Re: phase locked loop SSTC

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jan Florian Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>

Hi,

> How is the PLL coming along?  Did you make any sense of my
> last post? 
> http://www.pupman-dot-com/listarchives/2002/January/msg00372.html

Certainly, and your annotations did help to get the picture. :o)

I tried some things, but it seemed all to be rather troublesome, if not
impossible to get working reliably over a freq range of 50kHz-300kHz (or
similar), without much manual adjustments in lotsa places.

So I gave up the "simple" PLL circuit idea and settled for a slightly more
luxurious one. It still uses PLL ICs, but a bit differently.

The "simple" design uses an Atmel 89C52 microcontroller (flash
programmable 8KB rom, 256B ram). 

Just one word, http://www.batronix-dot-com! Super versatile&free programmer
boards, and hobbyist-priced versatile development studio software. (no I'm
not an employee of theirs...)

89C52 uC has three 16b timers. One can be set to output a 50% duty
squarewave. Frequency is programmeable with a 16bit register value,
0Hz..4MHz for a 12MHz clock xtal.  Quite neat, really! It's just
perfect for a SSTC drive signal. :o)

The second timer is used for interruptor mode, i.e. it gives the shutdown
signal to the mosfet gate drives.

The third timer could be used as a frequency counter of some sorts. Or
whatever else comes to mind.

Where PLL comes in is that there are two PLL ICs with identical timing
components (freq range maybe 10kHz to 400kHz). One locks to the uC's
50% duty output signal, the other to the (overdriven) TC base current
signal.
VCO input voltages compared, gives info about whether both freqs are
in-tune or lower or higher. So dynamic tuning should work (although it is
not very fast in adapting, but this can be compensated for in the
software).

Automatic 1/4wave f_res scanning from a small 12V test supply initiated by
89C52. Alterantively manual tuning via up/down buttons or just direct
punch-in of the freq.

The main structures of the real-time OS are already ok. Assembler
code.*sigh*

The two-line LCD panel (salvaged) works fine. Full keyboard input (8bit
parallel => serial) gives some troubles yet. Menu system under
construction. "Run mode" and "user input mode" switching partly finished,
but freq scanning still missing.

I haven't yet hooked it up to any SSTC bridge.

The circuit certainly does require more stuff than a dual 555 timer based
SSTC drive, but, even with the LCD and all, the controller WILL still
fit into the pocket. And isn't very expensive, because components are
standard stuff.

Then it just requires some powerful full- or half-bridge circuit to
connect to. This is probably the more expensive part.

I pray it will work much better than a 555 + manual retuning or
analog feedback setup.
And ok if it doesn't work like desired then it was at least something new
learned (uC programming), with as steep a learning curve as always... ;o)


oops, looks like I wrote 100+ pages of email again... 

bye,
 - Jan

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