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

Loopy Frequency Dependence

IV character versus scan rate when setting Ib = 30 uA. Horizontal excursion is 0 to 4V, vertical is 0 to 250uA.

‘DC’ - .125 Hz

5 Hz

50 Hz

500 Hz

5 KHz

20 KHz

Slow Speed Loop Details

Manual scan of Vce done with power supply knob (0 to 4V). Ib = 30uA. Long persistence on storage scope.

Slow scan .125 HzScan from top to bottom in .5 seconds (Vce 4V to 0V)

Scan from bottom to top in .5 seconds (Vce 0V to 4V)

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 top to bottom in .1 seconds (Vce 4V to 0V)

Scan from bottom to top in .1 seconds (Vce 0V to 4V)

Low Speed Loop Temperature Dependence

Transistor received a 1 second shot of circuit cooler. Scan rate is 50 Hz. Total Vce excursion is 4V.

Increasing time Total elapsed about 2.5 mins

Pre cooler curve

t=0sec

t=30sec

t=60sec

t=90sec

t=120sec

t=150sec

High Speed Loop Temperature Dependence

Transistor received a 1 second shot of circuit cooler. Scan rate is 15KHz. Total Vce excursion is 4V.

Increasing time Total elapsed about 3 mins

Pre cooler curve

t=0sec

t=30sec

t=60sec

t=90sec

t=120sec

t=150sec

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.

DHG SMS Card In 1401

Transistor ApplicationBiased so always active