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Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Daedronus wrote ...
I was always wandering, why not just use a pnp + npn totem pole made out of discreet components as a gate driver?
You can; right now I use a setup where I have UCC's driving some smaller IGBTs driving some brick gates - it gives you nice fast rise times and a very robust gate drive.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Daedronus wrote ...
I was always wandering, why not just use a pnp + npn totem pole made out of discreet components as a gate driver?
Yep, a discrete totem pole actually does surprisingly well driving smaller mosfets. Their main problem is that they require level shifting if you want to drive them from 5V logic, and even 12V logic gates might not have the power to drive them up to full.
My standard approach was to use a BS170 mosfet and a 100 ohm resistor in an inverter circuit to drive teh totem pole, but this might already turn a bigger hassle than simply using UCC's :)
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
Inducktion wrote ...
And, to revive a roughly month old thread; No one answered my question. ):
Well, I guess you probably could, but why would you want to? There are much more robust options such as the UCC chips, that are just as simple to implement and are actually designed for this task.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
You could use a high power opamp, but the performance would be pretty poor. Those opamps in particular have a gain bandwidth product of only 350kHz, so even if you wired it as a unity gain buffer and had no load on the output I would expect it to take a few microseconds to switch. When you start adding huge capacitive loads on the output it is only going to slow things down, so I would expect switching times in the 10-100us range for typical gate capacitances. You could probably speed it up a little bit by running it open loop, because at that point you have basically turned it into a gate driver
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
That L272 opamp you pointed out, while it's quite thruppy at 700mA output current, it's dog slow, only 1v/uS slew rate, not really quick enough to swing your gates around.
I was investigating high power output drivers for a product a few years ago, and came across the THS3091 (from texas at ti.com). I ended up using three in parallel to drive a 6v swing at 50MHz into a 50 ohm load with good distortion. The data sheet surprised me, because amonsgt the applications they suggested was FET gate driving. The output current is only +/- 250mA, but the slew rate is 7000v/us.
At $4 in 100s from the manufactruer (so probably double that in onsey/twosy from the distributors), would you want to spend that much when you can use a dedicated FET driver chip that can put out several amps, or build your very own thruppy totem pole from a couple of FETs?
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Could High power op amps be used as gate drivers?
