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1500 questions
21
votes
3 answers
Understanding USB Inrush Current Requirements
In relation to a previous question, I'm trying to understand the USB 2.0 requirements for inrush current. I understand the basic idea, but a few details are still unclear to me. The specification states, in part, that:
The maximum load (CRPB)…
David
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21
votes
2 answers
Why is Zener avalanche noise saw tooth shaped?
I have the following schematic of a Zener based noise source:-
simulate this circuit – Schematic created using CircuitLab
When built, an oscilloscope reveals a saw tooth noise signal at the "Noise" node, like:
The time base is 1us/div. Can anyone…
Paul Uszak
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21
votes
3 answers
What is the difference between SOT 23 and SOT 23-3 package types?
I am faced with two types of packaging:
SOT 23
SOT 23-3
Is there some difference between them?
Based an article in Wikipedia it seems like there are no differences.
KMM
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21
votes
1 answer
Difference between drill layer, hole layer, and milling layer in Eagle
What is the difference between the drill layer (44), the hole layer (45), and the milling layer (46) in Eagle PCB?
Alexis K
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21
votes
1 answer
Why is there a little nose on the PCIe connector?
PCI express cards have an edge connector with a little notch in it to prevent the card from moving if the socket is longer than the connector. Additionally, the printed circuit board has a protrusion in front of the actual connector. What is its…
FUZxxl
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21
votes
17 answers
How to 'fix' this in an enclosure without glueing?
I have an enclosure, and want to fix/put a STM32 inside, a relay and probably later a small circuit board.
However, the STM (STM32F103C8T6) and the relay do not have holes to fix them... and I do not want to glue them because maybe later I want to…
Michel Keijzers
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21
votes
1 answer
TO-92 not getting hot enough
I am controlling a DC fan by an AVR MCU and I am curious about the thermal characteristics of a 2N3904 NPN transistor over which the fan is connected.
Reading the transistor's datasheet, I find the following values:
$$
R_{\theta J-A} = 200\text{…
Nikola Malešević
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21
votes
2 answers
What might be the cause of high pitch sound coming from a switching regulator circuit?
We designed a switching regulator circuit using a 1.5MHz, internal-switch, switching regulator (semtech.com/images/datasheet/sc185.pdf). Vin is 5V, Vout is 3V3. We have an input capacitor (47uf), an output capacitor (47uf) and an inductor (1uH). The…
SomethingBetter
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21
votes
8 answers
How to deal with long chip lead times in small company
I am the chief engineer at a small company. Our product popularity is growing rapidly, and now we are learning about painful lead times for microcontrollers. The owner is demanding product overhauls to avoid distributor lead times. My question…
Zachary Scott Dickerson
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21
votes
4 answers
How to tell polarity expected of a DC barrel jack?
I'm sure this information is somewhere around the internet, but I can't find it.
I have a device that takes a DC barrel jack. I don't know the polarity it expects though. There is a marking though. It looks like this:
___
--- 12VDC
I'm 99% sure…
Earlz
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21
votes
12 answers
Does a diode really follow Ohm's Law?
Does a diode really follow Ohm's Law?
Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points.
Introducing the constant of proportionality, the resistance,one arrives at…
Gabriel Staples
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21
votes
2 answers
How do I use a transformer as an inductor?
Lp: Self inductance of the primary winding.
Ls: Self inductance of the secondary winding.
Lm: Mutual inductance between the primary and secondary windings.
Assume that I need an iron core inductor with large inductance to use under 50Hz or…
hkBattousai
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21
votes
6 answers
Why does this comparator not output a square wave?
I have a 4.43MHz sinusoidal output from an IC that I want to convert to a TTL square wave to use as a clock. The signal has a DC offset of around 2.5V and has an amplitude of about 0.5V peak to peak.
I attempted to convert this to a 0-5V square wave…
Batperson
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21
votes
6 answers
How to combat noise from my circuit polluting my 12V rail?
I made a controller for 12V DC fan. It is basically a buck DC-DC converter controlled by voltage. It regulates voltage for fan from 3V (lowest speed, fan draws 60mA @ 3V) to 12V (full speed, fan draws 240mA @ 12V). This controller works well, it…
Chupacabras
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21
votes
6 answers
Cell Phone as Microcontroller
I have a couple of cell phones laying around, one of them being this one:
http://www.gsmarena.com/sony_ericsson_elm-3057.php
Is possible to clear the flash memory and replace it with a bootloader and then upload arduino sketches or pic32…
Harry Svensson
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