----- Original Message -----
From: "David J Binnington" <david@DJBELECT.KEME.CO.UK>

Hi David and all,

Yes David this is a Strobe light (used for photographic measurements)

> Make sure that you use one complete cycle as the minimum charge burst,
> particularly if you intend using polarized capacitors in the multiplier
> rather than AC rated capacitors or back to back elcos with diodes.  If
> possible use highish value discharge resistors across all capacitors for
> safety.

Yeap, I always put 470K 1W resistors across all my caps for safety discharge
(as I have a split rail on this design I have a pair)

> You could use an analogue comparator circuit to control the charge but as
> this is the PIClist you could use a PIC.  The design of the control
software
> should not be too difficult. Use an A-D converter to monitor the output
> voltage via a suitable divider (use a buffer amp if necessary).  To ensure
> that you can get full cycle control wait until the zero crossing points to
> drive the opto on or off as required. Once the require voltage has been
> reached the triac should switch off and will then keep the output
capacitors
> topped up with brief bursts of one or more cycles.   If the application is
> for Zenon tubes then don't forget to inhibit charging for a short time
after
> triggering otherwise your tube will be fed directly by the charge circuit
> and continue to glow (for a while anyway until something gives).

Ok I am not using a PIC (the client specified an AVR) but I am using a
Microchip A2D that uses SPI ;o)

I have to opto Isolate the A2D as it is very expensive to provide opto
Isolated DC to DC supplies to run the external SPI port for programming and
control and the external RS232 / RS 485 :o(

Ok now my problem, using one full cycle and doing 1 cycle on 9 cycles off, I
get 620Vdc and it does not move :o( I have checked my SCR firing pulses, and
yes they happen every 200ms (I am in Au and we use 50Hz 240Vac (nominal))


So it looks like I have 2 options

#1 heavy loading of the storage caps (atm I have a ~64ma loading from the
opto isolated SPI)

#2 move to phase control and ignore the electrical noise ;o)

Will need to find out what the customer wants to do, as these units are used
in the middle of nowhere (up in mining country in the top of AU ;o)

Regards,

Kat.


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