Help: Opamp Comparator Circuit

[ericgibbs]

no its not for homework, but i understand thanks.

hi,
For reference, although the 13.4V zener will start to conduct at slightly over 13.4V, the current thru R8 will not create a voltage drop large enough to forward bias the Q3 base, so it will not switch on.

As the current thru the 13.4v zener path increases due an increasing V1 more current will flow and the voltage across R8 will reach about 0.7V , at which point Q3 will start conducting.

Is this any clearer.?

 

[neoshinzo]

yes i was noticing that, thanks for explaining.

 

[neoshinzo]

hi,
For reference, although the 13.4V zener will start to conduct at slightly over 13.4V, the current thru R8 will not create a voltage drop large enough to forward bias the Q3 base, so it will not switch on.

As the current thru the 13.4v zener path increases due an increasing V1 more current will flow and the voltage across R8 will reach about 0.7V , at which point Q3 will start conducting.

Is this any clearer.?

hi, is this the same reason why Q1 gets turn on? even though V1 is 11.5V when its supposed to be less than 11.4V of D4,5,6 voltage to switch off Q2 and switch on Q1?

 

[ericgibbs]

hi, is this the same reason why Q1 gets turn on? even though V1 is 11.5V when its supposed to be less than 11.4V of D4,5,6 voltage to switch off Q2 and switch on Q1?

hi,
The D6 zener chain has a voltage drop of 11.4V, Q2 requires a voltage across R5 of about +0.7V to turn it ON, so in effect V1 has to about 11.4V + 0.7V before Q2 is fully ON.

Only when Q2 is fully ON will Q1 be OFF.

With this type of circuit its accuracy in switching at the required points depends upon many factors.
eg: zener voltage tolerances, diode conduction voltages, transistor Vbe turn ON voltages [can be +0.65v]

Its basically a voltage indicator circuit, not a precise voltage measuring circuit.

Does this explain it OK.?

 

[sheng_james]

hi

hey guys, i was hoping someone could help me to understand how the below circuit works. i understand the operating principle, but i wanted to know what the parts do and how i can analyze it mathematically. i'm not an electronics student, i'm just playing around with multisim and i have read through some of my older brother's electronics text books.

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View attachment 18632

hey can i know what version did u use in your schematic?
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