Any logic-level FETs with breakdown 300V+?

Bipolar? Darlington?

John

how about that ?

I've no idea, but seeing what will happen to the rest of the system if one fails d-g, I'd be tempted to opto isolate it. I've seen PCBs with a big, brown- edged hole where the electronics used to be.

that have a guaranteed Rdson of around 1ohm or less

tables. The usual ones are only rated at 10V

drive voltages at lesser current. But the

is like kicking a big oak tree.

too much money plus it would need its personal supply

Pretty nice. Now does digikey stock them? :)

Have not noticed any (though there are a few 200V small MOSFETs rated for logic-level drive, but higher Rds(on) and lower current rating than you want.

OTOH, you'll have thousands of inexpensive jellybean choices if you make it 10V drive.

Best regards, Spehro Pefhany

Way too slow. Most have turn-off times in the usec range. Sure, you can hold them a wee bit above saturation but then circuit complexity begins to eat real estate and pennies.

Like usual, Rdson max only guaranteed at 10V and the transfer characteristic looks rather spooky. It's most likely going to explode if you try to switch heavy loads at 5V:

We are fuse-protected :-)

Yeah, which is what we'll do. I was just hoping. 10V drive will add a lot of stuff and we are really cramped for space on this one.

I wish there were fast BJT under 15c with hold-off Schottky built in. Is there still time to write to Santa ...?

Silly me, I should have know that speed was important here.

John

Sorry, should have mentioned that.

Does the drive need to be truly DC-coupled? You could maybe do some cute stuff if the fet doesn't have to be on for a long time.

John

I could but then the transformed-up Cgs would hit us from behind. Looks like we might have to provide a clean and staunch 10V.

A two-stage solution (N channel pulling a P channel to ground) is out of the question?

Requires dead-time control (+8 parts) or we'll run a chance of sitting there at the EMC lab with egg in our faces.

that have a guaranteed Rdson of around 1ohm or less

tables. The usual ones are only rated at 10V

drive voltages at lesser current. But the

is like kicking a big oak tree.

too much money plus it would need its personal supply

Mouser has them. :)

And why can't you use a charge pump inverter source on the driving side for the gate? I've done that before using simple things like a PNP for high side to drive the gate via a charge pump inverter and common on the low side via a open collector NPN drive.

It works perfectly, since the charge pump reservoir cap has more than enough to over come the Cgs on the gate for the initial transition. You may also consider a low value R in series with gate to avoid parasitic noise, like ringing for example. Many times board design can over come this how ever, it does not hurt to through in a 1..10 R.

Or, just use a ready made gate driver chip with the same characteristics.

USELESS.

VGS(th) Gate Threshold Voltage VDS = VGS, ID = 100 uA 3V min 3.75V typ 4.5 V max

Do you suggest Joerg selects them ?

Graham

Jesus christ.. You got to be kidding me.

That fits every spec he was looking for with the exception of the gate voltage for which, is the simplest thing to work around. Which is why they make charge pump drivers in cases like this..

Yes, it adds a little extra to the component count how ever, this has been answered many times with various types of gate drivers.

This is 101 design techniques around FETS. Gate voltage in most cases is the smallest issues.