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Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Finn Hammer wrote ...
Goodchild wrote ...
In simulation it looks to me like the voltage out of the phase lead network has significantly less phase lead than then when it's at a higher input current. Consequently it doesn't even look like you get any lead until the second half cycle. After the first half cycle the amount of lead doesn't seem to change much with input current, it stays rather constant.
I'm not supper worried about the first cycle ringing, I have lived with it sense I started using phase lead. I'm just a little OCD about electronics, and if I can make it perfect I must try!
Eric,
That simulation is consistent with what I saw when I initially pioneered the phase lead circuit, and it does indeed seem as if the current monitor doesn´t produce any lead before the first reversal. All my Predictors did this.
Great idea, I was thinking of something along those lines. My initial thought was to have a flip flop momentarily change the comparator reference voltage on the first cycle and then return back to normal after the first half cycle.
Registered Member #205
Joined: Sat Feb 18 2006, 11:59AM
Location: Skørping, Denmark
Posts: 741
Goodchild wrote ...
Great idea, I was thinking of something along those lines. My initial though was to have a flip flop momentarily change the comparator reference voltage on the first cycle and then return back to normal after the first half cycle.
An even better idea, since it is simpler, and simplicity rules!
Registered Member #8435
Joined: Sun Dec 02 2012, 04:29AM
Location:
Posts: 5
If Eric doesn't mind, I'll print up a bunch of these boards and get sell them off here - it's cheap to get a bunch made but kind of expensive for just a couple. I build flight control boards for quadcopters right now and have a pretty good deal with a fab that I can stick a few extra boards in for the next run.
Edit: Hmmm, I have only one post now, haha. I think my account got deleted after being inactive for a few years (I'm sure some of my old posts still exist back on the old server somewhere)...
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Hi Eric. Just curious, do you use gate resistors anymore with these UD drivers? I just did some preliminary testing with using 5.1ohm gate resistor (typical I've used in the past) and the gate waveform was way overdamped so now I'm going to try without gate resistor.
EDIT: Seems I fixed my own problem with 1.1ohm gate resistor
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Question about the phase lead: say I calibrate my PL at around 300-350V (my oscilloscope is catII 400V max, dont wanna damage it), will it change at all or make any significant difference when I operate the coil at full voltage around 650-750V? I read something on TCML that said as voltage increases, the ringing will tend to be less and less, but somehow this just doesnt make sense to me.. I'd figure that the ringing would increase or stay constant with the voltage.
EDIT: Also when I was messing around with the phase lead and looking at the waveforms, I could not diminish the ringing on the second and third transitions no matter what inductor I used and how I adjusted them. but all other transitions always had no ringing and the transitions occurred exactly 1uS after zero crossing and no amount of adjusting several inductors could change that. Does that sound right to those more experienced with phase lead?
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Firebug24k I was planning on doing a bulk buy on the boards some time in the near future, but if you want to do the same it's fine with me.
Lets start with the gate resistors, yes they are still needed for a couple reasons; one they help prevent overlap in the transition of low and high side switches so you don't get shoot-through currents. Also they helps drown out ringing on the gates due to parasitics in the GDT secondaries from leakage inductance.
Generally what you want to do is adjust the phase lead so you only have the spike on the first or second cycle and non of the others. This will gets smaller with higher currents. The reason is that during the first cycle the voltage is not high enough to trip the comparator early, as a result it switches late. However as current in the primary increases so does the feedback voltage and at a point it will start leading the correct amount.
This is a controller quark and not one of the H-bridge or power electronics. As we talked about on the other page this first cycle ringing is not much of an issue due to the current on the first cycle being very low (this means low losses). One way to help this issue is to use schottky diodes in place of the 1N4148 in the feedback chopper network. Due to their lower voltage drop they start to conduct sooner at the lower feedback voltages and helps increase the lead on the first cycle. (same diodes as used in the OCD rectifier work fine)
I was thinking of fixing this issue with a Flip-Flop, that changed the reference on the comparator for the first cycle. However I'm not sure the added complexity is worth the bonus you get when it's really not that big of a deal to begin with. Maybe in the future I will add this feature for the supper "OCD" coilers (such as myself) that need to have their waveforms perfect.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Nice idea for a future UD 3!
So after reading what you said I went back and fiddled with the phase lead some more. Just like you said, the ringing on the first and second cycles noticeably decreased when I exceeded 350V on the bridge and about 650A in the primary, whereas I originally did tests at around 250V. Thanks for clearing that up! I'm surprised still! Would have thought the spikes would increase... Below is the best I could get it.
Does that look good, fine, bad, acceptable? I'm hoping It's not too much lead. Compared to other waveforms I've seen around the web, I think this is OK
Registered Member #8435
Joined: Sun Dec 02 2012, 04:29AM
Location:
Posts: 5
Goodchild wrote ...
Firebug24k I was planning on doing a bulk buy on the boards some time in the near future, but if you want to do the same it's fine with me.
Update - boards came in! They look great. Twelve bucks each, including shipping anywhere in the US. Shoot me a PM if you want one, or you want me to figure shipping elsewhere outside the USA. I built them exactly from the schematics Eric put out, no changes.
Anyone got a nice SOT-227 half-bridge/full-bridge layout PCB made up? I'll trade you one of these for a copy of those files, my layout skills are pretty poor :)
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Universal DRSSTC Driver V2.5 (Sold Out)
