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1500 questions
30
votes
3 answers
What killed these X2 caps?
A few years ago, I designed an MCU-controlled dimmer driving a 150W mains halogen lamp. This is in Western Europe; 50Hz 230VAC. It uses X2-rated capacitors as capacitive droppers for the power supply, and another X2-rated capacitor for interference…
marcelm
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30
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2 answers
How to disable a single op-amp in dual packaging?
I am using a dual op-amp package in a circuit, however I only need to use one. Is there anyway to disable the other op-amp so it doesn't inject electrical noise in my circuitboard? I think grounding the positive input and setting the op-amp into…
user1207381
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30
votes
5 answers
Why are inferred latches bad?
My compiler complains about inferred latches in my combinatorial loops (always @(*), in Verilog). I was also told that inferred latches should preferably be avoided.
What exactly is wrong with inferred latches? They certainly make combinatorial…
Randomblue
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30
votes
5 answers
Common types of diodes to keep around
I'm working on stocking my home workshop with frequently used parts so I can spend more time tinkering and less time watching my mailbox.
What are the differences between different kinds of diodes? I've seen schottky, zenner, signal, and rectifier…
Grant
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30
votes
9 answers
Blink an LED with just a capacitor?
Is it possible to blink an LED using just a capacitor? (and maybe a resistor).
For example, if I want to LED to blink once every 2 seconds. Is that possible?
I know it can be done with a 555 as well as with a capacitor and transistor.
mesh
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30
votes
7 answers
Why aren't CPUs cooled from below as well as above?
The transistory bits of an integrated circuit are approximately in the centre of the (plastic or ceramic) package. They sometimes get hot, and we cool them by affixing a heat sink to one side. Sometimes we just blow air over them with a fan. Some…
Paul Uszak
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30
votes
4 answers
Why is daisy-chaining surge protectors not recommended?
I know MOVs inside surge protectors degrade over time, but I also see manufacturers putting notes on the box that the protection warranty is void if I daisy-chain surge protectors.
So questions:
Is there an estimate of what the life of a MOV is…
sekharan
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30
votes
4 answers
What software was used for drawing this schematic?
I was reading a book on digital electronics and the gates with more than two input are drawn differently. I have seen many books that draw schematic in this style. I was wondering what software did they use. I am specifically talking about the way…
sigsegv
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30
votes
9 answers
Why execute code from RAM?
I've just come across some macros for my microcontroller compiler to force (or suggest) a function be executed from…
tarabyte
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30
votes
4 answers
Why do smaller loads require larger inductors in buck regulators?
The MC34063 Application Note lists the equation for calculating minimum inductor size as follows:
$$L_{min} = \frac{V_{in} - V_{sat} - V_{out}}{I_{pk}(switch)} t_{on}$$
But this implies that as Ipk(switch) (eg, the maximum switch current) decreases,…
Nick Johnson
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30
votes
8 answers
Why is the diode forward voltage constant?
When you have a diode with a certain barrier voltage (e.g., 0.7 V for Si) and you apply a voltage higher than this barrier potential, why does the voltage across the diode remain at 0.7V?
I understand that the output voltage across the diode will…
sdpatel
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30
votes
6 answers
Parallel MOSFETs
When I went to school we had some basic circuit design and stuff like that. I learned that this was a bad idea:
simulate this circuit – Schematic created using CircuitLab
Since the current will almost certainly not flow equally over these three…
BufferOverflow
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30
votes
7 answers
Why is root mean square used when calculating average power, and not simply the average of voltage/current?
$$P = I_{\text{eff}}^2 \times R$$ where \$I_{\text{eff}}\$ is the effective current. For power to be average \$I\$ must be average current, so I am surmising that the effective current is the average current.
In that case, why is \$I_{\text{eff}}\$…
JobHunter69
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30
votes
1 answer
Why charging Li-Ion batteries in cold temperatures would harm them?
Accordingly to what I've found in several sources (user's manual of electronic devices, various forums, e.t.c.) I shouldn't charge my Li-Ion batteries in cold temperatures because this would harm them. However it's completely unclear which kind of…
vdudouyt
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30
votes
6 answers
Does LED brightness change with voltage?
When I was young and learning about electricity, a fabulous tool for understanding voltage/current/resistance was an incandescent lightbulb (in my case it was a small 3V bulb). When you doubled the voltage by putting two batteries in series, it…
Vilx-
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