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inverted cmos?

I need to use cmos + invert the signal. I tried to put the nch mosfet on top and the pch on bottom. This does work except the output does not swing rail to rail. I assume this has to do with the finite resistances in the mosfets?

I think it will work for my app because I have a few volts to spare on my rail and these will be driving a power mosfet. My rail is 12V so I'll still get pretty decent gate drive voltage. Is there any other problems with this?

Essentially either I have to use and inverter + cmos or use this combination to get the inversion and cmos that I need. I'm trying to minimize the number of components and if I use a cmos inverter then then thats 4 instead of 2.

Actually I need noninverted drive and inverted drive to drive two seperate mosfets, one a pch and the other an nch(in an h-bridge). the pch needs to be inverted so I can just use one cmos. the nch doesn't need to be inverted but needs to be driven so that requires two cmos inverters or this "inverted combo" I'm talking about.

VCC | ||--/ ||

Reply to
Jon Slaughter
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Try p on top and n at the bottom

Reply to
sprocket

Jon, Trying to make sense of your drawing... You've shown a complementary follower, albeit in CMOS. Is that what you want? Bipolar would be better.

...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     |
             
         America: Land of the Free, Because of the Brave
Reply to
Jim Thompson

No, it has to do with a possibly large Vgs required to make the FET turn on...this subtracts from the available output voltage.

It is much simpler to use a well-bypassed MOSFET gate driver IC, available in inverting and non-inverting, they don't cost all that much, minimize the component count, and they drive the hell out of your power MOS...

Reply to
Fred Bloggs

You didn't get it at all.... ;/

Reply to
Jon Slaughter

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

hehe

Its just cmos with the n chan on top and p ch on bottom.

I'm not sure what a complementary follower is though. BJT would work better here but of course requires more setup?

Reply to
Jon Slaughter

I know but thats not what I asked. I have ordered a few drivers but thats not the point. (Although the drivers seem quite expensive for some reason ;/ More expensive than the damn H-Bridge I'm trying to drive ;/)

What I really want is a driver specifically to drive an H-Bridge with one pin for turning on the high and opposite low side and one pin for switching H-Bridge sides(for reverse). I haven't seen these yet so ;/ Maybe even some type of emergency shut off pin which all mosfets stop conducting(or you could call it an on/off pin).

Reply to
Jon Slaughter

So build it discrete. I count what, four generic NPN/PNP's?

Tim

-- Deep Fryer: A very philosophical monk. Website @

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Reply to
Tim Williams

A complementary follower is what you drew. You _are_ a designer ???

...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     |
             
         America: Land of the Free, Because of the Brave
Reply to
Jim Thompson

Its a bit more than that but you need resistors too. There is much more power loss. Actually I did do it using BJT's but not sure if I want to waste the power which is why I was looking at the cmos method. The cmos version is a little easier to layout and much more efficient except that the inverted cmos idea. Obviously if I have to use two cmos inverters for the n ch's then its not worth it which is why I asked the question about the inverted cmos.

To get the 1A gate drive I need(or at least what I'd like), I'd have to use at most a 12 ohm resistor(thats 12W's too at 12V). This resistor will be conducting the half the time(or half but there are 2 that are complementary). Thats a lot of power wasted for no good reason.

Reply to
Jon Slaughter

I'm self taught so it really depends on what you call a designer. But I can't seem to find anything about a complementary follower(except stuff on a few patents and DIY audio) when searching google.

(unless you mean that they are in source follower configuration and also complementary? If so that doesn't mean much w.r.t what I asked)

Reply to
Jon Slaughter

use

Uh yeah, that's why you _don't build it class A_. Easy enough to fit eight more BJTs on the board, two right beside each MOSFET. SOT223 takes up as much space as, what, the 1/2W resistor you're probably using for the gate?

"Complementary emitter follower" ring a bell? Works a whole heck of a lot better than an unbiased complementary source follower -- hysteresis band is a nice and stable 1.4V, not something undefined between 4-8V. Or worse, -4 (short circuit!) to +4V if one were to cheat with low level MOSFETs (Vgs(th) ~ 0V that is).

Tim

-- Deep Fryer: A very philosophical monk. Website @

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Reply to
Tim Williams

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