Pulse and Digital Circuits

6.5 BREAKDOWN VOLTAGES

We have seen that by the application of a signal of proper polarity and magnitude, a transistor switch can be driven into saturation. As a result, the voltage at the collector of the device is V_CE(sat) (typically 0.1 V for Ge and 0.2 V for Si). Now, when a signal of opposite polarity is applied as input to the switch, ideally the voltage at the collector rises to V_CC. Thus, we see that the change in voltage at the collector is V_CC − V_CE(sat) ≈ V_CC. This output is connected to operate some other circuits. For proper operation, it is desirable that V_CC be made reasonably large. However, by increasing the value of V_CC, the reverse-bias voltage on the collector base diode could become so large that an avalanche breakdown may ...