Activity for Circuit fantasist
| Type | On... | Excerpt | Status | Date |
|---|---|---|---|---|
| Comment | Post #279016 |
@tlfong01, I have uploaded the circuit of the light-to-voltage converter also for you - https://electrical.codidact.com/uploads/Ky66QamLX19NTN8CKxCnExUF. I had to dig a lot in my old archives to find it (that was 40 years ago). It is also interesting in itself but it has no direct connection with wh... (more) |
— | over 3 years ago |
| Comment | Post #279016 |
@coquelicot, I managed to find the light-to-voltage converting circuit scratched on a yellowed sheet of paper in 1982. I uploaded it especially for you:) I also added more explanations to make the text more clear. Just to note that these are details you should not stare at. Evaluate the inventive id... (more) |
— | over 3 years ago |
| Comment | Post #279022 |
And yet it is strange to talk about current gain here... Leaks are unpredictable. (more) |
— | over 3 years ago |
| Comment | Post #279030 |
Exactly... the DC mode is interesting here since the transistor transfer curve is nonlinear. (more) |
— | over 3 years ago |
| Comment | Post #279025 |
I agree with your considerations. Good find... (more) |
— | over 3 years ago |
| Comment | Post #279016 |
The difference between the potentiometer and the "single entry labeled 'light intensity signal'" is that the potentiometer is a real device... and the reader can see the path where the input current flows. For the purposes of understanding, it is very important to see where currents flow. That is why... (more) |
— | over 3 years ago |
| Comment | Post #279016 |
@coquelicot, To manually test a voltage-controlled analog circuit, you need a variable voltage source... but imagine you have only a constant one. Then, what else to use if not a simple potentiometer? I have outlined the studied circuit in yellow; the potentiometer (input voltage source) and the pow... (more) |
— | over 3 years ago |
| Comment | Post #279018 |
Good question... I have also asked myself this question... and I must admit I do not have a convincing answer. Maybe we should take a look at H&H and Student manual for H&H... (more) |
— | over 3 years ago |
| Comment | Post #279010 |
In the OP's circuit (NIC), I suppose there is a loop gain since the op-amp gain is enormous... although the total feedback ratio is a difference between the two voltage dividers ratios... (more) |
— | over 3 years ago |
| Comment | Post #279010 |
To work as a latch, we have to keep the input signal in a neutral state (in the middle of the hysteresis loop). Conversely, for it to be a Schmitt trigger, we must keep the input signal outside the hysteresis loop. (more) |
— | over 3 years ago |
| Comment | Post #279010 |
Every (op-amp) circuit with positive feedback and loop gain > 1 is a latch (with one input)... and every latch with one input has hysteresis. Depending on how we control it, it can work either as a latch or as a Schmitt trigger. (more) |
— | over 3 years ago |
| Comment | Post #279010 |
@Olin, first to move here my comment from below where I had put it wrong: If the four resistors were absolutely equal and the op-amp was ideal, the circuit would be identical as a bare op-amp without feedback (resistors). Now about your last comment above... (more) |
— | over 3 years ago |
| Comment | Post #279016 |
@tlfong01, the light-to-voltage converter is another circuit that stays before this. But it does not belong to this topic ("analog LED voltage indicator"). I have only mentioned it to make the story more human-friendly... (more) |
— | over 3 years ago |
| Comment | Post #279016 |
@tlfong01, to understand circuits you need more imagination than IQ (said Einstein)... (more) |
— | over 3 years ago |
| Comment | Post #279016 |
@Olin Lathrop, I need to think a lot before I answer you because I am quite surprised and I can not react. I just managed to ask myself the simple question, "Why are we so different?" (more) |
— | over 3 years ago |
| Comment | Post #279010 |
Olin, I understand you since the final result is an op-amp without any feedback, i.e., a "comparator without hysteresis". But actually there are two feedbacks (negative and positive) that neutralize each other and the final result is "no feedback". But this state is unstable - it is enough for the p... (more) |
— | over 3 years ago |
| Comment | Post #279010 |
@2kind, Thanks to your mistake you "invented" an ingenious circuit-:) This is how great inventions are sometimes made! (more) |
— | over 3 years ago |
| Comment | Post #279010 |
You have considered a very interesting situation in the OP's circuit when "left ends of R14 and R16 are tied to ground". Actually, this is a NIC. In this circuit, there are two kinds of feedback - negative (R16-R19) and positive (R14-R19). To be stable, this circuit requires the negative feedback to ... (more) |
— | over 3 years ago |
| Comment | Post #279010 |
You made me begin thinking about the "3-input diff amp"... It looks to me as a sort of a "summing-subtracting circuit". R3-R1 network is a passive voltage summer with weighted inputs. So Vp and Vref (0 V here since R1 is grounded) are summed according to the superposition principle - Vp.R1/(R1 + R3) ... (more) |
— | over 3 years ago |
| Comment | Post #279005 |
Indeed, I know there are applications where negative impedance converters (NIC) are used as amplifiers but I am not sure if this is the case here... Also, if the current is DC and it enters R6 from the left (as shown), the A1A output voltage should be negative. But the circuit is single-supplied only... (more) |
— | over 3 years ago |
| Comment | Post #279005 |
@2kind, It is a pleasure for me to think about such problems. Just to clarify that I have no special practical experience in this problem, I am just guided by a common sense. I think there is no need of TVS between the op-amp inputs since they are connected in series (through the ground) and this ne... (more) |
— | over 3 years ago |
| Comment | Post #279005 |
OK, there was some problem with edit... I have deleted the duplicate. (more) |
— | over 3 years ago |
| Comment | Post #278933 |
@tlfong01, Exactly! (1) is true... It is an unregulated power supply consisting of (a) + (b) + (c) cascaded... I frequently use the battery symbol to represent a voltage source... And (2) is completely true. I will write you a message later in the chat... (more) |
— | over 3 years ago |
| Comment | Post #278933 |
@tlfong01, Thanks for the attention to my humble "invention". "Bin is replaced by Bb" is said in the sense that, when the mains supply fails, already Bb but not Bin supplies the load. Bin stays at its place but it does not produce power (that is why it is drawn in light gray). (more) |
— | over 3 years ago |
| Comment | Post #278933 |
@tlfong01, BIN actually represents a diode rectifier (although it can be battery as well). The diodes inside this rectifier would be backward biased by the backup battery voltage Vb applied through the resistor R. Really, R will waste power... but what do we do? We can only decrease the difference b... (more) |
— | over 3 years ago |
| Comment | Post #278933 |
@tlfong01, Thanks for the response. It is strange why others keep silence... Browse the web for diode rectifiers (e.g., https://en.wikipedia.org/wiki/Diode_bridge) and you will see that, in this case, the diodes inside the rectifier are backward biased... and they stop the return current. (more) |
— | over 3 years ago |
| Comment | Post #278836 |
Just to clarify ... In inverting circuits, e.g. op-amp inverting amplifier with resistors R1, R2, the op-amp output acts as a negative resistor with "resistance" -R2. It neutralizes the positive resistance R2 and the result is virtual zero resistance (R2 - R2 = 0) aka "virtual ground". (more) |
— | over 3 years ago |
| Comment | Post #278933 |
... Also, R is high enough and the current and wasted power should be small. I am not a fan of calculations but I think R could be defined as follows: R = (Vin - Vb)/(Ich + IL/(beta+1)). (more) |
— | over 3 years ago |
| Comment | Post #278933 |
@tlfong01, Thanks for the response; it means a lot to me. I have conducted an interesting on-line exercise using various web resources including Codidact. We considered this story as an example of how a BJT can act as a diode. Bb means "backup battery". Bin is the input unregulated power supply. In ... (more) |
— | over 3 years ago |
| Comment | Post #278836 |
Regarding the thermistor with NTC, maybe you mean that its temperature increases when the current through it increases. As a result, its resistance decreases and the voltage drop across it decreases thus helping the input source. If so, it can act as a "differential negative resistor" if it does it ... (more) |
— | over 3 years ago |
| Comment | Post #278836 |
@tlfong01, The "true negative resistor" here is just a "dynamic voltage source" whose voltage is proportional to R (V = -I.R) and is added in series to the input voltage so that helps it. R is the original "positive" resistance that is converted to negative resistance by adding -2VR. The true negati... (more) |
— | over 3 years ago |
| Comment | Post #278933 |
@tlfong01, I will answer you but later because after a while I will have to start an online exercise with my favorite students on how to measure the diode IV curve. They are IT beginners and I will have to discuss exactly the questions you ask. If you don't mind, we will come in here and try to answe... (more) |
— | over 3 years ago |
| Comment | Post #278933 |
@coquelicot, You probably understand that here I wanted to show something more original than usual. BTW the input source may be weak since the alarm system does not normally consume much current. But when the bell turns on and consumption increases sharply, the backup battery turns on in parallel an... (more) |
— | over 3 years ago |
| Comment | Post #278933 |
@Olin Lathrop, I use simple conceptual circuits with a small number of generic elements. This allows me to use the rest of the space to visualize the invisible electrical quantities voltage and current. My goal is to reveal the idea and explain the circuit in order to deeply understand it. Some draw... (more) |
— | over 3 years ago |
| Comment | Post #278877 |
@coquelicot, OK, I have added it. Also, I have explained the connection between the button and the micro port. (more) |
— | over 3 years ago |
| Comment | Post #277844 |
Just to add that it is not a simple job to make a comparator with a differential input and a threshold because there are, in total, three input voltages. Two of them are single-ended (grounded) but the third (threshold voltage) is floating... and it must somehow be inserted in series with the others.... (more) |
— | over 3 years ago |
| Comment | Post #277844 |
A typical inventive solution with a scent of romance from the good old days… when simple but clever circuit tricks (Don Lancaster's "elegant simplicity") were appreciated… We can see two insights here: the first is a principle (relative instead of absolute threshold); the second is an implementation ... (more) |
— | over 3 years ago |
| Comment | Post #278760 |
I support the question and this kind of questions. I think that, in addition to specific questions, there should also be general questions. CoDidact will only benefit from this. (more) |
— | over 3 years ago |
| Comment | Post #278617 |
@coquelicot and LvW, Let's not bring here some not very good manners from other places. Let this be a good place where everything is done in the name of the great goal - UNDERSTANDING CIRCUITS. (more) |
— | over 3 years ago |
| Comment | Post #278636 |
I think that really, voltage is the cause and current is the effect... the voltage causes the current. Figuratively speaking, we can think of the voltage source as of a motor that drives the load through an "electrical transmission" (current). (more) |
— | over 3 years ago |
| Comment | Post #278637 |
I am not sure if this is the right name. I mean that "voltage-stable" = voltage-stabilizing = constant-voltage = voltage-type = diode IV curve... and the dual "current-stable" = current-stabilizing = constant-current = current-type = transistor output IV curve. The best combination is of two mutuall... (more) |
— | over 3 years ago |
| Comment | Post #278654 |
Thanks for the response. You made me think more about the technology of "self-answering questions". Perhaps the best option is to show one (your) possible answer and expect to receive more answers. But in any case, you have to signal to the others that you know some answer. (more) |
— | over 3 years ago |
| Comment | Post #278630 |
Interesting thoughts... BTW where can we see the "current control" in the circuit of a follower? (more) |
— | over 3 years ago |
| Comment | Post #278636 |
I completely support your observations about the difference between the physical and circuit view. Circuits need rather a kind of a "functional" than physical view. To understand circuits, we need to imagine what and how active devices do what they do... we have to imagine the circuit operation. It i... (more) |
— | over 3 years ago |
| Comment | Post #278636 |
Incredibly beautifully written ... it was a real pleasure for me to read it. I am not a professional circuit designer but the observations I have from my practical experience and a lot of reasoning make me support this opinion. To avoid the "war" between current and voltage, I would offer the followi... (more) |
— | over 3 years ago |
| Comment | Post #278613 |
So, we can simply say that it behaves as an "ideal" (perfect, constant, steady) voltage source? (more) |
— | over 3 years ago |
| Comment | Post #278604 |
… The upper (Vdd) sources current to this point thus trying to increase its voltage and the lower (ground) sinks current from it thus trying to decrease it. As though, the two sources "pull" the common point in opposite directions - up and down… (I will finish my response later since now I have to go... (more) |
— | over 3 years ago |
| Comment | Post #278604 |
… Most electronic circuits (probably > 90%) are based on this humble network of two elements in series supplied by a voltage source… because they handle voltage; the old voltage divider is the simplest example. Besides this classic viewpoint, we can think of it also as of two voltage sources (the one... (more) |
— | over 3 years ago |
| Comment | Post #278604 |
@coquelicot, Thanks for the sincerity. People like you make me drop everything else and try to explain the philosophy of things to them... but it takes time and room…and not bother me with "no discussion" warnings. Usually, I richly illustrate my answers but here I assumed that everyone knows what... (more) |
— | over 3 years ago |
| Comment | Post #278582 |
Olin, Perfectly and comprehensively written answer (like a paper) which was necessary not only for me but also for the meta section! I need time to realize it. But I think the question was also well formulated:) I feel sympathy for your endeavor because I have started initiatives all my life. Here is... (more) |
— | over 3 years ago |
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