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what do you think of these bricks?

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Marko

Mon Aug 07 2006, 02:01PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Ward's brick driver uses a GDT, two mosfet's in halfbridge and capacitive divider, arranged 2/3+1/3 on isolated 45V supply.

ICL7667 (ward) or another mosfet (Conner) are solely used to keep dorsal mosfet on and gate at -15V.

I also tought if we could connect the GDT to '+' (drain of dorsal mosfet) so it is defaultly on while GDT is 'off'. Steve conner pointed out there will be trouble with such a drive, probably because voltage spike at end of cycle would open the mosfet and cause shoot-trough.

Two mosfets directly on GDT could probably be done using a P-channel mosfet, but it's usually simpler to throw a '7667 in.

Reaching

Mon Aug 07 2006, 03:42PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

mhh, okay, for the brick driver i thought about using this sheme

if i use this shematic should i look for some complementary mosfets or can i use any suitable mosfet? and for the supply voltage, what voltage should i choose, from the shematic i think less than 30volts, cause i dont want to go into trouble building a switch mode powersupply, simple transformer should do the same.

sorry, but im a complete noob in high side driving, .i understand the basics of this shematic but there are some things i dont understand .For example , why is the igbt emitter connected to pin 1 of the ucc gate driver? why is there a 30volt zener connected to pin 8 of the ucc driver, and i wonder about the 9,4volt zener on the 2200yf cap..some people out there who can explain it a bit?

williamn

Mon Aug 07 2006, 04:34PM

Registered Member #55 Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149

I have used Steves newest highside Gate drive circuit now a few times, I added a few things like undervoltage lockout but basically its a bastard of Steves circuit. The Zeners act as voltage regulators, the capacitive dividers form the grnd reference point and inturn provide + and - voltage rails. You can use a plain old 60/50hz transformer to power the circuits, for my big coil I did exactly this, I just made 4 isolated windings on a large laminant core, it was 120VAC:36VAC(4) resulting in 50volts on each circuit after their own fullwave rectifiers. I also have used a simple 20watt SMPS using a 50% dutycycle squarewave source (any type works, I used a 555) running at about 50Khz, TC44xx gatedrivers, gdt and simple halfbridge of cheapo mosfets. It works well and is much lighter than the heavy core transformers. This is a really good and simple gate drive circuit.
BTW here is a picture of the transformer I built, apparently my cat decided at the last second to make his opinion of my workmanship known.

1154969656 55 FT1630 Gate Driver Suppy Xfrmer

Reaching

Mon Aug 07 2006, 04:56PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

okay, seems like the circuit works reliably, i made a board layout in eagle which fits perfectly on the bricks with all parts on it, except the 1:1 signal transformer.. but 50volts dc? i thought about 30volts dc or so, the 30volt zener will conduct all the time on 50volt input , what voltage is on the ucc driver ic? i hope nothing more than 15 volts.mhh, i have to give it a try, . . what type of p channel and n channel mosfets did you use?, i have no idea but i made my pcb with to220 devices, so any help is welcome.

williamn

Mon Aug 07 2006, 05:18PM

Registered Member #55 Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149

With load the voltage dropped to approx 45VDC which meant +30VDC and -15VDC. I use a 15V zener for the negative rail regulation. The mosfets where sampled from On and where
MTB30P06VT4G
NTB75N06T4G

Steve Ward

Mon Aug 07 2006, 06:35PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Ok, some key points with the brick driver. To get the ultimate, super fast drive, use small mosfets. I used some small fets from fairchild, the Pch is rated 11A at 60V, and the N-ch is 13A at 60V. Look for fets with the smallest gate charge, but are still in the ~10A range!! This will result in a much faster driver than if you put in big monster 60A fets or something (using such large fets does not have any merit). The fets dont need to be a matched pair to work, but try to find a pair that have relatively similar ON/OFF times, gate charge, and current ratings.

Power supply issues. If you want the +30V, -15V drive, you will need a total of 45V, and then use a resistive divider (or you *could* rely on zeners to divide it, i actually use both) to get a -15V supply and +30V supply. The gate driver chip is powered from the -15V supply, so the "ground" pin of the chip is tied to -15V while the Vcc is tied to "0V". This puts a positive 15V on the chip, as required. The 15V and 30V zeners limit the -15V and +30V supplies as necessary. I suggest using 5W devices.

You must use an INVERTING driver so that when the input signal is low, the bottom fet gets 15V on it, turning it on, and pulling the IGBT gate to -15V when the coil is off between bangs.

The p-channel fet is driven through the .1uF capacitor, i got this clever trick from Jimmy. This inherently limits the maximum ON time of the IGBT due to the 1k resistor eventually draining the charge from the .1uF cap (and the Pch gate capacitance). But typically this time is considerably longer than you would ever operate at normally.

Reaching

Mon Aug 07 2006, 09:00PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

ok, you helped me a lot, i ordered some parts and when they arrive i can start building the drivers. i nearly finished the low inductance wiring, heres a pic

, i have some more double sided pcbs which i want to use for the middle contacts, then a layer of 2mm copper sheet or so, will see.

for the mosfets i ordered some irf530n channel and some irf 9530 p channel mosfets, both are 100volt 14,12A have a gate cap of around 800pf, the n channel is faster than the p channel, but that was what i found, hope that works

Marko

Mon Aug 07 2006, 11:21PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

This driver is what I talked about 'with P-channel mosfet's.

It's input is designed ot be easy-to-drive, but if you want, you can simply use some standard UCC-driver board and drive MOSFET's trough a GDT with it. GDT would only need to be small driving a simplepush-pull of mosfet's recommended by steve.
Tons of conbinations..

Steve Ward

Mon Aug 07 2006, 11:23PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

The 530 and 9530 should work just great.

Looks like you are off to a good start. You plan to eventually add copper to the PC board for the bridge, right? I dont know that the clad alone will handle the currents. Im using some pretty thin copper for mine, i think its about .5mm thick. To solder it down, i first put little "beads" of solder down on the clad board. A blob of solder every 1-2 square inches is enough. Then get out a propane torch, set it for low flame, and slowly heat up an area of the copper until the beads of solder melt underneath. When you get it to the right temp, you can see solder flow along the outer edge of the copper (similar to if you have done plumbing work, when you "sweat" the pipes). I got my copper sheeting sold as roof flashing at the hardware store.

Oh, and i wanted to mention, there is probably no need to go with more than the 2 x 12000uF caps. 4 of the caps is more energy storage than you really need and may actually lower your power factor somewhat.

Reaching

Tue Aug 08 2006, 04:35AM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

okay, thanks steve, ,
the upper and lower power rails are finished as you see in the pic, there is a double layer pcb first and then a 2mm thick brass sheet screwed on it, that is what i want to do for the wiring in the middle, with some thick screws to connect the primary on it. in a few days i can test the bridge to see how far it goes i hope for a fres of around 50khz, . i calculated some secondaries and came upt with a 8"x40" Former wound with around 0,3 or 0,4mm wire, with a big enough toroid this will give me a resonant frequency of around 48khz, low enough i think, and big enough to create some really long bright power discharges

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