Questions tagged [formula-derivation]

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398 views

Current gain in MOSFET CS Source degeneration

There is always some formulas for calculating "Au" or "Gu". But there are never given any equations that reffer to current gain in MOSFETs. I know current gain is almost infinite in normal CS ...
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1answer
9k views

I/O Resistance of common source MOSFET with source degeneration

Common Source MOSFET with source degenerations looks like this I am a bit confused about different input and output resistance statements (provided by different sources). Some of them say that ...
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1answer
1k views

Overall and partial MOSFET voltage gain

I am researching studies for common source MOSFET amplifier and I found two different terms for voltage gain - overall and partial. What is the difference between overall and partial gain when ...
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0answers
627 views

JFET transconductance vs. MOSFET transconductance

JFET's n-channel highest transconductance (from datasheets) is marked as In theory, the same value is defined as that applies for n-channel JFET. I haven't found equation which defines MOSFET's ...
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1answer
4k views

Real output resistance of MOSFET

This question is related to MOSFET. NMOSFET's resistance was till now defined in many different ways, for example as: or which value varies from 1-50k Ohm. And there is also drain-source on-state ...
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2answers
2k views

MOSFET finite output resistance in saturation mode

Since MOSFET has finite output resistance in saturation/active mode, the slope of unsignificanlty rising drain current is defined by Ua and slope parameter as lambda: This parameter (as I know) is ...
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1answer
126 views

Unknown Ψ variable in JFET's drain current equation

This question considers unipolar transistor, that is JFET. I really didn't find any other formula than this one which applies only for linear/ohmic/triode region of JFET U/I characteristic. What is ...
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1answer
256 views

Unipolar transistor's transconductance/admittance

Unipolar transistor basic variable transconductance is commonly marked by: It is commonly used in calculations where we need drain current, Ugs, rds(on), and similar. I have also seen many equations ...
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1answer
130 views

Inductance of Shielded Helical Resonators

I found an equation in a thesis which calculates the inductance for a helical coil inside of a cylindrical shield: $$L = (\pi N d_{coil})^{2}\frac{1}{l_{coil} +0.45 d_{coil}}\left(1 -\frac{d_{coil}^{...
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3answers
70 views

Where does the formula for Voltage in AC with inductance come from?

This is what the textbook says: I don't understand why does ωLIm equal Vm so if someone knows please explain it to me Thanks
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5answers
1k views

What is the origin of the capacitance formula?

Everyone knows capacitance is defined as C = Q/V, but why? Sure I understand the utility of it and its use, but can someone provide a motivation or historical context for this definition? I'm unable ...
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4answers
9k views

How to Derive Capacitive- and Inductive Reactance Formula

I've been searching around the internet to find out how to derive the reactance formula for capacitors and inductors. But I couldn't really find anything, so I thought why not make a post about it. ...
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2answers
102 views

Calculating for current in a single transistor amplifier(almost common collector?)

I was given this circuit for a practice test during one of my classes, but we were never shown how to actually solve it. It's just been bugging me so I wanted to know how others solved for all the ...
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2answers
24k views

Deriving the formula from 'scratch' for charging a capacitor

So the formula for charging a capacitor is: $$v_c(t) = V_s(1 - exp^{(-t/\tau)})$$ Where \$V_s\$ is the charge voltage and \$v_c(t)\$ the voltage over the capacitor. If I want to derive this formula ...
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1answer
573 views

SMPS Input Circuit - Formulas resolving diodes, capacitors, voltage, etc

For fun, I made a project from an old PSU and the parts inside it, and ended up with my new HVDC power supply. Consider this diagram: Whenever I plug this in to 120 VAC, I measure 350 VDC on the ...
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2answers
469 views

Boost converter component selection

I want to design discrete boost converter with 5 volt input and 24 volt output with load current of 1 amp. How do I choose suitable input and output capacitor and inductor values; what formulas are ...
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0answers
51 views

Problem with complex numbers C||RLC [duplicate]

I would like to bring this formula in the form Re(D) + jIm(D): This is my current progress: My question is: How can I get rid of the imaginary part jωC2*R? When the denominator is completely real ...
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1answer
229 views

math behind complex numbers C||RLC

I have a mathematical problem with the following formula. The goal is to transform this equation to have a seperated real and imaginary part. I have already done this with several other equasions, but ...
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2answers
18k views

When can I use the formula P=V^2/R?

I'm currently learning about the transportation of electrical energy through power lines. I now know that transporting current at a very high voltage cause minimal power loss compared to transporting ...
-1
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2answers
473 views

Derive frequency equations from an active multi feedback bandpass filter

I recently got some help deriving the transfer function of a multi feedback active bandpass filter made from capacitors resistors and an opamp working as an inverting amplifier. The transfer function ...
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4answers
758 views

Amplify 0 to 3.3V input to +/-3.3V

I'm working on modifying a board, while going through its schematic design I came across a section where a DAC output into the range of [0, +3.3V], which is then supposedly gained to +/-3.3V range, ...
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1answer
241 views

How calculate inductor discharge time through LED?

UPDATE Overnight I realized I'd been sleeping as I read part of the textbook I've been using or at least didn't quite fully grasp the purpose of inductor volt-second balance. I added the results of ...
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1answer
3k views

Solar Power Watts/Volts/Amps

I have a 12v battery that is rated at 220ah. I have solar panels rated at 500 watts total. I'm using a MPPT charge controller rated for 12/24 volts I only have a rudimentary understanding of ...
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2answers
451 views

Is voltage divider formula stated wrong everywhere?

Sample voltage divider circuit: simulate this circuit – Schematic created using CircuitLab In this circuit, \$Vout\$ is, by Ohm's Law: $$ Vin * \frac{R2}{R1+R2} $$ But this circuit, by itself ...
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1answer
513 views

How do I calculate, or measure, all values in a simple A.C. circuit?

I'm trying to figure out how all the formulae fit together regarding A.C. currents. Given this circuit and equations: I figured out the following: ...
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1answer
151 views

How can i convert a equation into a working circuit [closed]

How can i convert a Equation into working circuit For Ex : Eb (Back EMF) = V - IR (Copper losses) of a motor. How can i convert the above equation into a working circuit having variable & as well ...
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1answer
704 views

Formulas for Specific Capacitance Measures [closed]

I am designing a charging and discharging capacitor circuit for my power harvester. What I am looking for is the time it charges and discharges respectively. When I lookev over wikia and google. ...
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1answer
482 views

How to interpret the equation \$e=K_e.\omega_m\$ in a BLDC context?

After researching a while on the subject, I noticed that several sources state that the back-emf constant of a BLDC motor satisfies the following equation: $$ e = K_e.\omega_m $$ where: \$e\$ - ...
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2answers
7k views

How to derive the torque expression for a BLDC?

How can I derive the torque equation for a star-connected, brushless DC motor, given its back-emfs waveforms and currents? I'm currently reading the article A Park-like transform for the study and ...
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2answers
3k views

Help in plugging equation in arbritrary current source LTSpice

I cannot plug in the following equation and parameters in arbitrary current source. Any help would very appreciated. ltspice cannot read my parameters..
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1answer
88 views

How do I derive \$(i_x)/(V_A-V_B)\$ in this circuit?

I have this circuit below: http://qph.is.quoracdn.net/main-qimg-a5380479d6b436dcfb9a36252ac3f1c1?convert_to_webp=true Can I make the small signal equivalent circuit as shown below and when doing the ...
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1answer
2k views

Lengthening charging time of a capacitor

Alright, so I got a circuit that charges a capacitor and I want to charge it to a fixed voltage in a longer time than than the current provided would have (as the current provided would have charged ...
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2answers
2k views

Opamp Inverting Amplifier: The case of non-inverting input not being connected to ground

What is the relation between \$V_i\$ and \$V_o\$ when the non-inverting input is supplied with a non-zero voltage level? I have shared my formula derivation below, but I can't validate it since I can'...
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1answer
4k views

How can the Nyquist theorem for the maximum bit-rate of a noiseless channel be derived?

I've been given the formula: $$ I = 2* H * log_2(L)$$ where: \$ I \$ = Maximum data rate in bits per second for a noiseless channel \$H\$ = Bandwidth that the channel will carry (that is, the range ...
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1answer
243 views

Inductance in Transformers inductors

How can I find a transformers inductors value by using the derivative formula? If I want to generate high voltage spikes from a square wave generator of 10V p-p with a source resistance of 50Ω. I want ...
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1answer
733 views

Band pass filter [closed]

What is this bandpass filter transfer function derivation? http://imageshack.com/a/img674/9016/mKXqCQ.jpg
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3answers
5k views

Why is inductance (L) proportional with turns-square (N²)?

We start from the Maxwell's Equation $$ \mathbf{\nabla} \times \mathbf{B} = \mu \mathbf{J} + \overbrace{\mu \epsilon \dfrac{\partial \mathbf{E}}{\partial t}}^0. $$ We take surface integration of ...

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