Loopy Transistor Study

1
Loopy Transistor Study
PNP Germanium Transistors from 1401 project. From
SMS card DHG (see last slide), identified as
having a slow fall time.
Test setup
2
Loopy Frequency Dependence
IV character versus scan rate when setting Ib
30 uA. Horizontal excursion is 0 to 4V, vertical
is 0 to 250uA.
20 KHz
5 KHz
500 Hz
50 Hz
5 Hz
DC - .125 Hz
3
Slow Speed Loop Details
Manual scan of Vce done with power supply knob (0
to 4V). Ib 30uA. Long persistence on storage
scope.
Scan from bottom to top in .5 seconds (Vce 0V to
4V)
Slow scan .125 Hz
Scan from top to bottom in .5 seconds (Vce 4V to
0V)
4
Slow Speed Loop Details
More manual scans of Vce done with power supply
knob (0 to 4V). Ib 30uA. Long persistence on
storage scope. Manual scans 5x faster than
previous slide.
Scan from bottom to top in .1 seconds (Vce 0V to
4V)
Scan from top to bottom in .1 seconds (Vce 4V to
0V)
5
Low Speed Loop Temperature Dependence
Transistor received a 1 second shot of circuit
cooler. Scan rate is 50 Hz. Total Vce excursion
is 4V.
Pre cooler curve
t150sec
t120sec
t90sec
t60sec
Increasing time Total elapsed about 2.5 mins
t30sec
t0sec
6
High Speed Loop Temperature Dependence
Transistor received a 1 second shot of circuit
cooler. Scan rate is 15KHz. Total Vce excursion
is 4V.
Pre cooler curve
t150sec
t120sec
t90sec
t60sec
Increasing time Total elapsed about 3 mins
t30sec
t0sec
7
Loopy Transistor Observations

• DC character is not loopy, although must get to
  very slow rates before this happens (4 seconds
  for 0 to 4 volt sweep)
• Increasing Vce curve is more normal than
  decreasing Vce curve. Decreasing Vce curve is
  flatter. Appears that the loop opens up
  starting at about .3 hz, with the increasing side
  dip dropping down, and the decreasing side dip
  moving up.
• Loopy behavior is highly temperature dependent.
• Loopy behavior is changes versus frequency.
  From DC to 20KHz, no loop behavior is seen from
  500Hz to 5KHz.

8
DHG SMS Card In 1401
Transistor Application Biased so always active