Hello,
Attached is a portion of an example Ron made for me. I understand the general idea that turning Q6 on will turn Q4 off. Or, as Ron put it:
"When Q6 is saturated (Vce≈0.1V), it steals the base current from Q4. Q4 cannot be ON unless the base voltage ≈0.7V."
Now, if I want to add an LED with a voltage drop of 1.8 at point "A", I'm confused about how to calculate the values for R6 and R7 such that Q4 will be either saturated or off.
Using a meter and trial & error, I came up with an R7 of 150k and R6 of 1.8k. However, I'm missing how to reverse engineer that and determine my values mathematically beforehand.
How's that work?
(Thank you),
-masked
Attached is a portion of an example Ron made for me. I understand the general idea that turning Q6 on will turn Q4 off. Or, as Ron put it:
"When Q6 is saturated (Vce≈0.1V), it steals the base current from Q4. Q4 cannot be ON unless the base voltage ≈0.7V."
Now, if I want to add an LED with a voltage drop of 1.8 at point "A", I'm confused about how to calculate the values for R6 and R7 such that Q4 will be either saturated or off.
Using a meter and trial & error, I came up with an R7 of 150k and R6 of 1.8k. However, I'm missing how to reverse engineer that and determine my values mathematically beforehand.
How's that work?
(Thank you),
-masked
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