Part D: DC Biasing with DC Feedback
Students may notice that the collector current (Ic) in part C varies among groups. The variation is caused by the instability nature of the current gain of the BJT. This variation of collector current can be reduced by introducing a DC feedback into the circuit. To allow the feedback mechanism works efficiently, a voltage divider circuit is used to provide vBB and RBB.
1. Construct a circuit as shown in Figure 10.
a. R1= 56 K, R2 = 20 K, RC = 10 K, and RE = 2.2 K. RE in the above circuit is the DC feedback resistor.
b. V1 is output from the 5 VDC power supply from part B.
2. Determine value of IB and IC from voltages across R1 and RC respectively. The values of R used in the calculation should be taken from the direct measurement.
3. Note your base current (IB) and collector current (IC).
4. Submit this value to the TA. In the report students should make a discussion about the obtained collector current among groups
The circuit in part d will be used again in the next experiment