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Registered Member #55
Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149
Seeing that my sale and trade thread is going somewhere different I might as well post a topic here.
If you run your DRSSTC at low duty cycles
How low? I have been having troubles with the to247 40n60s. The points where the leads connect to the copper PCB gets really hot after a minute or so of run time. The first time I did not build up the copper with enough solder and the trace exploded. Now with an appropriate amount of solder at the junction point I get localized heating of the T0247 case. I really wanted to make the to247 case work here, thats why I used a clamp type heatsink mounting and plenty of forced air. I will try copper plate instead of the tinned up clad board and see what happens. Here is a picture of the old fullbridge board. I think the copper is just too thin even with tons of solder clugged on it.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
First, you need to know the differences between a TO-247 package and a SOT-227 package. The only difference, given the same die (i.e. 40N60 IGBT), is the thermal impedance between the case and the junction, and also a greater surface area on the SOT-227 which gives a lesser thermal impedance between the case and the heatsink.
What this means, is that given the same operating conditions, there will a much greater temperature drop between the junction and the heatsink for the TO-247 device, as there is in the SOT-227.
And what this means, is that the heatsink must be kept that much cooler to ensure the junction temperature isn't exceeded.
That being said, if you are using TO-247's, you must have some pretty serious heatsink with a lot of fan cooling. The heatsink must be kept cool. Also, you need to use a thermal compound between the device and the heatsink. This is absolutely necessary.
Regarding duty cycle, you can maintain constant arc length and still reduce overall duty cycle (i.e. constant pulsewidth with decreasing PRF)
As duty cycle is directly related to heat dissipation, the temperature of the IGBT junctions will scale with the duty cycle.
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T0247 IGBT versus SOT-227 IGBT
