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Registered Member #1381
Joined: Fri Mar 07 2008, 05:24PM
Location: Hungary
Posts: 74
For some time now, I started working on my first drsstc project. The H-Bridge section is completed. (upcoming topic in Projects soon) So now im working on the driver sections. Been testing Steve's "brick driver" , but there were a lot of oddities (some cause at first i was trying to measure the floating outputs , by connecting one end to ground... silly me) like the the ucc's/tank cap's voltage drops below 4V from 8-9V (after a few cycles) so it stoped functioning and the fets kinda latched up or something similar , also for some the reason the input signal after the 1kohm was only 1/10th the input , after removing it that "latch up" problem seemed to be solved.
So as of now i think im on the right track , the other problem is that the end resistor still dissipates alot of power , is this normal? (currently a 22ohm 11W ,after 20-30sec it gets really hot, ghessing 80-90°C)
other specs: 10V and 20V zeners, irfp540n(n mos) , irf9540 (p mos) , around 24 Vin , input signal: 12V from PWM ic
Scope screen: Ch1: V gate , Ch2: V emitter CHmath: ch1-ch2
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Its probably a bit too late, but i *just* published my latest "brick driving controller"
Its basically just a beefy version of my older controllers, and i took care to wind the GDTs better and do some other things better. Ive since replaced my old high-side gate driver stuff.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
What was your selection criteria that drove you to use the ST MOSFETs in the D2PAK SMT package?
1) Money 2) low Qg 3) fast switching time
Also, how difficult was it to solder the drain (case tab) to your PCBA? How good of a low-thermal-resistance junction do you think was achieved?
Not difficult to solder at all. I went SMD to get a low inductance layout. I dont really care about the thermal impedance since the pads are only the size of the mosfet anyway, mostly just after good electrical connection. This drive runs far cooler than other gate drive chips because the Rds ON is much lower comparatively.
You may notice im using 9V to drive the MOSFET gates. My testing showed optimal results at about 8V, so i figured i should give it just a tad more to be safe. I was optimizing propagation delay and cross-conduction. The total propagation delay for the UCC37323 and the MOSFETs is 50nS, about the same as an IXD type driver from IXYS.
Also, do you have any information in the ferrite composition used in your GDT core?
Ive used a few cores of unknown materials. I have also used type 77 material from amidon, as well as type 5000 material from TSC international. Something with a permeability of 5000 or so seems to work just fine. Most of the toroids ive used were about 2.5" OD, pretty hefty compared to what most of us usually use. Reason for the huge ferrite is simply to fit all that multiconductor cable through there, and because i had quite a few of this big toroids around .
Registered Member #76
Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458
Nice one steve. But,,, why did you use a ucc27423 instead of ucc27425 which is one inverting, one non inverting? that would have been much easier.
one other thing that made me stuck. these smd capacitors on the output. i never thought that smd caps can handle this currents flowing through the output of a mosfet bridge driver circuit like this, even with a 10R resisor in parallel? Why is it there?
the next thing, why can you invert the incoming interrupter signal with jp2?
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
But,,, why did you use a ucc27423 instead of ucc27425 which is one inverting, one non inverting? that would have been much easier.
Because i want both N-fets to turn ON after the burst ends so that the GDT primary is firmly clamped at 0V across it.
one other thing that made me stuck. these smd capacitors on the output. i never thought that smd caps can handle this currents flowing through the output of a mosfet bridge driver circuit like this, even with a 10R resisor in parallel? Why is it there?
I dont seem to have any heating issues with these 10uF 1206 SMD ceramics, and they dont seem to have too much ESR either, perhaps i can try to measure it later. The 10 ohm resistor is to aid in damping the ringing that occurs when the GDT is turned off at the end of the burst. If there is DC bias and saturation (say if there is no feedback, you just get a big pulse at the output) the 10 ohms is enough to limit the current to something reasonable. Also, the P-fets are capacitively driven, so they will automatically turn off if there is an extra long pulse applied to them. Its admittedly not the cleanest solution, but it seems quite robust so far. I use it on a dual CM300 bridge for 10-12 foot sparks, and a single CM300 bridge for 5-6 foot sparks. No failures of any sort on either driver.
the next thing, why can you invert the incoming interrupter signal with jp2?
The inversion is optional. My fiber optic receivers are inverting output, so that is why i did this.
Registered Member #154
Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260
Hi Steve,
Just want to ask....is your OCD feedback input drawn correctly? the reason i ask this is that normally in your other circuits, it feeds a bridge rectifier of 1N4848 diodes.....if that is still the case, is the input to the bridge drawn right?
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Brick driver issue
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