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

Started by in sci.electronics.design8 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 ...

## Ideal vs. lossy transmission line model question

Started by in sci.electronics.design9 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...

## Question regarding diac-triac lamp dimmers

Started by in sci.electronics.design9 years ago 8 replies

Could some electronics guru please hekp ? Maybe this is a stupid question, but here we go. Simple AC kine based lamp dimmers use a diac...

Could some electronics guru please hekp ? Maybe this is a stupid question, but here we go. Simple AC kine based lamp dimmers use a diac triac pair with a capacitor that gets charged via a resistor chain that includes a potentiometer to control the charging rate. When the capacitor gets charged, it discharges via the diac, and this in turn triggers the triac. So far so good. But t...

## Large Noise from Bridge Rectifier; Conducted Emission Measurement

Started by in sci.electronics.design9 years ago 21 replies

Hi I am working on a high power frequency inverter (> 1kW) and have a "funny" looking emission graph The converter is the typical inverter...

Hi I am working on a high power frequency inverter (> 1kW) and have a "funny" looking emission graph The converter is the typical inverter type, EMC filter-> 3 Phase Rectifier-> DC Inductor-> DC Link capacitor-> 6 switch Inverter-> Motor Like this: www.electronicsdesign.dk/tmp/Inverter.jpeg We stripped down the circuits and isolated the noise to the EMC filter and bridge rectifier. T

## single transistor oscillator

Started by in sci.electronics.design10 years ago 11 replies

I tried building a single transistor LED flasher like this...

I tried building a single transistor LED flasher like this : http://cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html I didn't have the recommended 2n2222 - I tried with a BC548, 2n2369 and 2n3055 - None of them work. I'm using a trimpot set to 2 kiloohms and a 470 microfarad capacitor. Instead of a 100 ohm resistor I put 3 superbright LEDs in series. I get 1.2 v...

## Motor starting switch

Started by in sci.electronics.design10 years ago 18 replies

pain in the tail, my FAIP H150 electric power washer died. The motor starting capacitor went (oozed out the side of plastic shell). Replaced it...

pain in the tail, my FAIP H150 electric power washer died. The motor starting capacitor went (oozed out the side of plastic shell). Replaced it with a similarly rated phenolic case starting cap but noticed it's getting very warm. More than likely the motor centrifugal switch is stuck closed. It is a TEFC motor so getting to the switch is a major pain. Not to mention that I don't see a re...

## Phototransistor fed to a transimpedance amplifier

Started by in sci.electronics.design7 years ago 45 replies

Hi all. I'm running through some test of a phototransistor signal conditioner, and I'm facing with wild noise issues. The conditioning is a...

Hi all. I'm running through some test of a phototransistor signal conditioner, and I'm facing with wild noise issues. The conditioning is a basic TIA stage: http://i.imgur.com/PcgglKZ.png Feedback resistor is 5K, feedback capacitor is 470pF, negative bias is -12V, and photocurrent is in the range 8uA-800uA. The bandwidth should be about 50kHz. Opamp is OPA2277UA. Problem is that phototrans...

## Cap Multiplier, NOT a "gimmick"

Started by in sci.electronics.design10 years ago 13 replies

Here's a way to do capacitor multiplication... limited only by OpAmp GBW product, and no resistive components until the OpAmps run out...

Here's a way to do capacitor multiplication... limited only by OpAmp GBW product, and no resistive components until the OpAmps run out of steam. Mathematically, this is the same way I did behavioral models for crummy capacitors such as X7R and Y5U, except I had ideal amplifiers, and equations and/or tables to des

## Crapacitors

Started by in sci.electronics.design10 years ago 75 replies

4.7uF 6.3V X5R dC = -70% @ 6VDC (!!) http://psearch.murata.com/capacitor/product/GRM188R60J475ME19%23.pdf James

4.7uF 6.3V X5R dC = -70% @ 6VDC (!!) http://psearch.murata.com/capacitor/product/GRM188R60J475ME19%23.pdf James

## Dots on inductors

Started by in sci.electronics.design11 years ago 20 replies

I read many years ago (National app note from memory) that one should connect the inner layer of an inductor to the switch in a buck regulator...

I read many years ago (National app note from memory) that one should connect the inner layer of an inductor to the switch in a buck regulator and the outer layer to the capacitor as the outer layer will then act as a screen. I don't know if it makes a difference in practice but it's free. With many modern inductors it is impossible to see how they are wound so the only indication of "po...

## fast ramp follies

Started by in sci.electronics.design6 years ago 139 replies

OK, I need to charge a capacitor with a stable constant current. The desired slope is about a volt per nanosecond. So I did...

OK, I need to charge a capacitor with a stable constant current. The desired slope is about a volt per nanosecond. So I did this: https://dl.dropbox.com/u/53724080/Circuits/Fast_Ramp.JPG Things like this tend to oscillate, so I used a fairly slow, high-beta transistor, BCX71K. The ferrite in the collector is supposed to isolate the ramp cap from the transistor capacitance and make ...

## I think I now know what the SAC722 is and the function of the board.

Started by in sci.electronics.design11 years ago 1 reply

Earlier I asked if any one had some data on a Motorola part "SAC722" and I have not had any response to it, however, I think I now have it...

Earlier I asked if any one had some data on a Motorola part "SAC722" and I have not had any response to it, however, I think I now have it all under the hood. These units appear to be TRIACs, and there are two of them in series, maybe for redundancy? Any way, there is a REED contact envelope in there with a couple of turns on it that monitors an 1/2 HP AC capacitor start motor. ...

## simple opamp amplifier circuit

Started by in sci.electronics.design11 years ago 23 replies

I'm simulating on LTSpice, a simple amplifier circuit with a 2.5V offset, but if I don't include a capacitor on my input my output hits the...

I'm simulating on LTSpice, a simple amplifier circuit with a 2.5V offset, but if I don't include a capacitor on my input my output hits the rails... why is this? The link shows what I'm doing in LTSpice thanks http://i555.photobucket.com/albums/jj477/panfilero/Capture-1.jpg

## Favourite parts with off-label uses?

Started by in sci.electronics.design3 years ago 142 replies

Following up on blocher's sterling work,(*) Many of us use parts off-label, often very successfully. A few examples: SAV-551+ pHEMTs make...

Following up on blocher's sterling work,(*) Many of us use parts off-label, often very successfully. A few examples: SAV-551+ pHEMTs make very good wideband bootstraps. Their f_max is around 12 GHz, but they're amazingly stable. 74HC4352s make good flying-capacitor diff amp front ends. TMUX1511s make very nice analogue lock-ins--their Coff*Ron FOM is almost in a class with relays, but...

## Breakdown voltage of PETG in Homemade Capacitor

Started by in sci.electronics.design14 years ago 3 replies

I'm working on building a high voltage capacitor. I have heard that PET has a very high voltage breakdown. I came across an excellent source of...

I'm working on building a high voltage capacitor. I have heard that PET has a very high voltage breakdown. I came across an excellent source of PETG (Polyethylene Terphthalate Glycol). How much will this affect the puncture resistance? I did a bench test that went alright for being in open air. I'm confident it will handle the voltage I need, but I'd still like some solid numbers. Couldn't fi...

## AC offline to low-V supply, with a cap

Started by in sci.electronics.design5 years ago 77 replies

Years ago we had threads about the ugly but seemingly simple scheme to get 12V DC at 5mA, etc, with a film capacitor straight to the AC ...

Years ago we had threads about the ugly but seemingly simple scheme to get 12V DC at 5mA, etc, with a film capacitor straight to the AC line. We said, gotta have a series resistor to minimize the startup inrush current. Does anybody recall a specific instance of this scheme being used commercially? Paul and I are days away from turning in the manuscript on our new x-Chapters ...

## SPICE microstrip dipole antenna model

Started by in sci.electronics.design3 years ago 2 replies

I am experimenting with SPICE microstrip dipole antenna models. The series RLC lumped element model is assumed. For a half-wavelength microstrip...

I am experimenting with SPICE microstrip dipole antenna models. The series RLC lumped element model is assumed. For a half-wavelength microstrip dipole antenna, the inductance value of the two microstrip segments is computed using values for trace width, thickness, substrate thickness and effective dielectric constant. The capacitor value is obtained by using resonant frequency

## Some capacitor leakage measurements

Started by in sci.electronics.design3 years ago 34 replies

https://www.eevblog.com/forum/metrology/film-and-ceramic-capacitor-leakage-current/ Tim -- Seven Transistor Labs, LLC Electrical...

https://www.eevblog.com/forum/metrology/film-and-ceramic-capacitor-leakage-current/ Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/

## Can anyone explain how this battery charger works?

Started by in sci.electronics.design2 years ago 130 replies

https://imgur.com/a/b8l5qKQ Look at the circuit diagram. The positive of the battery is only connected through a capacitor. How can a...

https://imgur.com/a/b8l5qKQ Look at the circuit diagram. The positive of the battery is only connected through a capacitor. How can a capacitor possibly pass DC current to allow the battery to charge?

## high voltage charge pump

Started by in sci.electronics.design4 years ago 89 replies

Anyone familiar with a high voltage charge pump designed as a step down power supply? The voltage is between 175 & 200. Numerous high...

Anyone familiar with a high voltage charge pump designed as a step down power supply? The voltage is between 175 & 200. Numerous high voltage versions exist using inductors, (Onsemi has one that is "self supplied" which is attractive) but not a one that works with just a capacitor. Are there any out there I've missed? Hul