Gas station without pumps

2017 May 16

New problem in class-D lab

Filed under: Circuits course — gasstationwithoutpumps @ 22:37
Tags: , , ,

Today was the last day for the class-D power amplifier lab, and the students had a problem that we’d never encountered before—the breadboards kept squirting the nFETs out of the breadboard (sometimes the landed several inches away).

We were using the same nFETs as last year,NTD4858N, which comes in a TO-251-3 Stub Leads (which they call IPak) package.  The problem is that this year’s breadboards have their contact springs deeper than in previous years, so the stub leads barely reach them.  I don’t know whether the breadboards were ordered from the supplier I had found (http://www.meerkatsystems.net/html/10000023.html) or whether they substituted one from one of their favorite suppliers.  It would be good to know, as this year’s breadboards seem to be inferior to previous year’s.

Next year, I think I’ll specify the nFET to be PSMN022-30PL,127, which comes in a TO-220 package and sits more firmly in the breadboard.

Tomorrow I’m giving a quiz in class—something I try to avoid doing, but so many students have not been showing up for class nor turning in the required pre-lab homework that I was compelled to assess them some other way.  My guess is that the grade distribution will be similar to the distribution for the sum of the homework so far (out of 50 possible points):

 1.0  1
 1.5  2
 2.5  1
 3.0  1
 3.5  3
 4.5  1
 5.0  1
 5.5  1
 6.0  1
 7.0  3
 7.5  2
 8.5  5
 9.0  1
 9.5  4
10.0  4
11.0  1
11.5  2
12.0  3
12.5  4
13.0  1
14.0  1
14.5  1
15.0  1
16.0  3
16.5  2
17.0  2
19.0  2
19.5  1
20.0  1
20.5  1
21.5  2
24.0  1
25.5  1
26.0  1
27.0  1
28.0  1
28.5  1
30.5  1
31.5  1
36.5  1

I further conjecture that there will be a very high correlation of scores (so I won’t really learn all that much about the students). But I’m prepared to be surprised—I made the quiz deliberately fairly easy, so it is possible that students who have struggled with the design problems of the homework may be able to do the quiz.

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