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131 Threads found on Variable Capacitor
The datasheet shows the oscillator variable capacitor (to tune the frequency) connects to pins 18 and 19. The RF variable capacitor (to peak the sensitivity at a frequency) connects to pins 19 and 20. If you replace the trimmer capacitors then the replacements must have the correct capacitance value. With (...)
Apparently it's a dual variable capacitor, as used in many classical radio receivers. There seem to be four trimmer screws accessible through the PCB. In case of a superhet receiver (presume it is), the matching of both capacitors, respectively the capacitance ratio, is essential for receiver performance. What are you trying to modify?
The AC induction motor may be three phase, capacitor start or a shaded pole type. If you need a precise speed, you need to have a motor with built in feedback. Some of them can be used as position sensor. The current fashion is a vfd- variable frequency drive- it works like a charm on three phase drives. They tend to be more complex. Give more
"voltage < or > ground" can be a DC offset which doesn't change the "effective" capacitance. Or a variable voltage depending on the capacitor voltage (generally a*Vcap). Miller and similar effects are observed only in the second case.
Hi, I need to develop a circuit that oscilates at fixed 100MHz between points A and B Points A and B have atached a variable capacitor from 10pF to 500pF. capacitor variable need to be proportional to DC out at fixed 100MHz between probe A and B. Capacitance meter at 100Mhz to DC out proportional. Check this picture (...)
Hello Everyone! I've a degree in Power Electronics and I'm trying to build a charger with variable output 0-80V and 0-50A aproximatelly. Now I'm stucked with high currents to charge up the large capacitor that I have on the output. I have made and I attach the simple schematics of what I'm having right now. I'm controlling the output volt
124501 Like this circuit Mv1 and Mv2 transistors have their source and drain tied together. What's the purpose. this is VCO circuit, CVar , variable capacitance is measured from which node? X or Y? and that's the output of the VCO?
If this is a free running pulse train (which 1GHz implies) then maybe a capacitor-blocked, DC-restored inverter is your ticket. See this scheme in CMOS RF prescalers (single ended) on PLLs and such. It will burn some excess power but probably no worse than other schemes. Unbalanced or variable duty waveforms, or ones where you need the DC state
Be aware of the self capacitance of the inductor, it can give misleading results. In a RF Q meter, your U is a known current delivered through a very low value resistor (.04 ohms). In series with the earthy end of the L there would be a variable capacitor with a high impedance volt meter across it. So you energise it at a known frequency, and measu
I believe it should be easy to calculate ignition coil current waveforms and required dwell time to reach a specific coil current. Historically, cars had mechanical ignition contacts with fixed dwell angle and thus strongly variable dwell time. Coil current at low engine speed was respectively limited by the coil resistance. At high engine speed
I want to couple a mosfet to a microstrip line and use it as variable capacitor by varying Vgs.But I don't know how to start with the circuit.Can any body guide me?
Hello, i would like to know how i can model a varistor and a variable capacitor depending on voltage. thanks in advance Check the elements on the "Eqn Based-Nonlinear" palette. There you find general equation-based elements and a non-linear capacitor.
A quite simple method: Using a frequency variable sinusoidal generator (with a series resistor such that R>>wL and a decoupling C), and an oscilloscope or an AC voltmeter, measure the resonant frequency of the inductor with a fixed capacitor (frequency that gives maximum voltage in the parallel LC). With current flowing across the inductor (using
It's somewhat funny question, but here it goes. You can find them on HAM radios - it's like a variable capacitor for tuning, but it can be rotated as much as you want. It's used for setting the frequency on digital radios. It just keeps on rotating, doesn't even stop on 360 degrees, you can make as much turns as you want.
hii i write this verilog-a for variable capacitor and i test circuit in hspice but capacitor don't change While i expected capacitance change sinusoidal please help me `include "constants.vams" `include "disciplines.vams" module vccap(Cp, Cn, Vp, Vn); input Vp, Vn; inout Cp, Cn; electrical Cp, Cn, Vp, Vn;
What is the difference if I just use 1 variable capacitor? Your resolution will be a factor of 10 worse (50..55 instead of 0..5 pF).
hi i decide simulate this circuit in hspice but i can't modeling variable capacitor section pleeeease helllp me 117330
Hello, in this multibibrator if the neon bulb is replaced with a variable capacitor and a suitable RF transformer is used, RF damped waves are produced frequency is determined by the resonance of the LC and the d
When you're asking for variable capacitors with 0.01 pF minimal value, did you already estimate the bare pad capacitance? The idea sounds rather unwordly.
The formula is for minimal bootstrap capacitor (an inequality in mathematical terms), so the answer in case of a variable time period should be clear.
IF you can open the probe in a way that allows it to be reconstructed, all you will find inside is a variable capacitor (compensation control) and one or two small resistors. In view of the overvoltage condition, I would replace them all. The parts cost is almost nothing but you might need a degree in neurosurgery to handle the
Ultrasonic transmission requires both TX and RX transducers to resonate at the same frequency. Try adding variable capacitor (10-300 pF) in parallel with one transducer, if no improvement, then to the other. Use a parabolic reflector on one or both sides to increase directivity. Try checking the waveform with an oscilloscope before the amplifier
Hello, Please could you check the attached fan drive circuit for driving the "ebm papst 8218 JH3" fan? Please advise if this circuit is OK? Basically, as you may see, it is driving the fan from a Buck converter. Do you believe that the 10uF capacitor across the fan is enough capacitance? The PWM is at a frequency of 100KHz, and its duty is
Dear all, I need variable capacitor, working at 1-2GHz, with capacitance of 1-5pF. I hope the Q is high enough, such as 200. Can you recommend? Thanks. Yun
It's not strictly MPPT. Rather a variable Vin regulator implementing the function Vin = a + b*Pin
Hi I want to build a variable low frequency generator. Frequency range: 8Hz - 200Hz Duty Cycle: 20% - 30% I could not work out a suitable configuration for a 555 because the duty cycle conflicts when the frequency is increased. Can anybody help me with this issue? Ah yes, 555 is not compulsory.....other devices like op-amp or transisto
I have an incoming variable frequency (1 KHz to 20 KHz) and variable duty cycle pulse. I need to convert the duty cycle into an analog voltage between 0 and 1. I do not have the luxury of RC filtering the pulse using an external capacitor. What is the simplest way to implement this function on chip?
Does anyone know any recent technologies that allow for a variable capacitor with Inductor with high Q . I have seen MEMS - anything else? thanks
Hi all, I want to make a variable DC DC converter using lm2678. The output voltage and maximum current should be adjusted using digital methods (no pots). I have thought of the following circuit. I cannot yet implement it as the inductor will take some time to arrive. Will this work? Do you have any other good designs ? Regards
Hi every body. pls, can any one support me? I need connecting lumped element(variable capacitor) to resonator using cst simulator. warm regards.
In fact capacitive microphones are nothing more than a variable capacitor so needs to be biased. No. Look in Goggle and you will see that the electret mic (that we are talking about) is a condenser mic with a high voltage built into its electret material. It makes a variable low value capacitor with the movin
Do you mean checking how the results change when varying a variable value?
I?m developing a simple, five-frequency superhetrodyne receiver to operate between 2.5 MHz to 20 MHz in which the local oscillator crystals and whip antenna tuning circuits are selected (switched) using diodes. Here?s the problem: The whip tuning circuit is comprised of a single variable capacitor with five fixed-valu
Hello all. Does anybody know how to design the typical VGA for a commercial TV preamplifier? In the picture attached, i dont know if the trimmer (7 to 22 dB) is a variable resistor or a variable capacitor. How does it work? Thank you. 92309
Maybe this can give you some ideas :
I've built a variable voltage DC power supply circuit using an SCR, rectifier and 160v 33uF capacitor. I've got a 7-150v DC voltmeter hooked up to display the voltage. It always reads 160v, even if I use my multimeter. If I remove the capacitor, I get true voltage readings. How big of a load do I need on it to get the correct voltage to (...)
Hello I have a series L/C circuit connected to a vfo. I am trying to figure out different ways to tune it. Right now I am thinking the next ones: 1. L stationary, C mechanically tuned (variable capacitor) 2. L mechanically tuned (inserting or removing cores), C stationary 3. L stationary, C varicap 4. L electrically tune
Hello guys, I'm trying to design reader device for RFID applications. But important thing is that frequency will be variable. For this purposes I can use to options: either for different frequencies use separated output stage with chosen value of capacitor or use one output stage and somehow vary capacitance. What is also important: i use microc
When you say MOS diode are you referring to the diode formed by the drain-bulk PN junction, or something else? Technically MOS diode is a term for a MIS structure which behaves like a variable capacitor, not a diode...
Edaboard says "Invalid Attachment specified." By nature, an impedance matching network with a single variable capacitor can't be adjusted for X and R (respectively phase and magnitude) matching at the same time. A common impedance matching tool is Pi low-pass filter with two varcaps, for a larger matching range, the L should be stepwise (...)
HI i want to have a variable capacitor in ads.this capacitor is a model of a mems microphone.please help me and help me for matching this capacitor with microphone amplifier thanks for your help - - - Updated - - - i want to have a capacitor that variable with voltage and have a flat (...)
Hi, I need to design a variable capacitor SPICE model. I want to do it with look-up table which would contain a C-V characteristic. Can it be done? I simulated a IDC with HFSS and now I want to include the results in Spice model. I never used Spice so I do not know how to do it. Can you help me? Thank you
Hello I am building the attached regen receiver and I replace the variable with a bb212 Double varicap. I connect the varicap like this: It works, but the problem is that when going into oscillation (SSB) frequency fluctuations occur in the oscillating tone (BFO). When using an air variable the t
Define an equation that relates your voltage changing to capacitor value and put this variable in capacitor component as its value. For instance MyCap=0.5*Vtune+10*log(Vtune) etc.Then put this variable into cap value like C=MyCap. It's so straightforward..
hello Why are you using integer for f1,f2,f3,cal1 ? what is the purpose of cal1 and f3 try con1= cx / ((((float)f1/(float)f2)^2)-1); or pass all your variables in floating point format. and you will get 402pF
I have been trying to make a variable capacitor based off of a lookup table in PSPICE. I found a paper by cadence, A Nonlinear capacitor Model for Use in PSpice, which gives a method of creating a variable capacitor but I am unsure how to actually write the .lib file to implement this design. Any (...)
I think it was just to allow flexibility in the wiring layout; in pre-PCB days the wiring was "point-to-point" and a choice of connection point would have been useful since variable capacitors could be mounted in different ways. Both connection points could be used for different components if the chassis layout made that convenient. You don't hav
That "common" connection in the centre is actually connected to the spindle, so in that circuit, when you touch the knob on the spindle you will be adding extra capacity across the bottom capacitor. Just use one section of the variable capacitor, WITH THE CENTRE CONTACT earthed, and wire a fixed 68Pf in series with it. Frank
i am unable to use the variable capacitor in my circuits,i.e, which pin of variable capacitor should be connected to which point in circuit?76193 76194
Hi there, Just joined up to the forums, apologies if this thread is in the wrong spot. I am currently looking at designing and making a piece of test equipment to test the opening and closing time as well as minimum operating voltages of high voltage circuit breakers. The control circuit side of things is no problems but I am struggling to