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Sci.Electronics.Basics -> MOSFETs and PWM
There are 42 messages in this thread.
You are currently looking at messages 20 to 40.
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Author: John LarkinDate: 00:29 25-02-07
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On Sat, 24 Feb 2007 20:25:50 -0600, "Anthony Fremont"
<spam-not@nowhere.com> wrote:
>John Larkin wrote:
>> On Sat, 24 Feb 2007 19:30:46 -0600, "Anthony Fremont"
>> <spam-not@nowhere.com> wrote:
>>
>>> John Larkin wrote:
>>>> The drain current at "gate threshold" is only 1 mA. The Rdson
at 10
>>>> amps is spec'd with +10 on the gate. So this is of course not a
>>>> logic-level fet, because it wouldn't be prudent to run a beast like
>>>> this with just 3.3 or 5 volts on the gate.
>>>
>>> You are referring to the BUZ11 right?
>>>
>>
>> Yup. The typical curves show it conducting pretty hard, 8 or 9 amps,
>> with +5 on the gate, but that's not guaranteed. If your load is just a
>> couple of amps, it's probably safe to go with +5 drive. But I wouldn't
>> bet a production run on typical performance curves.
>>
>> At 3.3, it might conduct just a few mA, if that.
>
>Just wanted to be sure. The NTE part I mentioned turns on hard at 4V drive.
>They aren't the cheapest things, but so far I like them ok for a jelly-bean
>part. Do you have a favorite cheapie logic-level part in this current
>range?
>
Not up in the amps. I usually whack the big fets with a gate driver,
10 volts maybe.
At lower currents, I use a lot of 2N7002's, pretty good a 5 volts.
They cost about 3 cents each and can switch 50 volts in a couple of
ns.
FDV301 is good at 3.3 volts drive, also fairly low current.
There are tons of logic-level fets around these days. Maybe somebody
else has suggestions.
John
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Author: jasenDate: 02:00 25-02-07
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On 2007-02-25, Lionel <usenet@imagenoir.com> wrote:
> On Sat, 24 Feb 2007 13:03:23 -0600, "Anthony Fremont"
><spam-not@nowhere.com> wrote:
>
> I'm a complete amateur WRT MOSFETs, so I'm finding this discussion
> interesting. I hope you'll bear with me if this question sounds dumb:
>
>>Allot of MOSFETs require high voltages to turn them on (usually you have to
>>pull the gate higher than the highest voltage being switched. For example,
>>if you are using 12V to power the relay, you would have to pull the gate
>>higer than 12V. This can really suck when you want to use a microcontroller
>>to do the switching.
>
> If you're driving the gate from 5V CMOS logis (eg; a micro), can you
> get around this by putting in a series diode after the logic output, &
> a large (1M+) pullup resistor from the MOSFET gate to your 12V (or
> whatever) relay supply?
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] ||--+
| ||<-.
+------||--+
/ |
|/ |
uC +-[1K]--| |
|\| |
~\ |
\ |
| |
--+---------+--- 0V
Bye.
Jasen
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Author: John FieldsDate: 08:26 25-02-07
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On Sat, 24 Feb 2007 16:10:44 -0600, "Anthony Fremont"
<spam-not@nowhere.com> wrote:
>John Fields wrote:
>> On Sat, 24 Feb 2007 14:43:42 -0600, "Anthony Fremont"
>> <spam-not@nowhere.com> wrote:
>>
>>> maxfoo@punkass.com wrote:
>>>
>>>> Don't think that's correct Anthony.
>>>> Typically the gate threshold for a 30A MOSFET is 2-4 volts. For
>>>> example take a look at a BUZ11
>>>> http://www.fairchildsemi.com/ds/BU/BUZ11.pdf, maybe you're defining
>>>> this as a logic level fet too. ;)
>>>
>>> Vgs(th) for the NTE part is 2V max. .05 Ohms Rds(on) is at 5V gate
>>> drive. At 4V drive, the on resistance is .07 Ohms max. Sounds like
>>> logic-level to me. ;-)
>>
>> ---
>> Regardless, you'll need to know how long it takes to charge up the
>> gate capacitance between when the switch is "ON" and how long it'll
>> take to discharge it when it's "OFF", since during that time the FET
>> will be required to dissipate extraordinary power.
>
>If I was actually going to try and switch 30A with it, I guess I'd use a
>gate-driver of some type. I have some in my shack that are made by
>Microchip (IIRC) that I used for tinkering with some IGBTs. They have very
>fast switching times and will supply much larger currents (>3A) during the
>transition. The NTE transistors that I mentioned seem to work fine being
>driven by a PIC at 5V. I was only switching a couple of amps though without
>a heatsink.
---
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...
--
JF
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On Feb 25, 2:00 am, jasen <j...@free.net.nz> wrote:
> On 2007-02-25, Lionel <use...@imagenoir.com> wrote:
>
>
>
>
>
> > On Sat, 24 Feb 2007 13:03:23 -0600, "Anthony Fremont"
> ><spam-...@nowhere.com> wrote:
>
> > I'm a complete amateur WRT MOSFETs, so I'm finding this discussion
> > interesting. I hope you'll bear with me if this question sounds dumb:
>
> >>Allot of MOSFETs require high voltages to turn them on (usually you have to
> >>pull the gate higher than the highest voltage being switched. For example,
> >>if you are using 12V to power the relay, you would have to pull the gate
> >>higer than 12V. This can really suck when you want to use a
microcontroller
> >>to do the switching.
>
> > If you're driving the gate from 5V CMOS logis (eg; a micro), can you
> > get around this by putting in a series diode after the logic output, &
> > a large (1M+) pullup resistor from the MOSFET gate to your 12V (or
> > whatever) relay supply?
>
> 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] ||--+
> | ||<-.
> +------||--+
> / |
> |/ |
> uC +-[1K]--| |
> |\| |
> ~\ |
> \ |
> | |
> --+---------+--- 0V
>
> Bye.
> Jasen-
Try John Popelish solution back in 2002 covering this subject.
(It'd DejaVu all over again)
+12V---+-----+-----+
| | |
10k | LAMP
| |/c |
+---|npn |
| |\e |
| | |-d
+-|<--+----| Nfet
|/ c |-s
logic-|npn |
|\e |
com----+-----------+
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Author: Anthony FremontDate: 09:50 25-02-07
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John Fields wrote:
> On Sat, 24 Feb 2007 16:10:44 -0600, "Anthony Fremont"
>> If I was actually going to try and switch 30A with it, I guess I'd
>> use a gate-driver of some type. I have some in my shack that are
>> made by Microchip (IIRC) that I used for tinkering with some IGBTs.
>> They have very fast switching times and will supply much larger
>> currents (>3A) during the transition. The NTE transistors that I
>> mentioned seem to work fine being driven by a PIC at 5V. I was only
>> switching a couple of amps though without a heatsink.
>
> ---
> I've used these:
>
> http://www.micrel.com/_PDF/mic4451.pdf
>
> with excellent results on many occasions.
I beieve it, looks like there's enough drive there to turn on about 30 or 40
of my NTEs. ;-)
> Once even to PWM a motor!
Was it for an elevator? ;-)
> 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...
Yeah, yeah, yeah, sure John. (;-) <---- It's a joke! It's a joke!
I know how it goes.
I've been tinkering with my propellor clock ideas again. Most of the
electronic problems are easy enough to solve, it's the mechanical ones that
keep getting in the way.
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Author: John FieldsDate: 12:37 25-02-07
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On Sun, 25 Feb 2007 08:50:33 -0600, "Anthony Fremont"
<spam-not@nowhere.com> wrote:
>John Fields wrote:
>> On Sat, 24 Feb 2007 16:10:44 -0600, "Anthony Fremont"
>
>
>>> If I was actually going to try and switch 30A with it, I guess I'd
>>> use a gate-driver of some type. I have some in my shack that are
>>> made by Microchip (IIRC) that I used for tinkering with some IGBTs.
>>> They have very fast switching times and will supply much larger
>>> currents (>3A) during the transition. The NTE transistors that I
>>> mentioned seem to work fine being driven by a PIC at 5V. I was only
>>> switching a couple of amps though without a heatsink.
>>
>> ---
>> I've used these:
>>
>> http://www.micrel.com/_PDF/mic4451.pdf
>>
>> with excellent results on many occasions.
>
>I beieve it, looks like there's enough drive there to turn on about 30 or 40
>of my NTEs. ;-)
>
>> Once even to PWM a motor!
>
>Was it for an elevator? ;-)
---
Nope, for an orbital welder.
---
>> 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...
>
>Yeah, yeah, yeah, sure John. (;-) <---- It's a joke! It's a joke!
>I know how it goes.
>
>I've been tinkering with my propellor clock ideas again. Most of the
>electronic problems are easy enough to solve, it's the mechanical ones that
>keep getting in the way.
---
Like slip rings and getting things balanced so they don't walk
across the room by themselves?
--
JF
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Author: John LarkinDate: 13:10 25-02-07
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On 25 Feb 2007 07:00:48 GMT, jasen <jasen@free.net.nz> wrote:
>On 2007-02-25, Lionel <usenet@imagenoir.com> wrote:
>> On Sat, 24 Feb 2007 13:03:23 -0600, "Anthony Fremont"
>><spam-not@nowhere.com> wrote:
>>
>> I'm a complete amateur WRT MOSFETs, so I'm finding this discussion
>> interesting. I hope you'll bear with me if this question sounds dumb:
>>
>>>Allot of MOSFETs require high voltages to turn them on (usually you have to
>>>pull the gate higher than the highest voltage being switched. For example,
>>>if you are using 12V to power the relay, you would have to pull the gate
>>>higer than 12V. This can really suck when you want to use a microcontroller
>>>to do the switching.
>>
>> If you're driving the gate from 5V CMOS logis (eg; a micro), can you
>> get around this by putting in a series diode after the logic output, &
>> a large (1M+) pullup resistor from the MOSFET gate to your 12V (or
>> whatever) relay supply?
>
>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] ||--+
> | ||<-.
> +------||--+
> / |
> |/ |
> uC +-[1K]--| |
> |\| |
> ~\ |
> \ |
> | |
> --+---------+--- 0V
>
>
>Bye.
> Jasen
Why use a bipolar to drive a fet? Use a fet to drive a fet!
> +v
> | |
> | |
> [1K] ||--+
> | ||<-.
> +------||--+
> | |
> | | |
> uC --------| |
> | > |
> | |
> | |
> | |
> --+-----------+--- 0V
John
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Author: Anthony FremontDate: 13:32 25-02-07
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John Fields wrote:
> On Sun, 25 Feb 2007 08:50:33 -0600, "Anthony Fremont"
>> I've been tinkering with my propellor clock ideas again. Most of the
>> electronic problems are easy enough to solve, it's the mechanical
>> ones that keep getting in the way.
>
> ---
> Like slip rings and getting things balanced so they don't walk
> across the room by themselves?
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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Author: John FieldsDate: 15:16 25-02-07
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On Sun, 25 Feb 2007 12:32:45 -0600, "Anthony Fremont"
<spam-not@nowhere.com> wrote:
>John Fields wrote:
>> On Sun, 25 Feb 2007 08:50:33 -0600, "Anthony Fremont"
>
>>> I've been tinkering with my propellor clock ideas again. Most of the
>>> electronic problems are easy enough to solve, it's the mechanical
>>> ones that keep getting in the way.
>>
>> ---
>> Like slip rings and getting things balanced so they don't walk
>> across the room by themselves?
>
>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.
---
You could use a rotary transformer, or try this:
news:66r3u25rsmpf7u65hbh7tred1t682scjqf@4ax.com
--
JF
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Author: maxfooDate: 15:23 25-02-07
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On Sat, 24 Feb 2007 22:28:18 GMT, Randy Day <randy.day@shaw.cax> wrote:
>John Larkin wrote:
>
>[snip]
>The FDC655 lists 33 mOhms Rds(on) at 4.5v, which
>seems more than adequate. I think I'll go with it.
>
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
http://www.fairchildsemi.com/ds/FD/FDC655BN.pdf
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Author: amdxDate: 17:08 25-02-07
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"Anthony Fremont" <spam-not@nowhere.com> wrote in message
news:12u3lig7ir1pg28@news.supernews.com...
> John Fields wrote:
>> On Sun, 25 Feb 2007 08:50:33 -0600, "Anthony Fremont"
>
>>> I've been tinkering with my propellor clock ideas again. Most of the
>>> electronic problems are easy enough to solve, it's the mechanical
>>> ones that keep getting in the way.
>>
>> ---
>> Like slip rings and getting things balanced so they don't walk
>> across the room by themselves?
>
> 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.
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
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Author: LionelDate: 19:13 25-02-07
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On Sun, 25 Feb 2007 12:32:45 -0600, "Anthony Fremont"
<spam-not@nowhere.com> wrote:
>John Fields wrote:
>> On Sun, 25 Feb 2007 08:50:33 -0600, "Anthony Fremont"
>
>>> I've been tinkering with my propellor clock ideas again. Most of the
>>> electronic problems are easy enough to solve, it's the mechanical
>>> ones that keep getting in the way.
>>
>> ---
>> Like slip rings and getting things balanced so they don't walk
>> across the room by themselves?
>
>I would feel dirty if I used slip rings. ;-) Ultimately, I'm hoping for an
>inductive hook-up to transfer the power.
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.
> 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.
This sounds like a lot of fun. I hope it works out for you!
--
W "Some people are alive only because it is illegal to kill them."
. | ,. w ,
\|/ \|/ Perna condita delenda est
---^----^---------------------------------------------------------------
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Author: Randy DayDate: 19:34 25-02-07
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maxfoo wrote:
> On Sat, 24 Feb 2007 22:28:18 GMT, Randy Day <randy.day@shaw.cax> wrote:
>
>
>>John Larkin wrote:
>>
>>[snip]
>
>
>>The FDC655 lists 33 mOhms Rds(on) at 4.5v, which
>>seems more than adequate. I think I'll go with it.
>>
>
>
> 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
> http://www.fairchildsemi.com/ds/FD/FDC655BN.pdf
That was my impression too. We'll see if it lives
up to its billing. ;)
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Author: LionelDate: 20:28 25-02-07
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On 25 Feb 2007 07:00:48 GMT, jasen <jasen@free.net.nz> wrote:
>On 2007-02-25, Lionel <usenet@imagenoir.com> wrote:
>> On Sat, 24 Feb 2007 13:03:23 -0600, "Anthony Fremont"
>><spam-not@nowhere.com> wrote:
>>
>> I'm a complete amateur WRT MOSFETs, so I'm finding this discussion
>> interesting. I hope you'll bear with me if this question sounds dumb:
>>
>>>Allot of MOSFETs require high voltages to turn them on (usually you have to
>>>pull the gate higher than the highest voltage being switched. For example,
>>>if you are using 12V to power the relay, you would have to pull the gate
>>>higer than 12V. This can really suck when you want to use a microcontroller
>>>to do the switching.
>>
>> If you're driving the gate from 5V CMOS logis (eg; a micro), can you
>> get around this by putting in a series diode after the logic output, &
>> a large (1M+) pullup resistor from the MOSFET gate to your 12V (or
>> whatever) relay supply?
>
>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
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.
--
W "Some people are alive only because it is illegal to kill them."
. | ,. w ,
\|/ \|/ Perna condita delenda est
---^----^---------------------------------------------------------------
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Author: Anthony FremontDate: 20:39 25-02-07
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John Fields wrote:
> On Sun, 25 Feb 2007 12:32:45 -0600, "Anthony Fremont"
> <spam-not@nowhere.com> wrote:
>
>> John Fields wrote:
>>> On Sun, 25 Feb 2007 08:50:33 -0600, "Anthony Fremont"
>>
>>>> I've been tinkering with my propellor clock ideas again. Most of
>>>> the electronic problems are easy enough to solve, it's the
>>>> mechanical ones that keep getting in the way.
>>>
>>> ---
>>> Like slip rings and getting things balanced so they don't walk
>>> across the room by themselves?
>>
>> 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.
>
> ---
> You could use a rotary transformer, or try this:
>
> news:66r3u25rsmpf7u65hbh7tred1t682scjqf@4ax.com
Thanks John. Sorry I didn't get back to you sooner, I had to watch the
NASCAR race. :-)
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Author: JamieDate: 21:05 25-02-07
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Lionel wrote:
> On 25 Feb 2007 07:00:48 GMT, jasen <jasen@free.net.nz> wrote:
>
>
>>On 2007-02-25, Lionel <usenet@imagenoir.com> wrote:
>>
>>>On Sat, 24 Feb 2007 13:03:23 -0600, "Anthony Fremont"
>>><spam-not@nowhere.com> wrote:
>>>
>>>I'm a complete amateur WRT MOSFETs, so I'm finding this discussion
>>>interesting. I hope you'll bear with me if this question sounds dumb:
>>>
>>>
>>>>Allot of MOSFETs require high voltages to turn them on (usually you have
to
>>>>pull the gate higher than the highest voltage being switched. For
example,
>>>>if you are using 12V to power the relay, you would have to pull the gate
>>>>higer than 12V. This can really suck when you want to use a
microcontroller
>>>>to do the switching.
>>>
>>>If you're driving the gate from 5V CMOS logis (eg; a micro), can you
>>>get around this by putting in a series diode after the logic output, &
>>>a large (1M+) pullup resistor from the MOSFET gate to your 12V (or
>>>whatever) relay supply?
>>
>>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
>
>
> 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.
>
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 ?
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
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Author: LionelDate: 21:11 25-02-07
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On Sun, 25 Feb 2007 21:05:25 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:
>Lionel wrote:
>> 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.
>>
>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 .
<slaps self> D'oh! Yes, you're 100% correct.
Dunno what I was thinking there. Thanks for correcting my idiotic
mistake in such a tactful manner. :)
--
W "Some people are alive only because it is illegal to kill them."
. | ,. w ,
\|/ \|/ Perna condita delenda est
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Author: Anthony FremontDate: 19:02 26-02-07
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Lionel wrote:
> On Sun, 25 Feb 2007 12:32:45 -0600, "Anthony Fremont"
> <spam-not@nowhere.com> wrote:
>
>> John Fields wrote:
>>> On Sun, 25 Feb 2007 08:50:33 -0600, "Anthony Fremont"
>>
>>>> I've been tinkering with my propellor clock ideas again. Most of
>>>> the electronic problems are easy enough to solve, it's the
>>>> mechanical ones that keep getting in the way.
>>>
>>> ---
>>> Like slip rings and getting things balanced so they don't walk
>>> across the room by themselves?
>>
>> I would feel dirty if I used slip rings. ;-) Ultimately, I'm
>> hoping for an inductive hook-up to transfer the power.
>
> 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.
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).
>> 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.
>
> This sounds like a lot of fun. I hope it works out for you!
Thanks, it'll be fun, and I'll learn some new things, no matter what
happens. ;-)
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Author: Anthony FremontDate: 19:03 26-02-07
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amdx wrote:
> 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
I'm not sure what you mean. Are you talking about the head or is there
something else?
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Author: Anthony FremontDate: 19:10 26-02-07
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Anthony Fremont wrote:
> amdx wrote:
>
>> 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
>
> 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.
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Contact | Electronic Portal
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