1. Transistor Switching Networks, Troubleshooting, pnp networks and Bias Stabilization

2. Transistor Switching Networks
Transistors with only the DC source applied can be used as electronic switches.

3. Switching Circuit Calculations
Saturation current:
To ensure saturation:
Emitter-collector resistance at saturation and cutoff:

4. Switching Time Transistor switching times:
For general purpose transistor, we find:
ts = 120 ns
td = 25 ns
tr = 13 ns
tf = 12 ns
Therefore:
ton = 38 ns
toff = 132 ns

5. Troubleshooting Hints
Approximate voltages
VBE  .7 V for silicon transistors
VCE  25% to 75% of VCC
Test for opens and shorts with an ohmmeter.
Test the solder joints.
Test the transistor with a transistor tester or a curve tracer.
Note that the load or the next stage affects the transistor operation.

6. PNP Transistors
The analysis for pnp transistor biasing circuits is the same as that for npn transistor circuits. The only difference is that the currents are flowing in the opposite direction.

7. BIAS STABILIZATION
is a measure of the sensitivity of a network to variations in its parameters
β (beta): increases with increase in temperature
|VBE|: decreases about 2.5 mV per degree Celsius (oC) increase in temperature
ICO (reverse saturation current): doubles in value in every 10 oC increase in temperature