BJT PNP Switch: Why Vee Must Reach Zero for On

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In a BJT PNP switch, the base voltage does not need to reach zero to turn it on; it must be sufficiently negative relative to the emitter to forward bias the base-emitter junction. For a Vee of 5V, the base must be at least 4.3V (5V - 0.7V) to achieve this. Simulations confirm that the switch operates correctly under these conditions. Additionally, there is a noted difference in VCE saturation between PNP and NPN transistors, with PNP typically exhibiting lower saturation voltage in certain applications like voltage regulators. Understanding these principles is crucial for effective circuit design.
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In a BJT PNP switch, why does the base voltage need to go to zero to turn it on.
If Vee is 5V, the base has to be 5-0.7v to make the BE fwd biased.
 
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"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.
 
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.

Great. I just simulated it, it works.
Did the same thing last week, damn thing didn't work. That's why I doubted my understanding.

The reason I started with PNP switch is bcoz I don't understand why the VCE sat of PNP pass transistor (in voltage regulator) is much less than NPN Vce sat.
 

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