Dwayne Reid wrote:
>David Duffy wrote:
>
>>Sounds simple(ish) & obvious!  Hmmm, why didn't I think of it?  :-)
>>I may be able to get away with a power resistor in series with the
>>supply line (between battery & drivers) to limit the current. A lamp
>>would work even better but can't afford an O/C filament to stop the
>>unit from working. The battery supply is 24Vdc and the unit will be
>>for firing fireworks "electric matches" or igniters by remote control.
>
>The fireworks / pyro control systems that my company manufactures does
>things a little differently: the channel 'arm' relay connects one side of
>the igniter to the high side of the battery.  A current sense FET (IRCZ24)
>is turned on when the channel is to be fired.  The current limit is set to
>about 6 amps or so.
>
>Both sides of the ignitor are shunted by the normally closed contacts of
>the arm relay while the channel is not armed.  In addition, both sides of
>the ignitor are floated above ground by a few volts and monitored to look
>for ground shorts or leakage.  Its kind of a bridge circuit - if something
>upsets the balance, that channel is locked out and a fault indication is
>sent back to master control.
>
>Each firing channel uses 3 sections of LM2901 quad comparitor (2 sections
>for the bridge and 1 section for continuity detector), 1 section of LM2904
>dual op-amp (FET driver / current limit), 1 section of NEC EPE series dual
>relay (great little dual 30 Amp SPDT relay), 1 IRCZ24 FET, and about 1/4 of
>a EPM7032SLC-44 epld from altera.  The epld does all the timing and serial
>communications as well as the fault / arm / fire logic required.
>
>In a nutshell, that is how I did our system.
>
>Look over your requirements carefully - there may be no need to use a high
>side driver.  It is dead simple to build a current limited low side driver
>using a sense FET and a single section of op-amp.  As a bonus, the op-amp
>takes care of level translation from your logic supply to the drive
>required for the FET.  The caveat is that you must control what happens
>with the high side supply.  My system monitors for faults before it allows
>the ignitor to be connected to the high side, but this requires an arm
>relay for each channel.  This is a tradeoff that I was happy to accept.

The reason I was going for a high side driver was that this unit is to replace
a manual switch firing unit that uses a common ground system on the
firing rails (right name for them?). Each rail has 20 outputs on it with a D25
connector. I suppose I could use the existing rails but the +/- markings on
each channel would be back to front . (Actually red/black spring terminals)
Getting 100 channels in a small space is going to be difficult & expensive.
Regards...

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