48
votes
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 ...
- 180k
20
votes
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 ...
17
votes
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 ...
- 41.6k
14
votes
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 ...
- 180k
14
votes
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 ...
- 19.4k
13
votes
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 ...
- 38.5k
13
votes
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 ...
- 57.3k
13
votes
What type of input is required by a gate driver? The data sheet says 50 A
This kind of nonsense is common as companies and their products are acquired and divested. Those parts were originally made by Unitrode. Below is a snippet from an archived Unitrode datasheet:
So the ...
13
votes
What does the circuit shown in the picture do?
Searching for something familiar
If we tidy up this mess of resistors and op-amps a bit, we can recognize the so-called "improved Howland current source". The idea behind this famous circuit ...
- 19.4k
12
votes
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 ...
- 73.5k
11
votes
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 ...
- 31.7k
10
votes
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 ...
10
votes
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 ...
- 8,546
10
votes
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 ...
10
votes
Accepted
Why do PNP transistors source current and NPN transistors sink it?
This is because it's more typical to connect the load to the collector. You can use the emitter as an output, but that has certain limitations...the voltage gain will always be 1 in an analog emitter ...
10
votes
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 ...
- 78.7k
10
votes
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, ...
- 4,708
10
votes
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 (...
- 473k
10
votes
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 ...
- 19.4k
10
votes
What does the circuit shown in the picture do?
This is a current source for a Platinum Resistance Thermometer known to be more linear and stable than thermocouples.
The interface indicates a PT100 is used which is 100 ohms at 0°C. The US std. is 0....
- 148k
10
votes
Voltage controlled current source design
This design is unsuited for your application (high voltage/low current) as it is made for a low voltage/high current application, not yours.
I suggest you might want to adapt a TI reference design, ...
9
votes
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 ...
- 78.7k
9
votes
Accepted
LM317 intermittent current source
To drive 50 mA through 330 ohms, you need 16.5 V.
For 50 mA through 1330 ohms you need 66.5 V.
In the constant current mode, the maximum output voltage of the LM317 circuit is \$V_{in} - 3\ {\rm V} ...
- 134k
9
votes
Accepted
How do we create current sources?
I will expose my philosophy in a few consecutive steps each of them illustrated by a colorful picture. The left part a is a conceptual electrical circuit illustrating the basic idea; the right part b ...
- 19.4k
9
votes
Accepted
How to reach ~50nA p-p current noise in ~200mA current source?
The main theme is: eliminate sources of 1/f as far as possible and limit bandwidth as desired. I suggest the following principal circuit (details added further down):
Low Noise Resistor
The main ...
- 23.4k
9
votes
Accepted
Question about electrical power in circuits
By example I can demonstrate how a current source can both absorb and emit energy. Take this simple circuit consisting of a single voltage source (a battery) and a resistor:
simulate this circuit &...
- 47k
9
votes
Accepted
Current source with MOSFET
In my understanding the 1K along with the 200pF create an integrator
topology to provide some stability
Correct and, particularly when using a MOSFET in these configurations there can be a ...
- 473k
9
votes
Passing 10 A through a nichrome wire (2.3 Ω) with a 4.2 V Li-ion battery source
There is nothing to figure out, because it is not possible.
A 2.3 ohm load on a 4.2 V battery will draw a current of 1.8 A.
And the battery is almost never that full to have 4.2 V, typical battery has ...
- 172k
9
votes
Why is current across a voltage source considered in circuit analysis but not voltage across a current source?
I'm not sure why you think KCL concerns itself with voltages anywhere, or KVL somehow needs to know anything about current anywhere. When applying KCL, we consider only current. When applying KVL, we ...
- 47k
8
votes
Accepted
How does the resistor at the tail act as a current source in a differential pair?
An ideal current source has infinite output impedance (i.e. \$dV/dI = \infty\$). A real current source is equivalent to an ideal current source in parallel with some finite output impedance Ro.
A ...
- 4,309
Only top scored, non community-wiki answers of a minimum length are eligible