At 04:23 PM 8/15/00 +1000, David Duffy wrote: >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. Makes perfect sense, then. You have a matrix system and you really don't want to have to go into the firing slats and turn all those steering diodes around. What exactly is your goal? I'm assuming that your existing system fired only one channel at a time? How many channels at a time do you want to fire? How are they being fired? Is it a simple sequencer or do you need random access? Blue Smoke out of Calgary does something similar - they have 16 channels on each of 16 common lines for a total of 256 channels. They can fire any or all of the 16 channels associated with each common line but can't fire channels that span multiple commons in the same instant. Not much of a problem for fireworks shows. Just how many high side drivers do you need? 20? How long is your firing pulse? You might consider doing it the 'brute force' method - TIP32 transistors with small emitter resistors and 2n4403 transistors doing the classic 2 transistor current limit. If you limit your fire pulse duration, you don't need to worry about heatsinking the transistors. You will want to have monitoring to detect a shorted transistor. This is simply having pull down resistors at the rail outputs and ensuring that there is no voltage present when the high side driver is supposed to be off. Disable the ground (common) lines if there is a fault. You really should use relays for the ground switching. This gives you the mechanical air gap that a lot regulations require and if you do wind up firing multiple channels simultaneously, they can handle the required current. I'm quite partial to the T90 series from P&B as well as the EPE series from NEC. The EPE relay is really nice - 2 fully independent SPDT 30 Amp relays in a package about the same size as the T90. I have welded the contacts on those, however, when a screwdriver fell onto the PCB and shorted out the current limit stages. Again, fault detection is a good idea. In my units, a fault at the relay disables the current limit drivers and a fault in the current limit drivers disables the relays. Your choice of 24V is good. That is the only regret I have with our system - the client insisted that 12V was good enough when we were commissioned to design the system some 10 years ago. Now they use it with 400 foot long drop lines (outdoor stadiums) and the low voltage limits the number of devices they can fire on each cue. A future re-design will jump that to 24V. I had considered doing a 300V capacitor discharge version at one time but never did get around to it. Do let us know how you make out. Best of luck! dwayne Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 16 years of Engineering Innovation (1984 - 2000) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics