## "silly" RCL noise question

Started by in sci.electronics.design7 years ago 7 replies

So say you have an RCL circuit and are looking at the Johnson noise (Created by the R) that is across the capacitor. And assume that the...

So say you have an RCL circuit and are looking at the Johnson noise (Created by the R) that is across the capacitor. And assume that the circuit has a decent Q. Then the voltage noise at (and near) the resonance frequency will be Q times higher than it would be without the L and C. This implies (by energy conservation if nothing else) that the voltage noise at frequencies not near t...

## Ideal vs. lossy transmission line model question

Started by in sci.electronics.design7 years ago 25 replies

Could some electronics guru please clarify a few subtle questions regarding lumped parameter model of transmission lines ? The simple...

Could some electronics guru please clarify a few subtle questions regarding lumped parameter model of transmission lines ? The simple loss-less lumped parameter model consists of an ideal capacitor-inductor pair per unit length. OTOH, the lossy model includes a series resistance with the ideal inductor and an dielectric conductance in parallel with the ideal capacitor. Simil...

## Voltage-variable capacitor doesn't work in LTSpice

Started by in sci.electronics.design7 years ago 92 replies

Gentlemen, Setting up voltage-controlled resistors is easy: R=(V(X)+0.01) or whatever. Works, always did. Doing the same with a capacitor...

Gentlemen, Setting up voltage-controlled resistors is easy: R=(V(X)+0.01) or whatever. Works, always did. Doing the same with a capacitor fails with this error message: Error on line 6 : c1 n002 0 c=(v(x)+0.01) Unable to find definition of model "c" * Unknown parameter "x" WARNING: Less than two connections to node X. This node is used by V4. Fatal Error: Missing capacitance ...

## Obsolete Capacitor?

Started by in sci.electronics.design7 years ago 13 replies

Greetings gentlemen, What kind of end product would a capacitor such as this be found...

Greetings gentlemen, What kind of end product would a capacitor such as this be found in? http://www.ebay.co.uk/itm/Plessey-visconol- capacitor-8mf-600VDC-70c-/321396389935? pt=LH_DefaultDomain_3&hash=item4ad4b7b82f Thanks.

## Micro strip capacitor issues and questions

Started by in sci.electronics.design7 years ago 9 replies

Could some electronics guru please help ? Recently, I came upon some literature related to micro strip inter-digitated capacitors fabricated...

Could some electronics guru please help ? Recently, I came upon some literature related to micro strip inter-digitated capacitors fabricated on single side copper clad FR4. Several questions arose in my mind. 1. Is this an air core capacitor with the fingers acting as the plates of a parallel plate capacitor ? Ib this case, for each capacitor's capacitance would be very low, give...

## NFB Rolloff, capacitorless

Started by in sci.electronics.design7 years ago 6 replies

Suppose I have a very simple little class B amp, just an opamp driving a small output pair for a watt or 2, and nfb resistors. Zero output pair...

Suppose I have a very simple little class B amp, just an opamp driving a small output pair for a watt or 2, and nfb resistors. Zero output pair bias, lots of crossover distortion. Now... I'm thinking I can skip a nfb rolloff capacitor by using the opamp's own internal cap to give the rolloff, eg for a 1MHz gbw opamp, if we run it at gain 20, its gain is down in the gutter above af a

## Linear Mode of IGBT FSOA/hotspots? - feasable?

Started by in sci.electronics.design7 years ago 33 replies

Hi For an application I am looking into using a large IGBT for inrush (charge of DC link capacitor from mains) To reduce BoM costs, I would...

Hi For an application I am looking into using a large IGBT for inrush (charge of DC link capacitor from mains) To reduce BoM costs, I would like to drive it in linear mode, monitoring the current and adjusting the gate voltage accordingly There are however some talk about hotspots of a linear mode driven IGBT. The IGBT is a 20A device. My intention is to drive it at 10mA, so 2000 times...

## Shunt resistance to drop capacitor Q

Started by in sci.electronics.design7 years ago 6 replies

What parallel resistance is needed across a 100pF capacitor to drop Q factor to 3 at 1Mhz? (Assuming the unloaded capacitor Q is much...

What parallel resistance is needed across a 100pF capacitor to drop Q factor to 3 at 1Mhz? (Assuming the unloaded capacitor Q is much higher). Reason I ask is that I have acquired a Boonton 72 capacitance meter thanks to Phil Hobbs's and John Larkin's recommendations in this group and now want to check calibration. Manual lists a procedure using a High-Q/Low-Q 100pF test standard where ...

## Flecap

Started by in sci.electronics.design7 years ago 4 replies

This is the Maxim integrated variable...

This is the Maxim integrated variable capacitor http://www.maximintegrated.com/en/products/analog/sensors-and-sensor-interface/MAX1474.html I recall seeing some other parts/vendors somewhere, but I can't find them. It doesn't google well. Any leads? -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtec...

## Diode and capacitor on mains input

Started by in sci.electronics.design7 years ago 11 replies

I'm fixing a B & O amplifier, a pleasure due to the clear schematics supplied with it but do not understand one little area. In series with the...

I'm fixing a B & O amplifier, a pleasure due to the clear schematics supplied with it but do not understand one little area. In series with the mains input there is an electrolytic and a pair of back to back diodes all in parallel. What is this for ? Excuse the poor ASCII art. ---| |--- | | ---||--- Jon

Started by in sci.electronics.design6 years ago 30 replies

I need to draw some simple schematics. 5 to 10 components. Long ago I did them with MacDraw. 30 years later I am looking for something as...

I need to draw some simple schematics. 5 to 10 components. Long ago I did them with MacDraw. 30 years later I am looking for something as simple, runs under windows and has a library of common components (resitor, capacitor, transistor, diode, fuse). In short something with not much of learning curve that will do the job. Does not need to do PCB layout, circuit analysis, etc. It does ...

## Using a Pot to Tune a Coil

Started by in sci.electronics.design6 years ago 66 replies

Please excuse the general question, but is there any way to tune a coil using a potentiometer? For example, let's say one end of the coil is...

Please excuse the general question, but is there any way to tune a coil using a potentiometer? For example, let's say one end of the coil is connected to an antenna and the other end to earth. Would a pot and capacitor (fixed value), each placed in parallel with it allow for the resonant frequency to be adjusted to some degree? If so, how would I determine the appropriate value for t...

## Sizing Resistor Wattage for One Short Pulse

Started by in sci.electronics.design6 years ago 70 replies

I am designing an inrush control circuit to prevent a pair of electrolytic bypass capacitors exceeding their rated ripple current when power...

I am designing an inrush control circuit to prevent a pair of electrolytic bypass capacitors exceeding their rated ripple current when power is suddenly applied. When the capacitor is fully charged it will be grounded by a MOSFET. In parallel with the MOSFET there is a current limiting resistor. I do not know what the rise time of the power supply will be. I do know I must protect aga...

## 40 yr old thought experiment

Started by in sci.electronics.design6 years ago 33 replies

A long time ago, I had this idea, but never pursued it at the time (just out of school). Idea was to make a liquid flow meter with no moving...

A long time ago, I had this idea, but never pursued it at the time (just out of school). Idea was to make a liquid flow meter with no moving parts. So it seemed that if one had a parallel plate capacitor with a bias voltage on it built into a pipe, and pumped a polarized molecule fluid between the plates, there should be some current flowing into the capacitor from the E field trying to ...

## Colpitts crystal oscillator in LTSPICE

Started by in sci.electronics.design6 years ago 59 replies

I'm trying to simulate a low frequency Colpitts oscillator in LTSpice using an NPN darlington and a crystal, and I'm having a lot of trouble...

I'm trying to simulate a low frequency Colpitts oscillator in LTSpice using an NPN darlington and a crystal, and I'm having a lot of trouble getting it to start up. Does anyone have a working one of these? I'm just using a capacitor to simulate the crystal, the parameters I am working with are something like: motional capacitance: 5.3ff ESR = 11k ESI ~ 4500 henries EPR = 100 meg E...

## Nice transistor for capacitor multipliers

Started by in sci.electronics.design6 years ago 23 replies

The 2SD2704K: 870 < beta < 2700, V_CEO = 20, V_EBO = 25 (!), pretty low V_CEsat, ~20 cents. It's slow (35 MHz) but looks great for cleaning...

The 2SD2704K: 870 < beta < 2700, V_CEO = 20, V_EBO = 25 (!), pretty low V_CEsat, ~20 cents. It's slow (35 MHz) but looks great for cleaning up power supplies. The high beta lets you use bigger resistors, IOW longer RCs for the same caps. http://tinyurl.com/oajew3r Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-

## Filter cap choice for ultra low ripple

Started by in sci.electronics.design6 years ago 81 replies

Gentlemen, What is currently the best choice of filter capacitor for the PSU section of a high-end signal generator the output of which...

Gentlemen, What is currently the best choice of filter capacitor for the PSU section of a high-end signal generator the output of which (obviously) really needs to be as ripple-free as humanly possible? Just in *GENERAL* terms, please guys; don't want to get bogged down in specifics and calculations at this stage, please! tia, cd

## Parallel R-C circuit impedance

Started by in sci.electronics.design6 years ago 4 replies

It is obvious that with signal frequency increase, impedance of parallel R-C circuit decreases, since impedance of the capacitor decreases with...

It is obvious that with signal frequency increase, impedance of parallel R-C circuit decreases, since impedance of the capacitor decreases with frequency, and capacitor is in parallel with the resistor. Read more: http://www.cirvirlab.com/index.php/electric/parallel-r-c-circuit-impedance.html and calculate http://www.cirvirlab.com/simulation/parallel_r_c_circuit_impedance_calculator.p...

## Wirekess capacitive power coup;ing

Started by in sci.electronics.design6 years ago 7 replies

Could some electronics guru please clarify a few questions regarding capacitive wireless power transfer. An capacitor is a short to AC, so I...

Could some electronics guru please clarify a few questions regarding capacitive wireless power transfer. An capacitor is a short to AC, so I were to consider a very simple test case of wireless power transfer using capacitive coupling, where the plates of the capacitor are on two different physical devices, how is earth/ground established for the two separate physical devices ? Thanks i...