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Questions tagged [dc]

DC stands for Direct Current, which means the flow of electric charge in a single direction. Examples of a DC source are batteries, solar panels, dynamos.

60
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9answers
223k views

How does a capacitor block DC?

I am confused with this! How does a capacitor block DC? I have seen many circuits using capacitors powered by a DC supply. So, if capacitor blocks DC, why should it be used in such circuits? Also, ...
13
votes
14answers
23k views

Why are the power transmission/distribution systems AC and not DC?

Is there a good reason why we are not in the process of completely converting our electrical transmission system to DC? The main reason for using AC on the grid (no offense Tesla, I love you man) was ...
15
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6answers
3k views

RF Energy Harvesting

Why can energy invested in RF radiation not be harvested fully? What are the main factors that affect this? Is there any significant research nowadays that fully describes this process? I stand on the ...
43
votes
7answers
172k views

230V AC to 5V DC converter, lossless

Is there any IC which converts 230V AC to 5V DC? As lossless as possible. I want to connect my microcontroller to an ordinary electrical socket and I don't have enough space available. Thanks.
39
votes
3answers
51k views

Switching DC with MOSFET: p-Channel or n-Channel; Low Side Load or High Side Load?

I think, it is time I understand working principle of MOSFET transistors... Suppose that; I want to switch voltage on a resistive load by a MOSFET transistor. Any control signal between -500V and +...
17
votes
6answers
9k views

What are the highest DC and AC voltages or currents that can be considered as safe?

By safe I mean safe for us when we touch a wire that is not insulated. I have heard that human body resistance is normally 50k Ohm when dry and 20K Ohm when wet. Therefore, these voltages or currents ...
36
votes
11answers
139k views

What would happen if I connect two different DC voltage sources in parallel?

I have a computer power supply that I'm hacking together as a bench supply. For this particular model to power on, I need a minimum load across both +5V and +12V. "Easy," I thought, "I'll just ...
1
vote
1answer
476 views

Draw power from a portable mobile charger to power circuits

I usually power my beginner prototype circuits using mb102 power supply board, but it needs an external elimeter to draw power and then regulate it. I was looking for a portable solution for my 5 ...
17
votes
3answers
26k views

DC biasing audio signal

I have seen a few different ways of adding DC bias to an audio signal. I have simulated them and they all give me similar results, but I cant Figure out is why choose A over B or C. My audio source ...
17
votes
6answers
55k views

Why is feedback required in op-amp circuits?

I understand that, in order for an op-amp to function correctly, a DC feedback loop from the output to either the inverting or the non-inverting input (depending on the external circuitry) is required....
24
votes
1answer
19k views

What to do with third contact in DC barrel plug with only two input contacts

My AC-DC adapter gives output of 12V and GND. I tried to search for suitable DC barrel plugshttp://media.digikey.com/photos/CUI%20Photos/MFG_PJ-037B_tmb.jpg and found that most of them have three ...
1
vote
3answers
615 views

DC operation for IRFZ44 mosfet, SOA curve, max current at 40V?

I have built an electronic load. At the time I did not understand the SOA curves. Now I find the IRFZ44 datasheet does not have the DC curve. Any idea what the max current might be at 30V and 40V so ...
17
votes
4answers
11k views

Cellphone charger has no transformer?

I opened up a really tiny mobile phone charger I have, to see how it is designed. The entire "charger" is integrated into a small 2-pin mains plug, 1 x 1.25 x 0.5 inch, that has an USB socket for the ...
13
votes
3answers
40k views

Scale 30-50 mV signal to 0-5 V range

I have a CO2 sensor that output signal values 30-50 mV. I need to translate these voltages to 0-5 V for my microcontroller with the highest resolution. I understand that I can amplify the ...
12
votes
4answers
132k views

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. ...
6
votes
5answers
46k views

What are the differences between an AC and DC coil relay?

If a DC coil was just a coil, it would saturate. If an AC coil was just a coil, the magnetic field would drop to zero at 120 Hz and the relay would chatter. Presumably the designs in some way prevent ...
2
votes
2answers
4k views

Low Voltage AC Smoothing Capacitor Calculation

I have a 9V AC source which will have a max load of 100mA. I'm trying to figure the value of a smoothing capacitor with less than a 10% ripple. I don't have a scope or else I'd just try a bunch out. ...
22
votes
2answers
25k views

How do the tiny AC->USB power supplies work?

The iPhone and Kindle both come with tiny power supplies that take in 120v AC and output around 5V at 0.85 to 1 amp. They seem to be too small and light to have a transformer, and generate very little ...
16
votes
3answers
44k views

Why is PWM used to control DC motor speed instead of using a variable resistance?

My question is at the end (to change the speed) we are controlling the input voltage of a DC motor in both PWM (pulse width modulation) and variable resistance cases. Is the only reason for choosing ...
5
votes
5answers
31k views

Why do electronic circuits need their power supply to be DC, or rectified AC?

I'm pretty sure the answer to this should be obvious - even to me ... It's been a while I've been reading and attempting to construct simple electronic circuits. The supply almost always is either ...
3
votes
3answers
2k views

Dangerous AC or DC [closed]

Is alternating current more dangerous than direct current? And give me explanation for that... Assume that 230 V, 50 Hz AC voltage and 230 V DC voltage. Which is more hazardous to ...
3
votes
1answer
14k views

DC Motor as a Generator Voltage and Current

Is there any way to calculate the expected voltage and current, assuming I am turning it at the specified RPM value, when using a DC motor as a generator without physically testing it? In my case I ...
2
votes
3answers
277 views

Single supply op amp to convert 0-5VDC to +/-2VDC (microcontroller to line level)

I am generating a 0-5 volt sine wave using an arduino with a DAC. I would like to level shift this signal (DC bias?) by -2.5 volts and have a gain of .8, so that I end up with a line level sine wave. ...
0
votes
1answer
2k views

Controlling a single phase AC fan with a 0-10V DC input

I have a fan motor which is a permanent split phase single phase capacitor motor: http://uk.rs-online.com/web/p/axial-fans/2781543/ I currently control this fan's speed with the following controller:...
5
votes
1answer
6k views

How to couple a signal on to a DC line

I am using DPSK modulation on my signal and want to couple this onto a DC-signal. How will the hardware be set up for this? Is it enough to just couple my signal through a capacitor on to the DC-line? ...
1
vote
2answers
2k views

How to add ground to DC circuit?

I'm just a dabbler in electronic circuits and I'm really still kind of a noob. I am working on a project called the "Atari Punk Console" (Originally known as the "Stepped Tone Generator") but there ...
0
votes
3answers
6k views

Switch current rating AC vs DC

I'm looking for a high current DC switch (able to switch something like 5V@30A) and I've encountered several DPDT that might do what I need, however they are only rated for AC applications (3A@250VAC ...
25
votes
9answers
10k views

How do I power/wire something that is rotating constantly WITHOUT extra batteries?

So I want to make a Lazy Susan that is rotating constantly in one direction. I also want to have some other things on top such as neon signs, moving things, and etc. Problem is I want this to all run ...
15
votes
3answers
55k views

Wiring a DC socket - why three pins?

I have this DC socket: Which I intend to wire up to a circuit to provide power. I have a DC power supply which has a positive tip polarity. I'm good to go and wire up the socket but I am a little ...
19
votes
6answers
15k views

Why are DC signals bad for loud speakers?

I googled and found out through some forum that: DC has a constant amplitude which overheats and destroys the voice coil of the speaker. Could someone clarify if this answer is complete and ...
9
votes
2answers
10k views

Methods of filtering noise caused by DC brush motors

I am looking for any information that would help me reduce the power rail noise and EMI of DC brush motors. I am building a robot that is powered by 2 x 250 W 24V DC motors. Thank you in advance
4
votes
1answer
4k views

Why does capacitor value changes when capacitor is DC biased?

I have seen ceramic capacitor value varying under various DC biased levels. Dc biased was a huge factor as capacitor value is reduced by 50% almost? Why?
4
votes
2answers
877 views

Are we close to a pure DC (or hybrid) household? [closed]

This is a philosophical question. Over the last few years, many of the household devices, particularly those that are more mobile and etc are DC devices. Are we at some point where a DC household may ...
3
votes
2answers
2k views

Why do switches have a current and voltage limit?

I want to attach a switch to a 5 Volt battery pack to be able to turn it on and off. The batteries will power 4 DC motors. The current draw will be about 1 Amp. The switch I have is like the one here. ...
6
votes
1answer
2k views

Grounded AC-DC power supply, what connects to earth ground?

In an AC-DC power supply, how is earth ground typically used? Take a common PC power supply as an example, does the earth ground connect to the metal chassis? Does it connect to the DC ground on the ...
6
votes
4answers
2k views

Short circuit = zero voltage?

Reading this question and its answers (as well as other questions), it seems that in an idealized short-circuit with zero resistance, one concludes the voltage is zero. This seems completely wrong. ...
3
votes
3answers
18k views

why do rectified voltage boosts after adding a capacitor?

So I found this 9V 1A AC power supply laying around and decided to make a DC source. I rectified and added a capacitor to make things a bit even. After adding a capacitor my voltage boosted from 9V ...
2
votes
3answers
1k views

What is the advantage of a switching over a linear power supply?

I want to build my own switching power supply. I already know how to make a 10 Ampere Linear supply, and I'm wondering if I should bother. What do I have to learn to do a switching supply? What makes ...
2
votes
1answer
441 views

A question on PWM frequency of a DC motor

I'm planning to pwm-control four of the following motors by a single ArduinoUno: http://uk.rs-online.com/web/p/axial-fans/8179151/ For some reason the nearest pwm frequency I can set is 31kHz. The ...
2
votes
1answer
3k views

Amplifying signal from CO2 Sensor

I am trying to amplify a MG811 CO2 sensor to a range readable by an ATMEGA2560 (0-5v). I have other analog sensors, so do not want to change ref voltage on Atmega. I have found a module that scales ...
2
votes
3answers
10k views

Why is there alternating current in my wall socket?

Why is the standard of delivering electricity to our homes is via alternating current, and not direct? As far as I know almost every electronic device has an AC»DC converter because their internals ...
1
vote
1answer
88 views

How can I build BJT amplifier with Vin and Vout requirements (peak to peak values)

I have been working on a project but I'm not sure if I'm complying with the requirements that I was given. Design a BJT amplifier such that VIN=0.1 V and VOUT=5 V (peak to peak values). ...
1
vote
1answer
5k views

Arduino SSR 5V DC (Mager GJ-3FA-L)

I just noticed this SSR that was for DCV instead of all the others that are normally for AC. Although I can not find the datasheet for it, it does seem compatible with Arduino. eBay auction site and ...
1
vote
3answers
348 views

Understanding this AC coupled circuit

I'm having a little trouble understanding this circuit and could use some help. So far I understand that this is an AC coupled circuit, and the capacitor is a blocking capacitor. I also know that ...
0
votes
1answer
124 views

What is the correct shunt size for the following ammeter and configuration?

I have the following ammeter: https://www.aliexpress.com/item/Red-led-Display-Color-0-56-Digital-Ammeter-DC-0-100A-4-wires-3-digit-car/1301822575.html The seller recommends 75mV 100A shunt be placed ...
0
votes
2answers
39k views

Why are home appliances and other devices made to operate on dc? [closed]

Why are home appliances not designed to work on ac?why cant we just stepdown the incoming 230V and design the systems to operate at low ac voltages,instead of converting ac to dc?
0
votes
2answers
550 views

Calculating voltage in a simple circuit

If I had a 12V battery and wanted to use an LED that used 2V and 20mA, then I need a resistor that will drop 10V and provide enough resistance to produce a current of 20mA. Therefore I would use R=V/I ...
0
votes
2answers
3k views

What wattage solar panel required for AC 1000 watts

If my house load is 1000 Watts AC/220V, then 1000 Watts DC/12V solar panels is not enough. What wattage solar panel would be required for AC 1000 watts?
0
votes
1answer
3k views

Transformerless power Supply - 24VDC, 120V AC and 230V AC

I want to know if it is possible to design a power supply for a circuit that can operate from DC and AC using the same input terminals. Thus, the output should be xxV DC (5-24 or whatever is decided ...
0
votes
1answer
1k views

dc offset in a miller integrator

I simulated a miller integrator circuit on multisim online. When I did so I made sure that dc offset in the op amp and the source is zero and also bias and offset currents are zero. But in output to a ...