[SOLVED] Question about pushbutton latch transistor operation

[d123]

Hi,

In the attached image, taken from:

https://www.daycounter.com/Circuits/Latching-Momentary-Switch/Latching-Momentary-Switch.phtml

I understand most of the theory of operation, except for: "(Q1 keeps Q2 turned on and) Q2 keeps Q3 turned on"

1) Why is it Q2 and not Q1 that keeps Q3 turned on?

"(When the switch is pulled low again,) the base of Q3 is tied to ground, because Q2 is on"

2) Why isn't the base of Q2 also pulled to ground at that moment, and why does Q1 base get pulled to ground because Q2 is on, rather than just because the pushbutton connects the base of Q1 to ground?

Thanks.



I think I've just understood the second question..., but the first makes no sense to me/don't understand what's happening for that to be so ("Q2 keeps Q3 turned on").

 

[d123]

I conclude that "...Q2 keeps Q3 turned on" is a mistake which should read: "Q1 keeps Q2 and Q3 turned on."

 

[KlausST]

Hi,

I didn´t go through the circuit in detail..
But i think:
* Q1 keeps Q3 turned ON
* Q2 generates the "toggle" feature.

Klaus