Electric OU: Tar Baby / NERD Circuit MOSFET Stress Test
The IRFPG50 is one tough transistor.
Erratum: The duty cycle changed when I changed the range setting on the FG, and did not preserve the approx. 20 percent I had dialed in. Instead the ON duty cycle during the actual experimental run looks to be more like 30 percent. Sorry about that, looks like the F43 might need some replacement timing caps.
The test is still valid though….. it turns out that wire connection failure is another possibility to explain the Figure 3 scopeshot ! Electronic tin/lead solder melts at a temperature between 180 and 190 C, and Tar Baby’s mosfet exceeded that early on in the test.
Tar Baby’s socketed connectors cannot fail unless they actually melt down, but Ainslie’s soldered wires would melt and loosen and come off the leads when the mosfet got to the temperatures I’ve seen here. Still perfectly functional at over 200 C, but a soldered lead wire would definitely come loose and open the connection just like a failed mosfet would.
Perhaps the loose wire was noticed the next day, repaired as a matter of course and forgotten about, but the mosfet could still be perfectly fine, and as long as it never gets that hot again (never uses six batteries again), no more failures would occur.
And the Fig 3 scopeshot would result from the one failure at over 75 volts input.