I recently performed a experiment on a voltage divider network as a front end to establish a small base biasing voltage. Placing a R1 as the resistor connected to the -Vcc, (for a PnP-pn2907 as Q1) and the base of Q1.Also the R2 was placed between the base and ground (which is positive in this case.
The frist set of resistors is used for R1 and R2 is,R1 is one meg. ohms' and R2 220k ohms for the Q1 base bias. the collectro resistor (VRC is 1k ohms.VR2 as the base voltage is about .55 volts. IB=12.1 micro-amps. Ic=1 miliamps.VR1=15.5 volts.VCE=13.5 volts.VRC=2.7 volts.
The second expertment is the same config grounded emitter directly to groundZ) a RC=1ooo ohms. The voltage divider is changed to R1=100k ohms and R2 (from base to ground)=220k ohms.According to the voltage divider formula there should be enough voltage across the base to be registered on the Volt Meter. Which says that the base is about 0.5 or 0.6 volts. VR1=14.5 volts. VR2=0.5 or 0.6 volt on the meter.VRC=11.4 volts
In all serveral cases the bases seems to be locked to 0.5 or 0.6 volts and the R1's that is connected to -Vcc is almost carrying the whole -Vcc supply in each different rearrangement of the voltage divider network input circuits.
What happen to the base voltage drop across the Rb1 ?
Where is the Votage for the base ?
The frist set of resistors is used for R1 and R2 is,R1 is one meg. ohms' and R2 220k ohms for the Q1 base bias. the collectro resistor (VRC is 1k ohms.VR2 as the base voltage is about .55 volts. IB=12.1 micro-amps. Ic=1 miliamps.VR1=15.5 volts.VCE=13.5 volts.VRC=2.7 volts.
The second expertment is the same config grounded emitter directly to groundZ) a RC=1ooo ohms. The voltage divider is changed to R1=100k ohms and R2 (from base to ground)=220k ohms.According to the voltage divider formula there should be enough voltage across the base to be registered on the Volt Meter. Which says that the base is about 0.5 or 0.6 volts. VR1=14.5 volts. VR2=0.5 or 0.6 volt on the meter.VRC=11.4 volts
In all serveral cases the bases seems to be locked to 0.5 or 0.6 volts and the R1's that is connected to -Vcc is almost carrying the whole -Vcc supply in each different rearrangement of the voltage divider network input circuits.
What happen to the base voltage drop across the Rb1 ?
Where is the Votage for the base ?