High Side Driver

High Side Driver...

...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Jim Thompson
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Can you write something about this rather than just making a link-only post?

For how many years can you guarantee the above URL not to change?

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Reply to
Kaz Kylheku

Interesting, what defines the gate-source voltage of the high side device? The sim shows about 5V but I can't figure out why it that value. Would an external gate-source capacitor help combat diode leakage issues?

Reply to
piglet

Go to...

then click the S.E.D/Schematics button, and see a _somewhat_ complete listing of my posts (only about half of that page has been indexed).

Since it's my website... as long as I'm alive >:-}

Updated...

Now includes complete .CIR file (with all necessary device models), suitable for directly running in LTspice...

File/Open/HighSideDriver.cir

then select "Run" ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Jim Thompson

Sure, if you like flappy gates.

Also, who would buy an inductor when three BJTs does as well?

I did the inductor thing years ago, must've been like 2008ish. Plus a transformer:

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But I'd much rather spend a few cents and as many watts with a CCS turnoff than a few bucks inductor. Better still, just use H bridge drive (TL598).

Tim

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Seven Transistor Labs 
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Reply to
Tim Williams

Energy stored in the inductor gets dumped into the gate capacitance, which pulls the gate above the +12V rail. It's a little tricky to get the numbers right, to get the right overshoot but not risk blowing the gate.

The output can't stay up steady-state, because the gate voltage will decay and fry the fet.

Given a bunch of application-specific constraints, it works. It does waste about a half a watt in the resistor when you shut it down.

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John Larkin         Highland Technology, Inc 

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John Larkin

I guess you didn't observe the load current?

In general I'd guess your attention span is limited >:-} The need is for a high side driver, controlled by a 3.3V logic signal.

And the inductor is ~7 cents in the quantities used by my customer, and he's very cramped for space.

(In addition, schematic has been munged to hide details... customer only has +3.8V high-side supply, which must deliver 8 Amps to load with minimal drop.) ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Jim Thompson

I have a problem with Jim's pages, the lines are to thin to see, I suspect my reader, and will try adobe. How do I pull up associations? I've done it a dozen times but can't figure it out now. The reader I use is Foxit (I think, I find no identifying info) Thanks, Mikek

Reply to
amdx

The free Adobe X Reader seems to work just fine. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Jim Thompson

Thanks John, I got that. The circuit must be very dependent on the device capacitances and first mosfet switch-off rise time. I thought it a bit lucky gate drive was a nice 5V and not, say, 45V and droopy.

I wonder if inadvertently changing device vendors half-way through the production run may generate some excitement.

Reply to
erichpwagner

It was tweaked until it looked nice. Spice is great that way.

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John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
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John Larkin

Unless the device were terribly slow, the turn-off time has a miniscule effect.

Yes, it is nice and crisp.

It was calculated. Some of us here can do that, you know >:-}

Rude, crude and smug about it is the last stage in the "progressive" disease known as manic/depressive (aka Larkin's syndrome).

It proceeds downward from the mouth through the alimentary canal, ultimately resulting in loss of testicles.

In some extreme cases it has been known to cause total failure of the kneecaps >:-} ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

L = R^2 * C gets you in the ballpark, but the Miller capacitance and nonlinear things in the mosfet make it messy.

So, how did you calculate it?

Don't be absurd. The only thing to be depressed about is the pitiful amount of snowpack in the Sierras so far. I have a season pass at Sugar Bowl, and they are only half open. The fake snow wasn't bad last week, but the good runs off Disney and Crow's Nest are closed.

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You have an intense and enduring fascination with excretion and male body parts. Personally, I prefer food and female body parts.

kneecaps >:-}

What shape are your knees in these days? How's the skiing out there?

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John Larkin         Highland Technology, Inc 

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John Larkin

Could you care to elaborate on why you think the switch-off time is a significant contribution to this function?

Before you shoot yourself in the foot, think (and understand) fundamentals... we see so little of that expressed here :-(

Not a bit "lucky". It's easily calculated.

What's this "inadvertently"? And, supposing a gross change of device characteristics, it's trivial to adjust... WHAT to adjust is the question set forth to the student... hint: a fractional-cent device ;-) ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

You're wrong !-)

Since you got the answer wrong, you think about it for awhile.

I don't like cold. That's why I live in Arizona. And my knees are just fine... particularly for their most important task >:-}

And my BP is (right this instant) 117/68 at 74/min.

What's yours? ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

Missed that, last "round"... WHAT "Miller" ?>:-}

[You always amaze me at what you don't know :-] ...Jim Thompson
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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

You twiddled it in Spice.

Kneeling before customers?

Varies a lot. Relaxed, I get numbers like 115/75, but I'm seldom that relaxed. Exercize increases blood pressure; so does coffee.

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John Larkin         Highland Technology, Inc 

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John Larkin

NOPE. It isn't that you are ignorant. Far from it... it's just that you know so much that just isn't so. (Twisting a Reagan comment on Democrats) ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

If you calculated it, show us how.

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

Right click on the file and choose: 'Open With', then select 'Choose Program'. It will tell you what the default program is, and let you change it.

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Michael A. Terrell

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