DPRG
DPRG List  



DPRG: Re:

Subject: DPRG: Re:
From: Larry Kerns l.kerns at worldnet.att.net
Date: Tue Nov 23 10:16:28 CST 1999

I might also add that the N-channel MOSFETs have a MUCH lower "on" resistance
than a comparable P-channel device thus causing the P-channel device to dissipate
MUCH more power and thus heat.  To buy a comparable P-channel device with lower
"on" resistance is what costs all of the money.

Larry Kerns
==================================================

Jim Brown wrote:

> At 11:24 AM 11/19/99 -0000, you wrote:
> >   DEAR SIR,                A THIRD YEAR STUDENT AT EAST LONDON
> >UNIVERSITY,CURRENTLY RESERCHING  CLASS D AUDIO AMPS.I WOULD BE GRATEFULL IF
> >YOU COULD ENLIGHTEN ME ON THE  FOLLOWING: 1.WHAT IS THE RATIONALE BEHIND
> >N-CHANNEL ONLY  H-BRIDGES,AND COMPLEMENTARY H-BRIDGES/ 2.WHAT DRIVE
> >CIRCUTERY WOULD YOU RECOMMEND BETWEEN  MODULATOR,(GENERATING PWM PULSE),AND
> >H-BRIDGE? I LOOK FOWARD TO HEARING FROM YOU.
> >MIKE
>
> N-Channel mosfets are very cheap like $0.39 cents, while P-Channel mosfets
> are very expensive like a few dollars.  If you can use all N-Channel mosfets
> you might save yourself some cash especially if you plan on making a bunch of
> them.  The way it works is to overcome the breakdown voltage of the N-Channel
> gate by doubling the voltage (ok, more like 7v or 10v higher).  If you
> already have the higher voltage supplied, it might make sense to go with all
> N-Channels on your h-bridge, but if you have to add a voltage doubling
> circuit, then you might as well just buy P-Channel mosfets.  The pulse
> generating circuit could be done a number of ways.  Egads, you could use
> a 555 timer (but don't tell anyone I recommended that), or if you're already
> hooked to a microcontroller, have software spit out a PWM signal (my
> prefrence), or you could use some sort of pwm timing chip, some people
> even just use a EPROM programmed with about 16 different pulse widths and
> send them to the h-bridge.  However, unless you just need the kind of
> amperage a mosfet can supply (like 50amps) and if you really only need
> at most 2-3 amps go with a canned h-bridge circuit like the L298 or
> the LMD18200.  These can drive motors up to about the size of a coke can
> which fits most needs.  It's much easier and cheaper than designing your
> own circuit.
>
> Here's some web pages I hope will help:
>         http://www.dprg.org/hbridge.html
>         http://www.dprg.org/l298.html
>         http://www.dprg.org/hbridge_theory.html
>
> - - ____ - - - - - - ___ - - - - - - - - - - - - - - - - - - - - - - - - - -
>     \/\_\@  ____    /  /\ __  ___          ___    http://www.dprg.org
>     / / /\ / / /\  /--/ //\_\/\_/\ /\/\/\ /\_/\  brownjim at airmail.net
> /__/ / / // / / / /__/ // / /__/ //_/_/ // // /  (972)495-3821
> \__\/  \/ \/\/\/  \__\/ \/  \__\/ \_\_\/ \/ \/ james_121 at yahoo.com
> jim_brown at bigfoot.com jbrown at dprg.org http://www.cyberramp.net/~jbrown
> Cole's Law:  Thinly Shreaded Cabbage

------------------------------


More information about the DPRG mailing list