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Accepted

What's the intuition for reading transistor/resistor circuits?

What's a step by step way of thinking about the flow of electrons in such a circuit? How can we tell it would provide constant current for instance? The first step is to forget about flow of ...
• 176k
Accepted

op amp+mosfet = current source.Why do we need a feedback resistor?

R2 (10k R4 in my diagram) is there to form together with C1 (1nF capacitor) a Miller Integrator to prevent unwanted oscillation. And yes, this circuit will sometimes oscillate, mainly due to poor PCB/...
• 14.9k
Accepted

What are some practical examples of a constant current source?

Photovoltaic cells and betavoltaic cells are examples of devices that produce more-or-less constant current up to some maximum open-circuit voltage, just as a battery produces more-or-less constant ...
• 402k

Why are current sources not drawn explicitly in the datasheets' schematic diagrams?

Most likely just to simplify the schematic. They would likely be implemented with various scaled and interconnected current mirrors as well as some sort of reference current generation circuit. One ...
• 41.2k

How do we create current sources?

Constant current sources ... there are no such devices in nature; almost all of sources are (constant) voltage sources. So we have to make them. I think you are correct. Due to physics chemical ...
• 176k

What's the intuition for reading transistor/resistor circuits?

What's the intuition for reading transistor/resistor circuits? More precisely speaking, "reading" means "understanding" here. So, the question is, "How do we intuitively ...
• 17.1k

Reversed DIP Switch

This is what your circuit looks like: simulate this circuit – Schematic created using CircuitLab When you close the DIPSW the LED will be shorted thus the current will flow through the DIPSW ...
• 35.3k
Accepted

I don't understand current source, voltage source, infinite resistance, zero resistance etc

If something has infinite resistance wouldn't nothing happen because everything is blocked? I also don't understand what an "open circuit" really means (to my eye it just looks like a ...
• 56.8k

Why do PNP transistors source current and NPN transistors sink it?

Have you ever heard of an emitter follower? An NPN transistor connected in the emitter follower configuration sources current: This figure is from the Wikipedia page on the common collector (emitter ...
• 71.9k
Accepted

Why do I get two different answers for the current through the 47 kΩ resistor when I do a source transformation?

If you transform a source and a resistor then the only equivalence is the V/I characteristics at the two terminals of the transformed circuit, not for the elements inside the transformed circuit. If ...
• 31.6k

op amp+mosfet = current source.Why do we need a feedback resistor?

You don't need a feedback resistor and neither do you need C1. I guess the "designer" has some strange perception that the circuit will oscillate without them but it won't. Oscillation will occur if ...
• 460k
Accepted

Tube cathode biasing with CCS

The 12AX7 double triode is connected as a differential amplifier (long-tailed pair). In the Wikipedia article you see a similar circuit implemented with BJTs, but the principle is the same: consider ...
Accepted

Why is my transistor beta lower than expected?

The beta value you are getting is rather typical for a transistor in reverse active mode. That is, using the collector as an emitter. Assuming every thing else is ok (vendor, supplier, and ...
• 8,446

How can I make a current source that can supply 1uA?

D2 generates a stable voltage, while the forward voltage of Q1 varies with temperature (by about -2 mV/deg. C). You can compensate for this by putting a standard diode in series with D2 -- e.g. a ...
• 402k

Why do I get two different answers for the current through the 47 kΩ resistor when I do a source transformation?

I gather you find the correct answer from this transformation: simulate this circuit – Schematic created using CircuitLab One way to see why is that the transformation on the left side doesn't ...
• 78.1k

Sensor datasheet shows op-amp circuit with capacitor to ground from inverting input. How does this work?

If you're referring to the 2.2 μF cap, it was probably placed for the purpose of not amplifying a DC signal (including the op-amp's own offset). Think about it: at DC, that capacitor is an open, ...
• 4,175
Accepted

How do I explain this regulation action in terms of control theory?

There is no closed loop feedback system evident That's because you didn't spot it. It's the base-emitter region of the 2N3904 (Q2) that acts like a comparator at around 0.5 volts to 0.7 volts (...
• 460k
Accepted

Practical example of controlled voltage and current sources

Short answer The difference between the ordinary constant sources and dependent sources is that the former have only output (the input is implicit, constant) while the latter have both input and ...
• 17.1k
Accepted

PIC Micro - Can I use both sinking and sourcing maximum current ratings if some pins sink while others source?

The maximum ratings are usually about two things, broadly speaking. One is about local dissipation -- the port pins are often arranged near each other on the die and if you dissipate too much in a ...
• 78.1k
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• 4,279