# Questions tagged [capacitance]

Capacitance is the ability of a body to store an electrical charge

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### Why are these capacitors treated as if they are in series? Why must the incoming and outgoing current in a battery always be equal?

A circuit with three capacitors and an open end at A: I am a high school student. I am very confused by this example. The circuit is open at end "A" as shown but still there would be some ...
637 views

### Capacitance of a PCB via

In this article, there is a section that models the capacitance of a via. The equation given is: $$C=\frac{(0.55\epsilon_rTD_1)}{D_2-D_1}$$ Where T is the board layer thickness, D1 is the pad width ...
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### Why is the bridge rectifier circuit widely used to make power supplies?

Why is the bridge rectifier circuit widely used to make power supplies? Which is better - a bridge rectifier with capacitor or without capacitor?
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### Measuring capacitance with an oscilloscope and a function generator

I was looking for a method to measure capacitance at high frequencies and found this document from Tektronix. It shows how you can measure capacitance with an oscilloscope and a function generator. I ...
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### Can a LC circuit generate frequencies in the Gigahertz range or higher?

For instance, if you took a bunch of off the shelf capacitors and arranged them in series and a bunch of inductors and arranged them in parallel, could you make the resonant frequency of the LC ...
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### How does line capacitance of overhead naked lines change with rain or snow?

Does line capacitance change with rain or snow? If yes, does it a lot (or is there a study that quantifies the change)? I ask it because I am studying the tuning of a Petersen coil, and I want to know ...
45 views

### How can I graph the bias voltage vs capacitance in ADS?

I am trying to model a bias tee and control the capacitance of the varactor by varying the voltage. How do I plot the voltage vs capacitance/charge in a graph in ADS using AC simulation?
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### What is a subtle way to disrupt or cause interference to a typical laptop touchpad?

I know touchpads operate based on capacitance and using your finger to sort of complete a capacitor and track movements, etc. Is it possible to confuse or disrupt a touchpad using some other material(...
61 views

### Resistance vs capacitance of conductor

Suppose we have a wire which transmits power. Is there a direct relationship between the resitance (or conductance) of the wire/m and the capacitance of the wire/m? Or they are independent of each ...
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### What is the purpose of these different-value capacitors? [duplicate]

I guess I am trying to figure out why we wouldn't just consolidate these into one single 22.11uF capacitor. My initial understanding was that each capacitor was better at filtering certain frequencies,...
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1 vote
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### Why does high frequency decoupling require a small capacitor?

Why can't a large ceramic capacitor with low ESR feed at high frequency? Maybe becase of resonance, since the higher freqeuency resonance can be achieved by lower C and ESL both not only equivalent ...
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### How do capacitive touchscreens really work?

I have a bit of trouble understanding the electrical laws which apply when I touch a capacitive touchscreen with my finger. Apparently, there is an electric current running through electrodes below ...
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3k views

### What does negative capacitance mean?

I see negative capacitance measuring electrolytic capacitor at high frequencies (40kHz). How should I interpret that? The device is LCR Meter Hantek 1832C. I failed to find anything about that in the ...
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### Can I use a 1kV capacitor for a 5V circuit?

In a different question, it was asked if you could use a relatively higher voltage cap in a 5V circuit (35V cap). It seems that's ok, but I want to know if that logic is still applicable towards the ...
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### How are filters able to pass frequencies correctly when multiple signals are present?

I have absolutely no experience in the world of EE but I'm self studying and I have some questions on how filtering works when multiple signals are involved. I understand the graphs of filters showing ...
1 vote
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### Why conductor having charge(let say 1C) have tremendous potential but same conductor used in capacitor have low voltage?

When we talk about electrolytic capacitors or the supercapacitor(EDLC) then we know that, we can store large amount of charges in it. Since in electrolytic capacitors Aluminum plate acts as cathode ...
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### Limit inrush current for USB and large capacitors

I am building an ESP32 custom board (project link and full schematics/layout.) I want to add USB to it for programming only. Power Supply: USB to serial: During normal operation, the board will be ...
197 views

### Operating Region for Transistor in Capacitance Multiplier

I want to understand what is the desired operating region for a transistor in a capacitance multiplier circuit being used to remove power supply ripple. Consider the circuit in the attached image. ...
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### Why is there electrolyte soaked paper in an electrolytic capacitor?

I know that the soaked paper spacer is there to protect oxide layer but how does it protect it and from whom does it protect it? Why does the paper spacer need to be soaked in electrolyte and what ...
864 views

### Can I increase the output capacitance of a DCDC beyond the specified maximum?

The MPM3822C is a synchronous, step-down, power module with an integrated inductor. According to the datasheet, the maximum output capacitance is 100uF: Questions: Why do they specify a maximum? ...
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I am trying to find the input capacitance for the common source amplifier stage below: - I have tried to find $C_{in}$ by simulation. I apply a linearly increasing voltage source $v_{in}(t) = 1 \... • 2,920 0 votes 1 answer 96 views ### Any short formula for PCB trace capacitance when w/h <<1 [closed] I have this formula/equation e(w/d) for capacitance of PCB traces (parallel plate). But as it appears, this equation is valid for the assumption w/d>>1 (much greater). And multiplying 11.3 with ... • 49 0 votes 2 answers 73 views ### CMOS active crystal oscillator load capacitance, to be used for PLL reference I do not have a clear idea of what load capacitance is. I am looking forward to use the ADF4106 PLL with a ~580 MHz VCO to synthesize the frequency. For the reference input to the PLL, I wanted to ... • 49 2 votes 1 answer 119 views ### Transformer's capacitance Our main purpose is create the transfer function of a transformer, and we want that for a resonance frequency higher than 1 MHz for our LLC transformer in an LED project. https://www.omicron-lab.com/... 0 votes 0 answers 27 views ### What value of capacitor should I use with this MP2307 buck regulator? I am designing a buck regulator using the MP2307 synchronous step-down converter chip, but I've encountered a problem. The datasheet offers this example schematic, for a 3.3V output: I understand ... • 1,119 0 votes 3 answers 88 views ### Estimating load capacitance from inrush current I need to estimate the capacitance of a load for choosing a PSU for it, as they state the maximum capacitance. It is a strobe light so I suspect it will have quite a bit of capacitance. I've tried ... 0 votes 1 answer 131 views ### Motor run capacitor tolerance From wikipedia: If a wrong capacitance value is installed, it will cause an uneven magnetic field around the rotor. This causes the rotor to hesitate at the uneven spots, resulting in irregular ... • 125 0 votes 0 answers 54 views ### How to trigger cap touch sensor without touching it? I have a device that has metal spring connected to microcontroller pin that has in-built cap touch sensing . This spring is used to turn the device on and off. I plan to place the device in ... • 11 1 vote 0 answers 39 views ### How to calculate the total capacitance of many connected parallel traces I have a PCB with 60 or so traces in a parallel geometry such that the traces are connected in an alternating pattern as in the picture. My question is, what is the correct way to calculate the total ... • 11 3 votes 2 answers 432 views ### How can the charge of capacitors in parallel + series exceed the total charge? I'm solving this question: From this video We can simplify the circuit to be a single capacitor with capacitance of 50 micro farads. Using Q = CV, we can determine ... • 189 0 votes 1 answer 75 views ### How to combine elecrolytic capacitors into one big bipolar one I want to make capacitor with large capacity which can hold both positive and negative charges. Is it possible to combine elecrolytic capacitors somehow to achieve this? • 485 2 votes 1 answer 80 views ### How much to increase crystal load capacitance based on this inaccuracy? The frequency of my 40MHz crystal is 10.6 ppm high, how much should I increase my load capacitance? I am using 12pF crystal with 15pF load caps. As I understand if caps need to be unbalanced the ... • 491 2 votes 0 answers 54 views ### Booster Circuit Input Capacitance Design I am trying to design a booster circuit. I need to find the inductance, output capacitance and input capacitance. I have successfully calculated the inductance and output capacitance. However, I am ... • 39 0 votes 2 answers 133 views ### Can I use a multimeter to measure the capacitance of my oscilloscope? I'm trying to measure inductive (not RF) reception in a short-range PKE coil antenna, and that requires a tuned circuit and outputs very low voltage. Does it make sense to measure my oscilloscope ... 0 votes 0 answers 45 views ### Why does changing the emitter-collector polarity change the collector-emitter capacitance? Due to some constraints, I had to use HDMI SDA and SCL lines for UART communication in a mainboard. The circuit works fine but, it fails on HDMI certifications where SCL and SDA line capacitance is ... • 1,211 1 vote 1 answer 65 views ### MOSFET gate capacitance near$V_{gs,th}\\$ (miller plateau)?

I have trouble inferring a realistic value of the gate capacitance for when a MOSFET is used near its turn-on voltage, i.e. not as a switch but as a linear regulator. It's important to find a ...
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### Calculate capacitance needed to actuate a solenoid one time

A 1.2W solenoid has to be actuated for 500 msec, using only a (pre-charged) capacitor. The solenoid voltage range is 4.5-6 V. I have to calculate the needed capitance. https://www.engineeringtoolbox....
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### Capacitance value after actuator load

I need a little help with the capacitor (in green) in the image above. The problem seems similar to filtering the output of a rectifier but instead of the voltage oscillating back and forth between 0 ...
1 vote
198 views

### Capacitance between two parallel plates

My teacher told that, Consider a parallel plate capacitor of capacitance C, if we isolate one of the plate, then capacitance of that plate becomes double i.e 2C. Can anyone help me out in finding ...
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### Estimating load capacitance when connecting two opamps?

I plan to use the OPA657 as a charge sensitive pre-amplifier for measuring the output from a reverse biased PIN photodiode. I would like to further amplify the signal using a wideband EL5163 opamp. ...
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### How to model a 10 m twisted pair wire

I would like to model a 10 meter twisted pair wire from a CAT 6 ethernet cable. I'm trying this out so that I can know if my driver circuit is capable of sending a signal that is still acceptable for ...
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### Measure capacitance of planar electrodes for sensing gas using Arduino/Nucleo board

I am looking to do post-grad research study next year in the sensory field for sensing gases like hydrogen, nitrogen or ammonia (not decided yet). So trying to understand what is out there and how ...
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### Input Source Capacitance Value for GBW Calculation

For the calculation of GBW product for a photodiode: Which diode capacitance value do I use for the input source capacitance (Cs)? I am having trouble understanding the difference between the 400pF ...
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### Simple series capacitance circuit

I am a semi-retired Electrical Enginerr, and this question has me perplexed. I don't need any info on capacitors, series calculations, transition effects, etc... Here is the complete question but I'm ...
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### long cable capacitance consideration when the output is tri-stated

I have 50 devices that are sending data to one MCU through multiple 3 meter data cables. The data signal lines merge at the MCU location. Only one device will send data at a time at 5 MHz+ data rate. (...
196 views

### What are the consequences of using a capacitor that is of higher capacitance?

I'm troubleshooting a circuit board that has a dead short somewhere. I removed some capacitors which were shorted in circuit but the problem was elsewhere on the board. When testing these 1500uf 2.5V ...
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### What is the derivation of this formula of potential difference related to the capacitance of a two wire line?

From this lesson: https://circuitglobe.com/capacitance-of-transmission-line.html Basically, I don't get where the formula came from. I am aware of the V = Q / C but I'm not that familiar with ...
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### Calculate capacitance given I and V graphs

There's this question which asked us to find the capacitance value give both (v-t) and (i-t) graphs for capacitor. Here are the graphs: This is how I calculated the capacitance: It was obvious from ...
1 vote
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### Voltage spikes in a power supply

I've been testing a power supply I've made and noticed that a +/- VCC voltage spike occurs when a resistive load is attached/disconnected (or when a power is lost) due to capacitor transients. The ...
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