uart said:"In a BJT PNP switch, why does the base voltage need to go to zero to turn it on." - It doesn't
"If Vee is 5V, the base has to be 5-0.7v to make the BE fwd biased" - Correct.
Vee, or the voltage at the emitter of a BJT PNP transistor, needs to reach zero in order for the transistor to turn on because this is the point at which the base-emitter junction becomes forward biased. When the base-emitter junction is forward biased, the transistor can conduct current and act as a switch.
If Vee does not reach zero, the base-emitter junction of the BJT PNP transistor will not become forward biased. This means that the transistor will not be able to conduct current and therefore will not turn on. The switch will remain in the off state.
Vee can be controlled through the use of a voltage source, such as a battery or power supply, connected to the emitter terminal of the transistor. By adjusting the voltage of this source, the Vee can be varied and the transistor can be turned on or off.
Yes, Vee must reach a specific voltage known as the forward bias voltage for the base-emitter junction in order for the BJT PNP switch to turn on. This voltage varies depending on the specific transistor being used and can typically range from 0.6-0.7 volts.
Yes, Vee can reach a negative voltage in a BJT PNP switch. However, in order for the transistor to turn on, the base-emitter junction must still be forward biased. This means that the negative voltage must be applied to the base terminal, while the emitter terminal must be at a lower voltage, typically 0V.