single-, two-, and four-quadrant switches

Hi,

I was reading up on quadrant switches and need your with some points.

I was using this text: **broken link removed**
(or, use Google drive PDF: https://drive.google.com/file/d/168CHus1Rzm4fCViEJdFnOA845f_R3PsN/view?usp=sharing)

Question 1:
In Slide #8 it says that a BJT is single quadrant switch which can block positive off-state voltage. Does it mean a BJT cannot block negative voltage? The shown BJT is an NPN. In Slide #19 it shows how an NPN could function as a two quadrant switch. Doesn't it suggest that a NPN cannot block negative voltage on its own? Where am I going wrong?

Slide #8:



Slide #19:
(edited after rjenkinsgb post to substitute the correct slide; previously this slide was mistakenly used)



Question 2:
Yes, the body diode won't conduct but the diode in yellow would definitely conduct reverse current. So, what's the purpose of bypassing body diode?

Slide #14:




Note to self:
Slides related to quadrant switched end around slide #23.
Related video, possibly by the author of slides: watch?)v=GLdMUd27LtM (insert www.youtube.com/ at the front)

PG1995 said:

In Slide #19 it shows how an NPN could function as a two quadrant switch

Click to expand...

Slide 19 shows a MOSFET, not an NPN transistor; they have very different characteristics.

rjenkinsgb said:

Slide 19 shows a MOSFET, not an NPN transistor; they have very different characteristics.

Click to expand...

I'm sorry about the confusion. I will edit the original post too.

Slide #19:

PG1995 said:

Doesn't it suggest that a NPN cannot block negative voltage on its own? Where am I going wrong?

Click to expand...

Back to the original question:

If you reverse the voltage across a bipolar transistor, current would flow through the collector-base junction as if it's just a simple diode. An external series diode prevents that.

Thank you.

I get your point.