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PICList Thread
'[EE]: Power MOSFET driver'
2002\02\26@080630 by Edson Brusque

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Hello,

   inspired by the recent thread about "Switching low voltage AC", I'm
returning to the development of a solid state relay using MOSFETs.

   I'm trying various configurations of MOSFET drivers, but what I really
need is a schmitt trigger with some mA capabilities. A schmitt trigger can
be done with an op-amp, but the slew-rate of the opamps I know can swing to
GND and VCC is very slow.

   Any sugestions?

   Thank you very much,

   Brusque

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2002\02\26@081116 by mike

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On Tue, 26 Feb 2002 10:02:57 -0300, you wrote:

>Hello,
>
>    inspired by the recent thread about "Switching low voltage AC", I'm
>returning to the development of a solid state relay using MOSFETs.
>
>    I'm trying various configurations of MOSFET drivers, but what I really
>need is a schmitt trigger with some mA capabilities. A schmitt trigger can
>be done with an op-amp, but the slew-rate of the opamps I know can swing to
>GND and VCC is very slow.
>
>    Any sugestions?
Use a comparator instead of an op-amp. op-amps do not make good
comparators in many cases.

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2002\02\26@081704 by Vasile Surducan

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cmos       : CD4093
ttl        : 7413 or equivalents
comparators: LM393, LM111
discrete   : two transistors

The slew rate does not count too much because any schmitd trigger designed
with operational amplifiers use the comparator structure ( positive
feedback ) which increase the slew rate.

Vasile

On Tue, 26 Feb 2002, Edson Brusque wrote:

{Quote hidden}

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2002\02\26@102802 by Edson Brusque

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Hello Mike and Vasile,

>Use a comparator instead of an op-amp. op-amps do not make good
>comparators in many cases.

   what I don't like about the comparators is the open-collector outputs.
As I'm implementing an auxiliary power supply with resistor-zener
regulation, I have to stay low current.

> cmos       : CD4093

   Very good sugestion! I'll this today.

> ttl        : 7413 or equivalents

   Vmm, only 5V I suppose. I need 10V minimum.

> comparators: LM393, LM111

   Open collector.

> discrete   : two transistors

   I've thought of using a pair of TO-92 MOSFETs (BSS100/BSS110) to
implement a driver that could help to sink/source current to the high power
MOSFETs gates.

   I've learned today that Fairchild makes some optocouplers (MOC5007/8/9)
with schmitt trigger outputs that could have VCC as high as 16V. I would
like to try these ones, but they're open collector too...

   Thank you very much,

   Brusque
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Researcher and Developer               Blumenau  -  SC  -  Brazil
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2002\02\26@145908 by Jinx

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ICL7667

http://www.intersil.com/Data/FN/FN2/FN2853/FN2853.pdf

Schmitt, fast, and can also level shift from 5V to 12V. I've
used it with PWM and 80A FETs, love it

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2002\02\27@014316 by Vasile Surducan

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On Tue, 26 Feb 2002, Edson Brusque wrote:

> >Use a comparator instead of an op-amp. op-amps do not make good
> >comparators in many cases.

 The greatest mistake that many people do, is unknowing the extraordinare
advantage of an operational amplifier used as comparator against a classic
open colector comparator, OA will have a smallest offset and the slew rate
can be increased by supressing any lad and/or lag capacitor correction. In
fact any phase correction must be avoid when OA is used as comparator.
Whith this rule any fast OA become the best comparator. A good example of
how to don't design a comparator is the internal f62x structure which have
an offset greater than many common operationals and required some
histeresys for a nice switching.

best, Vasile

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2002\02\28@102823 by Edson Brusque

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Hello Jinx,

> ICL7667
> www.intersil.com/Data/FN/FN2/FN2853/FN2853.pdf
> Schmitt, fast, and can also level shift from 5V to 12V. I've
> used it with PWM and 80A FETs, love it

   very interesting chip. I've requested some samples. I'm trying to find a
similar chip with no-inverted output but haven't found any.

   Thanks,

   Brusque

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Edson Brusque                 C.I.Tronics Lighting Designers Ltda
Researcher and Developer               Blumenau  -  SC  -  Brazil
Say NO to HTML mail                          http://www.citronics.com.br
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2002\02\28@114920 by smerchock, Steve

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Brusque,

Check out MICROCHIP's (TELCOM SEMI.) MOSFET drivers.

www.microchip.com/1010/pline/analog/anicateg/power/pwrmang/mosfet/ind
ex.htm

I have used them before and they work very well!!

Steve

Steven Kosmerchock
Radio Frequency Systems
Phoenix,  Arizona  USA
(WORK) http://www.rfsamericas.com

http://www.geocities.com/researchtriangle/lab/6584

"Great spirits have always encountered violent
oppposition from mediocre minds."--A.Einstein

{Original Message removed}

2002\02\28@151925 by Jinx

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> Check out MICROCHIP's (TELCOM SEMI.) MOSFET drivers.

Nice tip, thanks

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2002\02\28@153141 by Jinx

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> > ICL7667

> similar chip with no-inverted output but haven't found any.

I never did either. I put a 74ACT132 gate (NAND Schmitt) in
front of the 7667 to keep logic levels true

===============================================

I've often wondered about why Schmitts are only available
as inverters. If you look at the internal block diagram of a
4093 for instance you see it goes

NAND >> non-inverting Schmitt >> inverter >> inverter

If they left off the last inverter you'd have a non-inverting Schmitt

Does anyone have an idea why they can't do this, given that
the flow diagram shows a non-inverting Schmitt gate exists
on the chip ?

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2002\02\28@170659 by David Minkler

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Look at TI's TPS281X mosfet drivers (or the Unitrode UC370X family
acquired by TI).  Available in most any flavor you'd care for.

Regards,
Dave

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