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'[EE]: Power FET design application notes'
2001\02\25@022454 by Russell McMahon

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Some excellent power FET application notes from  International rectifier.
Cover many basic but important aspects of power FET design    .

       http://www.irf.com/product-info/hexfet/hexfettech.htm

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'[EE]: Power FET design application notes'
2001\03\01@142259 by Edson Brusque
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Hello Russell,

> Some excellent power FET application notes from  International rectifier.
> Cover many basic but important aspects of power FET design    .
>         http://www.irf.com/product-info/hexfet/hexfettech.htm

   I'm looking for a circuit that receives TTL signal (0-5V) to turn on-off
a high-power-FET that's switching at 100-240V.

   Do you know where can I find some squematics?

   Best regards,

   Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
(47) 323-2685  /  (47) 9993-6453
Blumenau  -  SC  -  Brazil
http://www.citronics.com.br
-----------------------------------

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2001\03\01@143710 by Eisermann, Phil [Ridg/CO]

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What is the load you are switching? How fast do you need to switch it? are
you switching the high side or the low side? In other words, is the fet
between power and load, or between load and ground? or is it more
complicated than that? We need some more information.


{Original Message removed}

2001\03\01@170049 by Edson Brusque

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Hello Phil,

> What is the load you are switching?

   basically lamps. 220V x 100W or 110V x 100W. AC or pulsating DC
(rectified AC, without the capacitor usually used).

>How fast do you need to switch it?

   I'm thinking in 20-30kHz

> are you switching the high side or the low side?  In other words, is the
fet
> between power and load, or between load and ground? or is it more
> complicated than that?

   I'm not switching yet because I don't know how to make it. :)

>We need some more information.

   Just ask.

   Thank you,

   Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
(47) 323-2685  /  (47) 9993-6453
Blumenau  -  SC  -  Brazil
http://www.citronics.com.br
-----------------------------------

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2001\03\01@170926 by Olin Lathrop

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>     I'm looking for a circuit that receives TTL signal (0-5V) to turn
on-off
> a high-power-FET that's switching at 100-240V.

There are chips that do this called "high side FET driver".


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, .....olinKILLspamspam.....embedinc.com, http://www.embedinc.com

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2001\03\02@170035 by Eisermann, Phil [Ridg/CO]

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Well, switching the lamps should be easy enough. You're just switching them
on and off, yes?
In this case, I'd be tempted to go with BJT transistors instead of MOSFETs.
There's really no reason to use a MOSFET to switch the lamp, and the drive
circuit will be easier. You're not going to try dimming these with the FETs,
are you? Anyway, here is a sample schematic for driving your FET:

             +12V                  +Vdc
               |                     |
               C                     |
           +--B   (Q1 NPN)          LOAD
           |   E                     |
           |   |                     D
Vin --RRR--+   +---R2R2R2---+-------G  (Q3 FET)
           |   |            |        S
           |   E            K        |
           +--B  (Q2 PNP)   A (ZENER)|
               C            |        |
               |            |        |
              GND          GND      GND

       Q1 and Q2 form what's called a totem-pole driver. something like the
old 2N3904 and 2N3906. Or 2N4401 and 2N4403. They help ensure the MOSFET
gate is turned on quickly by providing more gate drive than your PIC could.
size the resistor 'RRR' as normal for a PIC-to-transistor interface. You
might want to use a pulldown resistor on the bases of Q1 and Q2 to avoid
floating them if you tristate the output pins of the PIC. *NOTE* Q1 and Q2
are powered by +12V, not +5V. It doesn't have to be exactly +12V, but it
should be at least +10V. Since you are using it as a switch, you need to
ensure that the gate of the FET has enough voltage to fully turn on. I often
use the unregulated power from the +5V logic (eg before the regulator). The
supply voltage for Q1 should not exceed 20V, however. That would destroy the
FET. The resistor 'R2R2R2' and zener diode are there to prevent ringing at
turn-on and ensure the gate voltage does not go above 20V. This resistor is
usually 22 Ohm to 100 Ohm.

       I'll be out of the office all of next week (going to Europe), so i
won't be able to respond to any questions. I hope this gets you started.
Someone posted some links just a few days ago to International Rectifier's
appnotes on power FETs. I suggest you check those for further help.

{Original Message removed}

2001\03\03@094353 by Russell McMahon

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Unfortunately, the example FET driver circuit given would not work with a
PIC.
The input would have needed to swing a full 12 volts and the PIC will only
swing 5 maximum.
Also, there was a pullup resistor missing.


The circuit below fixes this problem, uses only one more diode and works
extremely well in practice.
Use a constant width font to view this diagram if it is scrambled in your
browser.
(eg paste into notepad or use Courier font in Word)


           /===|===  +12V           +Vdc
       R3  R   |                     |
           R   C                     |
           +--B   (Q1 NPN)          LOAD
           |   E                     |
           |   |                     D
           |   +|---R2R2R2---+-------G  (Q3 FET)
    Diode1 |-KA-|           |        S
    r1     E                K        |
Vin-RRR-+--B  (Q2 PNP)       A(ZENER) |
           C                |        |
           |                |        |
          GND              GND      GND

Operation is similar to the previous circuit.
Q2 and R3 provide a full voltage swing (here = 12 volts).

Diode1 (typically 1N4148) provides a gate turn off path for the FET when Q2
is on.
When Q2 is off the base of Q1 is oulled high by R2 and drives the FET gate
high.
Typically
R1 = 1k to 10k
R3 = 1k to 10k

R2 = 47 ohms to 470 ohms.

In practice for slow turn on / turn off devices all you need is a level
shifter.



         +12V                       +Vdc
       R3  R                         |
           R                         |
           +                         |   LOAD
           |                         |
           |                         D
           |-------R2R2R2---+-------G  (Q3 FET)
    Diode1 |                |        S
    r1     E                K        |
Vin-RRR-+--B  (Q2 PNP)       A(ZENER) |
           C                |        |
           |                |        |
          GND              GND      GND


BOTHY drivers are inverting.
ie a high input turns the FET OFF.




regards



 Russell McMahon

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2001\03\05@092531 by Eisermann, Phil [Ridg/CO]

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Russel, thanks for catching that. I knew I forgot to add the level shifter.

-----Original Message-----
From: Russell McMahon [apptechspamspam_OUTCLEAR.NET.NZ]
Sent: Saturday, March 03, 2001 3:01 AM
To: @spam@PICLISTKILLspamspamMITVMA.MIT.EDU
Subject: Re: [EE]: Power FET design application notes


Unfortunately, the example FET driver circuit given would not work with a
PIC.
The input would have needed to swing a full 12 volts and the PIC will only
swing 5 maximum.
Also, there was a pullup resistor missing.

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2001\03\06@103611 by Edson Brusque

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Hello Olin,

> There are chips that do this called "high side FET driver".

   do you know who manufactures this chips?

   It sound interesting, but anyway I don't think it could support the
current I want to use (above 5A).

   Thanks

   Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
(47) 323-2685  /  (47) 9993-6453
Blumenau  -  SC  -  Brazil
http://www.citronics.com.br
-----------------------------------

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2001\03\06@150543 by Olin Lathrop

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> > There are chips that do this called "high side FET driver".
>
>     do you know who manufactures this chips?
>
>     It sound interesting, but anyway I don't think it could support the
> current I want to use (above 5A).

The FET driver chip drives the gate of the FET, not the load.  It is up to
you to find a FET rated at 5A.  International Rectifier is one company that
makes FET drivers (and FETs).


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, RemoveMEolinTakeThisOuTspamembedinc.com, http://www.embedinc.com

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2001\03\07@035031 by Alan B. Pearce

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>The FET driver chip drives the gate of the FET, not the load.  It is up to
>you to find a FET rated at 5A.  International Rectifier is one company that
>makes FET drivers (and FETs).

As an aside to this conversation, we have just been advised that the power
devices of Intersil are being taken over by Fairchild. Intersil is another
supplier of high current FET devices.

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