MOSFETs and PWM

no. typical cmos outputs have a diode to vcc so you'll not get the output above with a reasonable pullup resistor and a series diode vcc+1.2V

one easy way to get more voltage use a npn transistor and a pullup resistor, this also inverts the signal so you'll need to adjust the micro's program

.-------------------------------------------------------------. | This is an ascii schematic, if the diagram appears garbled | | try switching to a fixed-pitch font (courier works well) | | pasting it into notepad works well on ms-windows. | | or in google groups "view source" (found under options) | `-------------------------------------------------------------' +v | | | | [1K] ||--+ | ||

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I\'ve used these:

http://www.micrel.com/_PDF/mic4451.pdf

with excellent results on many occasions.

Once even to PWM a motor!

BTW, some work came in and I had to put the pulse counter code on
the back burner, and to top it all off my emulator seems to have
gone south. Aarghhh...

Try John Popelish solution back in 2002 covering this subject. (It'd DejaVu all over again)

+12V---+-----+-----+ | | | 10k | LAMP | |/c | +---|npn | | |\\e | | | |-d +-|

I beieve it, looks like there's enough drive there to turn on about 30 or 40 of my NTEs. ;-)

Was it for an elevator? ;-)

Yeah, yeah, yeah, sure John. (;-)

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Nope, for an orbital welder.

Why use a bipolar to drive a fet? Use a fet to drive a fet!

John

I would feel dirty if I used slip rings. ;-) Ultimately, I'm hoping for an inductive hook-up to transfer the power. I'll need something on the order of 50-100mW max to power the PIC and LEDs, average should be much less especially when simulating analog hands.

Roger on the walking thing, the noise of the air turbulence picks up quickly as you raise the RPMs too. One last little thing, we wouldn't want to impale any innocent bystanders. ;-) I've been using some high brightness LEDs and even using 1K current limiting resistors, they are easily visible with a 1mS pulse. I believe this will give me decent enough looking pixel at ~1000 RPM.

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You could use a rotary transformer, or try this:

news:66r3u25rsmpf7u65hbh7tred1t682scjqf@4ax.com

I find it hard to believe that this little super sot-6 package can handle

6.5Amps, Hell I've blown mosfet in soic-8 packages rated a 4amps. too bad digikey doesn't sell it, I like to try to see where it explodes. ;^D

How about the rotating transformer from a vcr? I don't understand what your doing, but I always thought there should be some use for the nice transformer with good bearings. Probably need to be run at a fairly high frequency. Mike

The obvious, easy way would be to use a small DC motor, mounted in reverse, so that the rotor is attahed to your plinth (or whatever) & your 'blade' is attached to the stator. You'd spin the rotor via a second, conventionally-mounted motor, & power the electronics by rectifying & filtering the AC from the brushes of the spinning motor.

This sounds like a lot of fun. I hope it works out for you!

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   W  "Some people are alive only because it is illegal to kill them."
 . | ,. w ,      
  \\|/  \\|/              Perna condita delenda est
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That was my impression too. We'll see if it lives up to its billing. ;)

I think I haven't made myself clear enough. I'm talking about putting a diode in series with the micro output, with the anode towards it, & the cathode to the MOSFET gate. The pullup resistor would be between the junction of the diode & gate, going to the relay Vcc. The only potential problem I can envisage would be that the logic-low output voltage of the micro would be raised from gnd by the amount of the diode drop. In summary, what I'm suggesting would make the CMOS output of the micro look like an OC TTL output, only raised by a diode drop.

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   W  "Some people are alive only because it is illegal to kill them."
 . | ,. w ,      
  \\|/  \\|/              Perna condita delenda est
---^----^---------------------------------------------------------------

Thanks John. Sorry I didn't get back to you sooner, I had to watch the NASCAR race. :-)

I can't see how the Gate will ever get a signal from the uC that way? with the cathode toward the gate, this would mean that the uC will only be acting as a source and not a sink . Since you have pulled up the Gate input via a R, you need a sink to pull it down. Switching the diode around with the cathode towards the uC will solve that how ever, then you get higher voltage from the Vcc that i assume you may not want in the uC io ? What you need is a simple NPN transistr to be driven from the uC IO used to pull down the pull up Resistor from what ever Vcc source level you need to force the FET on.

Maybe i'm over looking something in your message ?

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"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

D'oh! Yes, you're 100% correct. Dunno what I was thinking there. Thanks for correcting my idiotic mistake in such a tactful manner. :)

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   W  "Some people are alive only because it is illegal to kill them."
 . | ,. w ,      
  \\|/  \\|/              Perna condita delenda est
---^----^---------------------------------------------------------------

That sounds similar to the diagram that John F drew, but his uses a motor with a hollow shaft if I'm interpreting his drawing correctly. If I understand you, you are suggesting the drive motor be offset and use a belt to spin the outside of the other motor (generator).

Thanks, it'll be fun, and I'll learn some new things, no matter what happens. ;-)

I'm not sure what you mean. Are you talking about the head or is there something else?

Never mind, I went and looked it up. Way cool, I never took a VCR that far apart before. I wonder how hard it would be to connect to the read/write head wiring.