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Registered Member #477
Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546
Hello, coilers:
I've decided, at long last, to build a conventional SSTC. My driver is more or less a rip-off of Steve Ward's "Mini SSTC" driver, with a few extra protective measure sprinkled on top (which are, in turn, ripped off from a number of other people's designs ) However, I just realized that I don't undestand why Steve's design uses both a non-inverting and an inverting driver when there's an inverter IC sitting right there too (7414). Any takers? I'm tempted just to use two 37322's and derive the input for one from after both inverters and the input for the other from between them. This would seem nicer, because then there is only one kind of driver IC being used here, and I don't have to stockpile both kinds.
Perhaps some seasoned SSTC'er will tell me what nuance of the -21/-22 pair makes it better?
Registered Member #1024
Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95
The only benefit is that both are driven at EXACTLY the same time, adding another inverter, or taking one drive from an earlier inverter will add some ns delay. This is not a problem in my experience, and in fact there are often timing/drive differences in the inverting / non inverting gate drivers anyway. So you should be fine, but thats the reasoning behind it.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
If i understand the question right(which i highly doubt :P) The inverting and non inverting are both used because it gives 24 volts(assuming you use 12 volts input) through the gdt. This is good for making sure the mosfets turn completely on. I am probably wrong about something here, but i know that the inverting and non inverting are used for high gdt voltage.
Registered Member #618
Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628
The way I understand is like arc starter said the are tired together so that when the signal flips it acts like a 24v square wave but the reason for not using an inverter off the 7414 is because the uccs are HIGH current where as the 7414 is a few ma, which helps drive the gdt better then just using one of the spare inverters.
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I haven't checked the datasheets to confirm, but I doubt the delay in the inverting UCC and the 7414 buffer are much different. And you'll most likely be running a coil with fres of 200kHz??, in which case 15ns of delay is negligible. Unless your coil is HF and the delay difference may cause problems, you're clear to use the 7414 as the inverter.
Registered Member #477
Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546
Arcstarter wrote ...
If i understand the question right(which i highly doubt :P) The inverting and non inverting are both used because it gives 24 volts(assuming you use 12 volts input) through the gdt.
Sure, it makes perfect sense. However as I understand, the inverting IC is just like the non-inverting one except that it has an Schmitt trigger inverter (i.e., like in the 7414) integrated into it. I'm just wondering why that can't be factored out. You'd still get the 24Vpp.
Ken M. wrote ...
The way I understand is like arc starter said the are tired together so that when the signal flips it acts like a 24v square wave but the reason for not using an inverter off the 7414 is because the uccs are HIGH current where as the 7414 is a few ma, which helps drive the gdt better then just using one of the spare inverters.
I was talking about inverting the *input* to the *UCC*, and certainly wasn't suggesting feeding the GDT from a 7414 No siree! That would indeed not work.
Dylan wrote ...
The only benefit is that both are driven at EXACTLY the same time, adding another inverter, or taking one drive from an earlier inverter will add some ns delay. This is not a problem in my experience, and in fact there are often timing/drive differences in the inverting / non inverting gate drivers anyway. So you should be fine, but thats the reasoning behind it.
Uzzors wrote ...
I haven't checked the datasheets to confirm, but I doubt the delay in the inverting UCC and the 7414 buffer are much different. And you'll most likely be running a coil with fres of 200kHz??, in which case 15ns of delay is negligible. Unless your coil is HF and the delay difference may cause problems, you're clear to use the 7414 as the inverter.
Thanks, folks; that's what I was hoping to hear. Yeah, 200kHz is in the neighborhood. I probably should have spent some more time with the datasheets myself before asking
Registered Member #477
Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546
Steve Ward wrote ...
Sure, you could do it that way, no difference really.
Groovy, thanks, Steve. Just proceeding on the assumption that I'll be less likely to mess things up if I have fewer different kinds of building blocks; harder for me to get things backwards that way!
Banned on 3/17/2009. Registered Member #487
Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617
Or you could use two ucc27425 drivers in parallel. I started using these becase theres only one type of driver to buy, they're cheaper and I can get away with only using one if need be on the same board. I just don't populate one driver.
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UCC37321 and UCC37322 in Steve's "Mini SSTC" and other drivers.
) However, I just realized that I don't undestand why Steve's design uses both a non-inverting and an inverting driver when there's an inverter IC sitting right there too (7414). Any takers? I'm tempted just to use two 37322's and derive the input for one from after both inverters and the input for the other from between them. This would seem nicer, because then there is only one kind of driver IC being used here, and I don't have to stockpile both kinds.
No siree! That would indeed not work.
