MOSFET GATE DRIVE?

8V-ish zener from gate to source. Best results would be with a turn-off resistor parallelling the zener, and a constant current drive (open collector with emitter degeneration or switched current mirror). Resistor depends on how fast you want it and how much current you can spare. You'll need some resistance no matter what, since the gate capacitance isn't going to fall too quickly through a zener in the "off" region, especially with leakage current from the driver keeping it on.

Tim

-- Deep Fryer: a very philosophical monk. Website:

Here is another delima....

I also have to be able to reduce the input voltage to a level that is acceptable for a small 5v regulator (max input voltage for it is 20v). A PIC micro is used to control the high voltage motor via some sort of drive circuitry. Like I said before, I have perfectly working setup that works with a 12-14 volt input source. The catch now is being able to allow up to 65 volts. This also needs to be all SMT and as small as possible.

I think what I need really is a way to reduce the incoming voltage to be less than 20 volts, and I need probably no more than 100ma of current for everything.

I am still looking at the idea of a zener diode/resistor voltage regulator. I believe I saw something with a transistor added somehow as well. Any thoughts?

"Jim Drew" a écrit dans le message de news:43ba9cf6$0$10240$ snipped-for-privacy@roc.nntpserver.com...

How about HIP4080/4081? Plus you'll only need N mosfets.

--
Thanks,
Fred.

I'll have to dig thru the 20 year old paper designs I did in that area...

Transformers driven PWM, with DC restorers on the gate side.

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Hello Jim,

One simple method is driving them via little toroid transformers. You just have to make sure that they cover the frequency range you are dealing with.

Regards, Joerg

Under your search engine, look up Half bridge drivers, some will work pass

100 vdc on the hi side, and two of them will form a full bridge driver. Some have a single input and some others have a hi and a low side drive input. They even have protection from turning a gate on if the other Fets gate is in the on position. Several kinds out there.

In article , Jim Drew wrote: [...]

Consider this:

V++ ! \\ / V++ \\ ! ! !!-- NMOS +----+------!! ! ! !!--+--/\\/\\/--+--------- Load 20V /-/ ! ! ! ^ ! B ! ! --------C E-------- GND NPN

You may be able to do without the current limiting circuit. You can make it slow start by putting a capacitor across the zener.

Beware that if you do both, you need a small resistor in series with the gate of the MOSFET. With no resistors near it, the MOSFET will look for a way to oscillate and fairly often find one.

--
--
kensmith@rahul.net   forging knowledge

Or, you can make it a bit more complex by adding a small power MOSFET like this:

SMALL GUY A S D !!------------ --------- -----+------!!- BIG FET ( ! ! ! ! !!- ( ------- \\ ! ( ! / ! ( ! \\ Large ! ( ! ! ! -----------+-------+---------+-----------

When the A point pulses high, the body diode in the small MOSFET conducts and charges up the gate of the big guy. If the transformer voltage then droops, the capacitance of the FET will hold the gate voltage for quite a while.

When the A point pulses low, the small FET turns on and the GATE of the big MOSFET gets discharged. If the transformer then droops, the gate voltage on the MOSFET settles back towards zero.

The resistor is only needed if you disable the drive completely. Leakages could cause the big MOSFETs gate to drift up.

--
--
kensmith@rahul.net   forging knowledge

[snip]

Turned out to be a cyst that burst.

We're just home from the surgi-center, lighter by ~$3K :-(

The joys of self-employment and $5K deductible ;-)

But I'm still ahead by ~$25K since I made that decision to risk a high deductible.

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

| 1962 | I love to cook with wine. Sometimes I even put it in the food.

You're NOT incorporated ??? Look up "Key Employees" ;-)

I was paying $900/month for $500 deductible.

Went to $500/month for $5K deductible... for the both of us.

I'm now just shy of 66, so I'm on Medicare... $261/month premium right now for the wife only. Next August the wife will be 65 and high cost will be over ;-)

"we are never sick" either... first claim in 6 years.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Hello Jim,

Such archaeological excavation can take a while. Had to do it a few months ago to find a really old filter design disk. It turned out to be easy, it was a thin 5 1/4 floppy tucked into the back of my CAD binder. Duh! But that didn't occur to me until after several hours of digging. I had all but forgotten that some floppy disks were indeed 'floppy'.

On many H-bridges that commutate regularly you can get away without DC restore. Sometimes I was even able to do it sans transformer, with just a coupling capacitor.

How's the spider bit coming? Did it heal a little?

Regards, Joerg

Hello Jim,

And they probably slapped you with full fare, like $40 per bandage where the HMO pays only their negotiated rate of $7 or so. But you belong to the part of society that plans for a rainy day and doesn't blow it all on fancy cars.

Well, your wife can now say that you spent $3k on her around Christmas time ;-)

At least we can now deduct the premiums. What's still not fair is that we must pay the 15.3% SE tax before deducting and employees don't. IOW we pay 15.3% more than they.

I am thinking about that as well. Right now we pay a little over $500/mo for two at Kaiser. Deductibles kick in mostly for hospital stays, $200/day or so but we are never sick. When I checked high-deductible plans they often aren't that much cheaper.

Regards, Joerg

[I was going to say something, but I promised :-]

Hospital and surgical only, no doctor visits.

Between the two of us we only have ~$200/month, so I think Part D is likely to be useless.

I did that in poison ivy ONCE... blisters everywhere, including everywhere I scratched :-( Potassium Permanganate gauze soaks for a week.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Rocks? Rocks? When I was a kid we used coal ;-)

(Tallmansville, WV, is just south of Philippi, WV, where my grandparents (on my mother's side) had a HUGE farm with their own seam of coal.)

Good point... I ought to see if my business membership at Sam's Club has any "benefits" ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Hello Jim,

We live in a blue state. What can I say? Like to keep it simple, no more bureaucratic layers.

Wow. I never saw a plan for us that would drop the premium by 40%. At least not for health care.

Then comes that drug plan with the mandatory donut hole. We do a lot of ministry and visitation in nursing homes. It's sad, many of those people had plenty of savings because of hard work and a frugal or at least prudent lifestyle. All it takes is a serious fall, stroke, whatever and you'll lose all that in a jiffy. $5k a month is nothing there and you still get jam packed into a small room with three others.

Same here. Except for rather stupid reasons like poison oak exposure. When we moved here I did not know what that was. So .... $45 of copay later I knew that I should have gotten out of those clothes right away and not finish up the brush clearing.

Regards, Joerg

Hello Jim,

Yes, I read something to that effect. That you and Win wouldn't throw snowballs at each other anymore. Or at least not with rocks in them.

But seriously, it's getting nasty here at times. I mean, when the owner of a perfectly healthy surfboard manufacturer throws in the towel that should say something to the local politicians. Unfortunately it didn't.

I'd be fine with that but the premiums are still so high. Probably because it's Kahlifohniah.

Don't know, depends on which meds you need. I have seen some really cheap plans. Even Walmart out here offered one.

Well, I waited so long that the doc said the rash migrated to the inside of my skin. Anyway, for the next season of poison oak removal he recommended "Tecnu soap" to wash down with right after the work and that stuff really does the trick for us.

Regards, Joerg