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An antenna feedback question

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Marko

Mon Jun 23 2008, 03:36PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

bluemotion wrote ...

Dr. 2N3055 wrote ...

Ok, so I will just use 74HC14 to get the coil running more reliably. Could it be possible to use just one 74HC14 inverter gate instead of two in series, and reverse the primary phasing? I would like to do this to minimize the delay.

I think it will work. I've done something similar to your concept and it works very well.

How do you intend to start a circuit like this up, in case you are not using filter capacitors and interrupter?

For running halfwave or fullwave rectified input without filtering a separate oscillator is required to kick the circuit in each time the feedback goes away.

Simple NE555 and 100k resistor may be enough for antenna feedback, but not perfect as it will affect stability, and it will not work for CT feedback.

I myself went a step further and used the feedback signal to disable the oscillator and take over the drive through gating logic, and if it is lost oscillator takes back after a small time delay.

This became a quite complex circuit before I was finally happy with it. I can post the schematic if anyone is interested.

It actually isn't any less complex than the best PLL circuit available.

To anyone here, I would personally recommend Steve Ward's PLL circuit. It is the best and most proves SSTC controller available, and can be simplified even further by removing the bilateral switches if interrupter is not used.

Not many know of the circuit and I think it by all means deserves more attention.

Tom540

Mon Jun 23 2008, 05:24PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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I disagree. You don't need an extra oscillator if you're using an interrupter, which it looks like he is. The enabling and disabling of the ucc's causes a glitch which gives some feedback and starts oscillation.
Although my first sstc ran CW and has this same layout except with an antenna and managed to start oscillating as well.

But to be safe if you're going to run it without a interrupter than you could make a start up oscillator using the rest of the hc14 instead of a separate 555 timer.

Steve Ward

Mon Jun 23 2008, 08:24PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

To anyone here, I would personally recommend Steve Ward's PLL circuit. It is the best and most proves SSTC controller available, and can be simplified even further by removing the bilateral switches if interrupter is not used.

Have you tried this one at all Marko? It seemed pretty solid for me (i mean, i did make that beast of a SSTC work very reliably with it), but the bi-lateral switch for interrupting seemed like a bit of a hack, and i never quite liked it so much. The PLL part seemed to work pretty well for me, i could easily target a good phase range, but of course never got true ZCS because the Imag was fairly large in that setup! There did seem to be a slight skewing of the duty cycle always, i was never sure if that was my circuit or maybe the PLL not being perfect. Keeping the DC blocking cap on the primary seemed to eliminate any ill effects of that.

Avi

Mon Jun 23 2008, 10:56PM

Registered Member #580 Joined: Mon Mar 12 2007, 03:17PM
Location: Melbourne, Australia
Posts: 410

just put a 100k (or some other high value) resistor across the inverter gate (Pete says i should call it a NOT gate) (which has the antenna).
This will cause it to self start till the received feedback is of a level high enough to take over.

Marko

Mon Jun 23 2008, 11:19PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I disagree. You don't need an extra oscillator if you're using an interrupter, which it looks like he is.

Well, that is what I said at beginning of the post.

Personally, I don't see much point in interrupter as CW and power arcs are what I like of SSTC. If I was going to use interrupter, the I just go further to DRSSTC.

Have you tried this one at all Marko? It seemed pretty solid for me (i mean, i did make that beast of a SSTC work very reliably with it), but the bi-lateral switch for interrupting seemed like a bit of a hack, and i never quite liked it so much. The PLL part seemed to work pretty well for me, i could easily target a good phase range, but of course never got true ZCS because the Imag was fairly large in that setup! There did seem to be a slight skewing of the duty cycle always, i was never sure if that was my circuit or maybe the PLL not being perfect. Keeping the DC blocking cap on the primary seemed to eliminate any ill effects of that.

Well not yet, primarily due to my lack of understanding of the PLL. I thought the bilateral switch frequency-saving thing is brilliant BTW!

Although it can be completely eliminated if interrupter isn't used.

Contrary to popular belief, SSTC really *never achieves* complete ZCS, because of magnetizing current as you say.

You can *tune out* the phase lag of sinusoidal current which is caused by leakage inductance (Steve, did you find any improvement of the output with that?), but magnetizing current has continuously rising triangular slope and thus it is *always* turned off hard!

Contrary to another popular belief, this lagging magnetizing current is not a problem, or something that should be eliminated, but is *good*, because it introduces ZVS and eliminates diode recovery losses.

Actually, if we removed this magnetizing current and had true ZCS, that would be a death sentence to the MOSFET's. They *need* to switch several amps of magnetizing current to really be happy.
The switching losses occurring during that are actually completely negligible, because mosfets are actually insanely fast, and these would be dwarfed by diode recovery and drain capacitance losses if leading current was driven.

I often see people using additional fast freewheeling diodes in attempt to reduce recovery losses (which doesn't make sense to me anymore since in normal SSTC there's really no forced recovery loss of any kind).

I saw the diodes spinning in and out through times and really never good explanation why should or shouldn't they be there. From my point of view now, they really don't have any purpose.

Marko

bluemotion

Mon Jun 23 2008, 11:32PM

Registered Member #1200 Joined: Mon Dec 31 2007, 01:43PM
Location: Kaohsiung, Taiwan
Posts: 27

Tom540 wrote ...

I disagree. You don't need an extra oscillator if you're using an interrupter, which it looks like he is. The enabling and disabling of the ucc's causes a glitch which gives some feedback and starts oscillation.
Although my first sstc ran CW and has this same layout except with an antenna and managed to start oscillating as well.

But to be safe if you're going to run it without a interrupter than you could make a start up oscillator using the rest of the hc14 instead of a separate 555 timer.

That's right. It works well when running without interrupter.

MRacerxdl

Tue Jun 24 2008, 12:26AM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

I was runned here a SSTC with a Halfbridge of IRFP250 in Fullwave retifier smoothed with 1000uF cap without interrupter, I was using a variac, but I didnt need anything to do the coil starts do ressoate. It was drawing 12A from the 127V Mains (The voltage on the 1000uF cap has 170VDC, much on the limit of the IRFP, but it didnt blow the IRFP250)

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