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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I'd anyway like to know what the resistors and the cap are for. Is it a kind of low-pass filter? Well, then it should work the same if I divide the resistor values by 10 and multiply capacitor value by 10, right?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Yes, it is a low-pass filter and you can scale it like that.
I actually used 100k and 10nF, I don't know why Uzzors changed it to 120k. Maybe he found that it worked better, or maybe he ran out of 100k resistors
PS: You asked when does the circuit change from locked operation to internal oscillator. With a PLL, the question doesn't really make sense. It's always running off its internal oscillator, but when the feedback signal is strong enough, it will start adjusting the frequency of the internal oscillator.
You adjust the pot for maximum spark output, and from then on it should adjust itself to maintain that same spark output.
When using a CT for feedback, there might be issues with the phase being 90' out. I'm sure I remember using a capacitor as a CT burden to compensate it. I was using it to drive an induction heater and the capacitor exploded.
Registered Member #2161
Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247
Late to the party as always.
Steve, I don't know how you managed to get this PLL working, the CD4046, has one of the most worthless datasheets I have come across. Hats off, really.:) It truly is a bullet proof driver once set-up. Also works good with interrupter, just finished that up.
Dr. Kilovolt, I was taking quite a bit of notes when setting the PLL up, and have frequency ranges corresponding to different cap values (with 10k and 15k resistors), I can start looking for the notes it if you are interested. What frequency you plan on running with?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
brtaman wrote ...
Dr. Kilovolt, I was taking quite a bit of notes when setting the PLL up, and have frequency ranges corresponding to different cap values (with 10k and 15k resistors), I can start looking for the notes it if you are interested. What frequency you plan on running with?
That would be great. I think I'll be running around 300kHz.
Steve, I have used both the antenna and CT with the simple feedback 74HC14 SSTC, and both made sparks, so I guess the phase is 0° in both cases.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Dr. Kilovolt wrote ...
brtaman wrote ...
Dr. Kilovolt, I was taking quite a bit of notes when setting the PLL up, and have frequency ranges corresponding to different cap values (with 10k and 15k resistors), I can start looking for the notes it if you are interested. What frequency you plan on running with?
That would be great. I think I'll be running around 300kHz.
Steve, I have used both the antenna and CT with the simple feedback 74HC14 SSTC, and both made sparks, so I guess the phase is 0° in both cases.
For my PLL sstc running 300KHz, i used a 12K on pin 11, and 16K on pin 12, and a 1nf capacitor instead of the 330nf cap on pins 6 and 7. That sounds weird, it sounds like 500pf would be the right value for 300KHz, but nah. 1nf :P. You should try to use a precision pot to control the VCO (the only pot on the circuit). Or, alternatively you can use something like a 10K pot, with a 1K pot in series for better accuracy, without having to turn a pot 15 times with a screwdriver so small you have to make it -.-
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
brtaman wrote ...
These 4046 chips are pretty weird, I get some variation between the chips, but I think the main difference would be from supply voltage?
Uzzors also used a much higher capacitance than me for a freq ~250kHz. Whereas my 220kHz coil runs perfectly for me with the 650nF 10k and 15k.
There ya go, it may be the voltage :P. I used regulated 12 volts, though. Hmmm. Then again, my VCO was set at 300KHz, after the feedback starts, the frequency will change to lock with the feedback, so you may have wondered pretty far from the VCO freq. And then the voltage difference could have made it a few KHz off. I don't know.
Just try the ~500pf capacitor that Brtaman suggested. Good luck :D
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
Steve McConner wrote ...
I actually used 100k and 10nF, I don't know why Uzzors changed it to 120k. Maybe he found that it worked better, or maybe he ran out of 100k resistors
The latter.
The VCO is as the name suggests a voltage controlled oscillator, so supply voltage has a direct influence on it's range. I've never bothered trying to math out the resistor and capacitor values. Just make an estimate and adjust the values through trial and error until you get the range you want.
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PLL SSTC, how to set it up?
