there is NO advantage to the larger MJL devices.
You could use the original holes, and mount the devices with bar clamps instead of the new tapped holes. That would have been easier - one broken tap and your heatsink is toast. Pressure over the center where the die actually is is better than the one mounting hole at the top anyway.
The only difference between the two is the contact area from the heat spreader to heat sink. If you mount them as proposed, there is NO advantage to the larger MJL devices.
You could use the original holes, and mount the devices with bar clamps instead of the new tapped holes. That would have been easier - one broken tap and your heatsink is toast. Pressure over the center where the die actually is is better than the one mounting hole at the top anyway.
I 100% agree. I wanted to originally mount the transistors like this:
but then the leads would be reversed to the orientation of the driver board so I would need flying leads from the transistor legs so I could swap them around. The biggest issue though was that the screw that would mount the transistor would be pretty much touching the back of the driver board once it’s mounted to the stand-offs you see coming from the heatsink. The original transistors were mounted on the bottom as well, I’m guessing for this same reason? Ideally the driver board would have holes you could reach through to tighten and loosen the transistor screws.
And yes, I have already realized that lol, if I could do it over again I wouldn’t have drilled and tapped the screws, I’d just clamp them using the original screw holes. I still may since I’d have to drill out the other heatsink still and manufacturing small clamping bars seem like a better option.
Being that they use the same die, I wonder how effective the larger heat spreader on the TO-264 really is. Meaning if you didn’t worry mica insulators, but just mounted a single transistor of each type to it’s own isolated heatsink that was more than big enough, just a very thin layer of Dowsil 340 between the transistor and heatsink, how much cooler would the TO-264 really be? And even with a mica insulator between, how much cooler would the larger transistor be given that all other parameters (voltage, current, output, ext) are equal. The extra surface area of the larger transistor isn’t a huge amount.
Dan