47 votes

Is this an AC or DC signal?

DC + AC = DC Plainly put: No. It's AC with a DC offset, if you will. This is less about whether the sign changes (that sign is just relative to some arbitrarily defined reference), but about whether ...
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  • 1,731
38 votes

Why do we use polarized capacitors?

The physical size of a capacitor is a function of the thickness of the dielectric (among other things). Early on, it was discovered that the oxides of certain metals (aluminum and tantalum in ...
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  • 164k
37 votes
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How does USB Type C handle reverse polarity / signal duplication

Below is the pinout for the receptacle: ...
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  • 1,023
30 votes
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Does MOSFET let current flow through source to drain as it allows it from drain to source?

Yes it does conduct in either direction. Due to the body diode, most discrete MOSFETs cannot block in the reverse direction, but the channel will conduct in either direction when the gate is biased "...
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25 votes
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How to memorize a diode's polarity in symbol? (self-answered)

Two mnemonic technique I'll mention. Both technique I've learnt from someone else, many-years ago. We can easily remember, anode is abbreviated as A, and Cathode as K. That is standard, and easy to ...
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25 votes

Is this an AC or DC signal?

It has both AC and DC components. Which of these you regard as "the signal" depends on its intent (i.e. on the information content). If it is say analogue audio with some DC in there for ...
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  • 1,415
24 votes
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What does the radiation from an antenna look like?

This image: Is just a drawing, it has no meaning. It does not represent the radiation pattern of an antenna in any way ! Basically all antennas radiate (and receive) the EM waves in all directions. ...
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19 votes
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Why do we use polarized capacitors?

Can I use a non-polarized capacitor with the same voltage and capacitance instead of these polarizing capacitors? Electrically speaking, non-polarized capacitor is always better than a polarized one. ...
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  • 1,685
17 votes
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Packaging polarity indication of a supercapacitor (polarity indicated by arrows)

Since the product you purchased has no background information, you can't be certain. However, the convention for these stacked-disk type capacitors is polarity mark points to negative lead. This is ...
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  • 2,788
16 votes

How to check DC polarity using a multimeter

I just measured a Lithium battery with unknown polarity with a digital multimeter and got the following measurement. The same results should apply for other DC sources: I hypothesized that the ...
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  • 16.9k
16 votes
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Can current flow both ways through a transistor?

A NPN transistor basically is a stack of three differently doped areas of a semiconductor. The first is N-doped, the middle P-doped and the last N-doped. So yes, on the first sight, you can swap ...
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  • 8,440
13 votes
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Are Peltier elements polarized?

A TEC is polarized in the sense that how it is connected matters. If you want to be able to heat and cool an element then a full Hbridge will work. This will allow you to pump current both directions ...
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  • 2,328
13 votes

Is this an AC or DC signal?

The signal is changing direction with time (alternating), as well as continuously changing amplitude with time. I would call that an AC signal of 18 Vpp with a DC offset of +1 V.
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  • 10.3k
12 votes

How do I decide what capacitor to use in a circuit?

In the case of the 7805, which is unconditionally stable, the type and value of the capacitors is not very important- as the note says, you can leave them out entirely and it will 'work' and will not ...
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12 votes

Reverse polarity protection idea

This question has gone from a 'simple project query' to a good example in both question asking and design, by the addition of key information buried in added comments. The added-in-comments advice ...
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  • 142k
12 votes

Is this an AC or DC signal?

This is really a terminology question. For instance, Wikipedia has a classification under which your signal would be called either "Alternating" or "Pulsating": Clarify with your ...
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11 votes
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What is the polarity of this barrel plug with a double circle?

The outer cylinder is negative with the inner surface being positive. The tip connects to a Maxim One-Wire memory in the power supply that is read by the computer to obtain information such as power ...
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  • 29.1k
11 votes

Why is this 3-way speaker wired this way?

and 2. As I recall from some professional audio gear manual (made in 1980s) that I had to mess with, miswiring +/- at the speakers is the common reason for big "trenches" in the spectrum ...
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  • 5,413
9 votes
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Confusion about dot convention in an ideal transformer

Note that in case (a) the ratio of the currents is negative while in (b) it is positive but the secondary current arrows are reversed. They both, effectively, say the same thing. I've never seen it ...
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9 votes

What does the radiation from an antenna look like?

It really depends on the kind of antenna. Google will probably answer this with pictures better than I will (Google "antenna radiation pattern"). You will distinguish in shape of radiation mainly 2 ...
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  • 221
9 votes
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astable multivibrator: capacitor polarization

Good question. First off, the polarity of the capacitors in your picture is the wrong way around. The + terminal should not be connected to the base of the transistors. Why the circuit works (when ...
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9 votes

Why does this two terminal inductor have a polarity?

Murata has a site specifically about that "polarization" mark. It isn't so much polarization as that the chip its self is in some way asymmetrical so that it changes its electrical properties ...
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8 votes

SMD LED polarity marking: is the cathode marking standardized?

It is entirely per component manufacturer, and when the PCB is manufactured some companies will ask that component placement overlays are given with designators are provided and polarity marks for all ...
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  • 6,198
8 votes
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Do electret microphones have polarity?

Yes, they have polarity and it has to be right to work- the output needs to be biased positive with respect to the ground terminal. The ground/GND terminal should be common with the case, so you can ...
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8 votes
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Fundamental questions about BJT transistors

First let's clear up some of your misunderstandings. This will take some time. Doping does not change the net charge. For every phosphorus atom introduced, a free electron is introduced. But also, an ...
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  • 1,875
8 votes
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Troubleshooting why Powerbank Doesn't Charge Cell Phone

A device (phone) gets charged at optimal (high) rate only when it recognizes "charging port signature" on charger side. For Type-A port, there are several DIFFERENT port signatures that a charger port ...
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  • 37.3k
8 votes

Determining the correct polarity of a supposedly wrong polarized capacitor

That's funny, they actually added two plusses to the screen and they still put it in backwards. You could power it up and see which pin is more positive, but powering it up without the cap may also ...
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8 votes
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Why is the electrolytic capacitor not polarity sensitive?

An aluminum electrolytic will handle a reverse polarity of about 1 volt or so. The cap probably never sees anything near that. This appnote from Nichicon shows that under 1V the capacitors don't ...
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  • 2,177
8 votes

Why do we use polarized capacitors?

Since you mention protection I'll add that polarized caps should not be used for reverse polarity protection. They will react on a reverse voltage very slowly (seconds or minutes), while typical ...
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7 votes

DC Motor as DC Generator + Output Polarity Switcher

You can use a simple bridge rectifier to get what you want. This requires that you must rotate the motors with a minimum speed so that the diodes are forward biased and the output is available.
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