Author Topic: Parasitics  (Read 990 times)

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Parasitics
« on: November 08, 2015, 00:41:32 am »
i i´m constructing a very nice frequency generator and for it i analysed better how goes the parasitic capacitance of the components extensively to try finding a manner to create a very high voltage pulse without expending much energy other than the primary leakage energy and even try to use it and cycle it back...

i came up in this years with many circuits using non dissipative clamps and found that those are the best when we want to limit the core energy to a certain rate of discharge that wont blow up the components...

in the spirit of doing a better job i filled my circuit with tvs above the clamping voltage so there are 3 levels of protection

1 clamp

2 tvs across primary

3 tvs across switch

so basically across the primary its allowed to go only up to 750v from the clamp when it reach the maximum voltage applied...

the 1 tvs limits the primary to 800v and across the swicth another tvs limits the voltage to 1000v.... the switch limit is 1200v...

i found that the D1 the diode that isolate the source can be mounted on an isolated heat sink in the case and this forms the first capacitance parasite to ground lets call this C1..

d2 i will call the diode that is connected with anode to the oposite side of the primary (fllyback diode) and connected also to the drain of the switch(it does not short the primary it has the 1 tvs set in series with it across the primary.... if mounted in a isolated heat sink also on the (ground) case it also  forms a capacitance to ground which is very interesting one... in the sense that if a capacitor is add in parallel to the parasitic capacitance of d2 to ground lets call it C2 and the second set of tvs also in parallel to it than the voltage at the drain will never get over 1000v... and when it closes it wont have to discharge this capacitor thru it directly because d2 blocks it! the first set of tvs also connected to the cathode of d2 may have a resistor R1 in parallel with it so it can absorb part of the power and partly discharge the capacitor C2 into the primary when the pulse is back on...

d3 across the switch prevents the swicth from having a reverse voltage when the primary receives the resonance voltage back in the other direction... it can be mounted on the same heatsink of the igbt without isolation between the components but the heatsink must be insulated forming a third capacitance between the drain point and ground case... 

C2 can be increased but C3 should not... in my point of view... C2 at will at maximum keep charged to 1000v because of the 2 set of tvs in parallel with it... so when pulse is now back on you get 1000 applied thru the 800v tvs and primary mind that there is r1 in parallel with those tvs...

this c2 will also first discharge into c1 but as c1 is a parasitic capacitance shoudl be very small...

another strategy would be to only put a capacitor in parallel with d1 to get it protected of a back pulse and let it sum with the powersupply voltage during pulse applied

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Re: Parasitics
« Reply #1 on: November 08, 2015, 12:27:12 pm »
Another idea is to instead of using R1 in parallel with the tvs set that is across the primary... to use a coil... however a diode d4 should be added in that case also in parallel with the tvs to improve its conduction when forward biased... allowing the coil to have like a short circuit path to discharge... this will keep the energy into the coil during pulse on... and creates a path for c2 to discharge into the primary again without consuming power.
 

it could also be a switch .... in the end you can see there are many many ways of doing it.. but few ways to do it the best possible...

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Re: Parasitics
« Reply #2 on: November 10, 2015, 06:35:31 am »
today i was testing my new oscilloscope and i found that my fluorescent lights are creating a 13khz overtone over the radiated 60hz from line... initially i thought it was an harmonic but getting probe closer to the lights it reveal the clean 13khz or so waveform...

it gaves me a thought non related... meyer says laser energy can help the polarization process...

laser energy is in the terahertz range which are frequencies where the molecules vibrate not rotate

maybe infrared maybe not

laser is coherent  and maybe pulsing it even at very lower frequency it can hit a subharmonic frequency and induce a resonance or vibration onto the molecule... from my point of view laser will apply kind of a force into the molecules...

if the photons travel thru the cavity imagining mirrors in the ends of the cavity... the question is how would the electric field of the laser be distributed since there is already a high polarization from just voltage...(filds does not cross each other shoudnt they rotate?  how many wavelenghts fits into the tube? wont they ne cancel out in certain cases depending on wavelengh? certainly!
what i mean is that laser is a traveling electric field and magnetic field.. both are perpendicular and 180° apart if i recall well...

what i mean is that if the cavity allow for a 100 wavelengh, half will ad half will be in the counter direction of the applied voltage field and its traveling... inside the cavity this photons can be accumulated... i dont know how but we can try to think about it...

my question is if we are some kind of rotating the molecules if we charge the capacitor and rever its polarity isnt it possible that its oscillating at its self rotating frequency ghz range?

now if you are following..

if we apply a subharmonic frequency... of this frequency... and the cavity is made to have a certain frequency range of operation... my best guess is that if we apply the correct subharmonic could be possible to set up an oscillation in that cavity...