mosfet driver needed for logic-level mosfets?

On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote:

On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote:

Hello,

I've discovered logic-level mosfets, and am using an Arduino to drive a
small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N
as the power mosfet.

Would a mosfet-driver be recommended to switch that mosfet on and off
more quickly? Or is a logic-level mosfet already designed to
efficiently turn on and off with the weak logic level signal?

Given that you are also asking about BJT vs. FET, note that in order to
switch at it's fastest, a BJT needs a base driver that can push charge in
quickly and actively pull it out quickly. The difference in recovery
from saturation when you pull the base below ground vs. when you just
pull it _to_ ground can be dramatic.

And don't use a grotty old TIP31 if you want speed -- Zetex developed
some pretty impressive modern BJTs before they got bought by Diodes,
Inc., and turned into a cash cow. Those transistors are still sold, and
have some pretty impressive HFE_sat and VCE_sat numbers.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

This is an interesting article. It does mention pulling the base to -1V. Is this the article you were referring to?

https://www.diodes.com/assets/App-Note-Files/zetex/an14.pdf

Also noteworthy:

"This isn't to exclude MOSFET based designs (some IC vendors have specified MOS as this suits their technology) but in terms of equivalent on-resistance and silicon efficiency, the low voltage bipolar device has no equal. For example, the ZETEX ZTX849 E-Line (TO-92 compatible) transistor exhibits a RCE(sat) of 36mΩ. This can only be matched by a much larger (and expensive) MOSFET die, only
available in TO-220, D-Pak, and similar larger packages."

Michael

 

[Tim Wescott]

On Tue, 16 May 2017 11:56:55 -0700, mrdarrett wrote:

On Tuesday, May 16, 2017 at 11:01:05 AM UTC-7, Tim Wescott wrote:

~kapow~


Ok, thanks for the information. You've given me lots to think
about.

For higher-speed switching of BJTs, you recommend yanking the base
to *below* ground, then?

Yes. But not too far... ~3V maximum to avoid VBE breakdown.


Oh cool. Thanks.

Michael

circuit is something called the Baker clamp

https://en.wikipedia.org/wiki/Baker_clamp

That's not at all what I was referring to. Zetex (or somebody) figured
out that you could go ahead and let the transistor saturate, but still
get significantly faster turn-off if you actively drew the carriers out
of the base.

--

Tim Wescott Wescott Design Services http://www.wescottdesign.com

I'm looking for work -- see my website!


Is the app note somewhere in here? It's not exactly organized by Zetex,
but maybe you remember parts of the name of the app note..?

https://www.diodes.com/design/support/application-notes/

It's too bad that companies don't always keep the old website when they
get bought out...

Michael

Not there, but here:
http://www.euedia.tuiasi.ro/lab_ep/ep_files/Lab_no_4_c1.pdf

and here:
http://nptel.ac.in/courses/108105066/PDF/L-3(DK)(PE)%20((EE)NPTEL).pdf

and here:
<https://electronics.stackexchange.com/questions/23349/how-do-i-make-the-
turn-off-and-turn-on-time-equal-in-a-npn-transistor>

which references this excerpt from a book:
http://wps.prenhall.com/chet_paynter_introduct_6/0,5779,426359-,00.html

This all came by searching on "speed up bjt switching with negative base
drive" -- there are probably other fortuitous combinations if you wish to
exercise your Google-Fu.

--
www.wescottdesign.com

 

[Tim Wescott]

On Tue, 16 May 2017 12:42:58 -0700, mrdarrett wrote:

On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote:
On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote:

Hello,

I've discovered logic-level mosfets, and am using an Arduino to drive
a small 12VDC (about an amp or so) pump motor with PWM, using an
IRLZ34N as the power mosfet.

Would a mosfet-driver be recommended to switch that mosfet on and off
more quickly? Or is a logic-level mosfet already designed to
efficiently turn on and off with the weak logic level signal?

Given that you are also asking about BJT vs. FET, note that in order to
switch at it's fastest, a BJT needs a base driver that can push charge
in quickly and actively pull it out quickly. The difference in
recovery from saturation when you pull the base below ground vs. when
you just pull it _to_ ground can be dramatic.

And don't use a grotty old TIP31 if you want speed -- Zetex developed
some pretty impressive modern BJTs before they got bought by Diodes,
Inc., and turned into a cash cow. Those transistors are still sold,
and have some pretty impressive HFE_sat and VCE_sat numbers.

--

Tim Wescott Wescott Design Services http://www.wescottdesign.com

I'm looking for work -- see my website!


This is an interesting article. It does mention pulling the base to
-1V. Is this the article you were referring to?

https://www.diodes.com/assets/App-Note-Files/zetex/an14.pdf

Also noteworthy:

"This isn't to exclude MOSFET based designs (some IC vendors have
specified MOS as this suits their technology) but in terms of equivalent
on-resistance and silicon efficiency, the low voltage bipolar device has
no equal. For example, the ZETEX ZTX849 E-Line (TO-92 compatible)
transistor exhibits a RCE(sat) of 36mΩ. This can only be matched by a
much larger (and expensive) MOSFET die, only available in TO-220, D-Pak,
and similar larger packages."

Michael

I think there was more than that, but dangit, I can't remember.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[default]

On Tue, 16 May 2017 13:00:57 -0500, Tim Wescott
<seemywebsite@myfooter.really> wrote:

On Tue, 16 May 2017 05:01:34 -0400, default wrote:

On Mon, 15 May 2017 12:02:39 -0700 (PDT), mrdarrett@gmail.com wrote:

On Monday, May 15, 2017 at 11:58:39 AM UTC-7, Jim Thompson wrote:
On Mon, 15 May 2017 11:33:07 -0700 (PDT), mrdarrett@gmail.com wrote:

On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote:
On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote:

Hello,

I've discovered logic-level mosfets, and am using an Arduino to
drive a small 12VDC (about an amp or so) pump motor with PWM,
using an IRLZ34N as the power mosfet.

Would a mosfet-driver be recommended to switch that mosfet on and
off more quickly? Or is a logic-level mosfet already designed to
efficiently turn on and off with the weak logic level signal?

Given that you are also asking about BJT vs. FET, note that in
order to switch at it's fastest, a BJT needs a base driver that can
push charge in quickly and actively pull it out quickly. The
difference in recovery from saturation when you pull the base below
ground vs. when you just pull it _to_ ground can be dramatic.

And don't use a grotty old TIP31 if you want speed -- Zetex
developed some pretty impressive modern BJTs before they got bought
by Diodes, Inc., and turned into a cash cow. Those transistors are
still sold, and have some pretty impressive HFE_sat and VCE_sat
numbers.

--

Tim Wescott Wescott Design Services http://www.wescottdesign.com

I'm looking for work -- see my website!


Ok, thanks for the information. You've given me lots to think about.

For higher-speed switching of BJTs, you recommend yanking the base to
*below* ground, then?

Yes. But not too far... ~3V maximum to avoid VBE breakdown.


Oh cool. Thanks.

Michael

circuit is something called the Baker clamp

https://en.wikipedia.org/wiki/Baker_clamp

That's not at all what I was referring to. Zetex (or somebody) figured
out that you could go ahead and let the transistor saturate, but still
get significantly faster turn-off if you actively drew the carriers out
of the base.

Fred Baker was doing that. We had these plasma panels that had a
complex waveform and had to refresh the things at 15KHZ horizontal
rate just like NTSC TV (back in the 70's) ~1/2 million pixals... X-Y
diode steered addressing lines, I forget how fast the transistors were
working but it was way beyond anything that this guy's PWM might
encounter.

One beauty of the panels (that we took advantage of) was that it
didn't require memory, light up a pixal on the screen and it stayed
there until you changed it, due to some magic in the power supply -
some kind of stepped waveform. My memory isn't up to describing the
whole system...

 

[rickman]

On 5/16/2017 12:46 PM, Jim Thompson wrote:

On Tue, 16 May 2017 09:31:14 -0700 (PDT), mrdarrett@gmail.com wrote:

On Tuesday, May 16, 2017 at 2:01:36 AM UTC-7, default wrote:
On Mon, 15 May 2017 12:02:39 -0700 (PDT), mrdarrett@gmail.com wrote:

On Monday, May 15, 2017 at 11:58:39 AM UTC-7, Jim Thompson wrote:
On Mon, 15 May 2017 11:33:07 -0700 (PDT), mrdarrett@gmail.com wrote:

On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote:
On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote:

Hello,

I've discovered logic-level mosfets, and am using an Arduino to drive a
small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N
as the power mosfet.

Would a mosfet-driver be recommended to switch that mosfet on and off
more quickly? Or is a logic-level mosfet already designed to
efficiently turn on and off with the weak logic level signal?

Given that you are also asking about BJT vs. FET, note that in order to
switch at it's fastest, a BJT needs a base driver that can push charge in
quickly and actively pull it out quickly. The difference in recovery
from saturation when you pull the base below ground vs. when you just
pull it _to_ ground can be dramatic.

And don't use a grotty old TIP31 if you want speed -- Zetex developed
some pretty impressive modern BJTs before they got bought by Diodes,
Inc., and turned into a cash cow. Those transistors are still sold, and
have some pretty impressive HFE_sat and VCE_sat numbers.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!


Ok, thanks for the information. You've given me lots to think about.

For higher-speed switching of BJTs, you recommend yanking the base to *below* ground, then?

Yes. But not too far... ~3V maximum to avoid VBE breakdown.


Oh cool. Thanks.

Michael

circuit is something called the Baker clamp

https://en.wikipedia.org/wiki/Baker_clamp


Impressive! Thanks!

But by avoiding saturation, Vce,sat is not minimized, is it..?

Michael

A Baker clamp minimizes recovery time by preventing hard saturation
and charge storage... "Vsat" is now typically equal to Vbe.

But, as shown by "default", it also prevents quickly sucking charge
out of the base... more complex arrangements are required.

Or something simpler. Isn't that what the Schottky transistor does? It
uses a single Schottky diode between the base and collector. Since the
Schottky diode forward voltage is lower than the Vbe voltage it limits
the collector voltage and keeps it out of saturation. But now there is
no diode blocking the current path to turn off the base and drain the
charge.

--

Rick C

 

[rickman]

On 5/16/2017 2:00 PM, Tim Wescott wrote:

On Tue, 16 May 2017 05:01:34 -0400, default wrote:

On Mon, 15 May 2017 12:02:39 -0700 (PDT), mrdarrett@gmail.com wrote:

On Monday, May 15, 2017 at 11:58:39 AM UTC-7, Jim Thompson wrote:
On Mon, 15 May 2017 11:33:07 -0700 (PDT), mrdarrett@gmail.com wrote:

On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote:
On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote:

Hello,

I've discovered logic-level mosfets, and am using an Arduino to
drive a small 12VDC (about an amp or so) pump motor with PWM,
using an IRLZ34N as the power mosfet.

Would a mosfet-driver be recommended to switch that mosfet on and
off more quickly? Or is a logic-level mosfet already designed to
efficiently turn on and off with the weak logic level signal?

Given that you are also asking about BJT vs. FET, note that in
order to switch at it's fastest, a BJT needs a base driver that can
push charge in quickly and actively pull it out quickly. The
difference in recovery from saturation when you pull the base below
ground vs. when you just pull it _to_ ground can be dramatic.

And don't use a grotty old TIP31 if you want speed -- Zetex
developed some pretty impressive modern BJTs before they got bought
by Diodes, Inc., and turned into a cash cow. Those transistors are
still sold, and have some pretty impressive HFE_sat and VCE_sat
numbers.

--

Tim Wescott Wescott Design Services http://www.wescottdesign.com

I'm looking for work -- see my website!


Ok, thanks for the information. You've given me lots to think about.

For higher-speed switching of BJTs, you recommend yanking the base to
*below* ground, then?

Yes. But not too far... ~3V maximum to avoid VBE breakdown.


Oh cool. Thanks.

Michael

circuit is something called the Baker clamp

https://en.wikipedia.org/wiki/Baker_clamp

That's not at all what I was referring to. Zetex (or somebody) figured
out that you could go ahead and let the transistor saturate, but still
get significantly faster turn-off if you actively drew the carriers out
of the base.

That sounds similar to what they did in WWII radar sets where they drove
the grid positive with respect to the cathode to drive more current to
the plate. The grid would conduct significant current, but since they
were generating pulses with a relatively low duty cycle the grid didn't
melt.

--

Rick C

 

[Tim Wescott]

On Tue, 16 May 2017 21:27:43 -0400, rickman wrote:

On 5/16/2017 2:00 PM, Tim Wescott wrote:
On Tue, 16 May 2017 05:01:34 -0400, default wrote:

On Mon, 15 May 2017 12:02:39 -0700 (PDT), mrdarrett@gmail.com wrote:

On Monday, May 15, 2017 at 11:58:39 AM UTC-7, Jim Thompson wrote:
On Mon, 15 May 2017 11:33:07 -0700 (PDT), mrdarrett@gmail.com wrote:

On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote:
On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote:

Hello,

I've discovered logic-level mosfets, and am using an Arduino to
drive a small 12VDC (about an amp or so) pump motor with PWM,
using an IRLZ34N as the power mosfet.

Would a mosfet-driver be recommended to switch that mosfet on and
off more quickly? Or is a logic-level mosfet already designed to
efficiently turn on and off with the weak logic level signal?

Given that you are also asking about BJT vs. FET, note that in
order to switch at it's fastest, a BJT needs a base driver that
can push charge in quickly and actively pull it out quickly. The
difference in recovery from saturation when you pull the base
below ground vs. when you just pull it _to_ ground can be
dramatic.

And don't use a grotty old TIP31 if you want speed -- Zetex
developed some pretty impressive modern BJTs before they got
bought by Diodes, Inc., and turned into a cash cow. Those
transistors are still sold, and have some pretty impressive
HFE_sat and VCE_sat numbers.

--

Tim Wescott Wescott Design Services http://www.wescottdesign.com

I'm looking for work -- see my website!


Ok, thanks for the information. You've given me lots to think
about.

For higher-speed switching of BJTs, you recommend yanking the base
to *below* ground, then?

Yes. But not too far... ~3V maximum to avoid VBE breakdown.


Oh cool. Thanks.

Michael

circuit is something called the Baker clamp

https://en.wikipedia.org/wiki/Baker_clamp

That's not at all what I was referring to. Zetex (or somebody) figured
out that you could go ahead and let the transistor saturate, but still
get significantly faster turn-off if you actively drew the carriers out
of the base.

That sounds similar to what they did in WWII radar sets where they drove
the grid positive with respect to the cathode to drive more current to
the plate. The grid would conduct significant current, but since they
were generating pulses with a relatively low duty cycle the grid didn't
melt.

There are class-B amplifier tubes that are designed for that even with
continuous-wave or audio service -- but they need to have grids that are
capable of withstanding (and dissipating, I think) the extra heat.

--
www.wescottdesign.com

 

[John Larkin]

On Tue, 16 May 2017 12:42:58 -0700 (PDT), mrdarrett@gmail.com wrote:

On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote:
On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote:

Hello,

I've discovered logic-level mosfets, and am using an Arduino to drive a
small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N
as the power mosfet.

Would a mosfet-driver be recommended to switch that mosfet on and off
more quickly? Or is a logic-level mosfet already designed to
efficiently turn on and off with the weak logic level signal?

Given that you are also asking about BJT vs. FET, note that in order to
switch at it's fastest, a BJT needs a base driver that can push charge in
quickly and actively pull it out quickly. The difference in recovery
from saturation when you pull the base below ground vs. when you just
pull it _to_ ground can be dramatic.

And don't use a grotty old TIP31 if you want speed -- Zetex developed
some pretty impressive modern BJTs before they got bought by Diodes,
Inc., and turned into a cash cow. Those transistors are still sold, and
have some pretty impressive HFE_sat and VCE_sat numbers.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!


This is an interesting article. It does mention pulling the base to -1V. Is this the article you were referring to?

https://www.diodes.com/assets/App-Note-Files/zetex/an14.pdf

Also noteworthy:

"This isn't to exclude MOSFET based designs (some IC vendors have specified MOS as this suits their technology) but in terms of equivalent on-resistance and silicon efficiency, the low voltage bipolar device has no equal. For example, the ZETEX ZTX849 E-Line (TO-92 compatible) transistor exhibits a RCE(sat) of 36m?. This can only be matched by a much larger (and expensive) MOSFET die, only
available in TO-220, D-Pak, and similar larger packages."

Michael

That's kinda old. Actually, very old. There are some milliohm mosfets
around now.

https://www.digikey.com/product-detail/en/alpha-omega-semiconductor-inc/AO3416/785-1011-2-ND/1855783



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

On Tuesday, May 16, 2017 at 8:30:26 PM UTC-7, John Larkin wrote:

On Tue, 16 May 2017 12:42:58 -0700 (PDT), mrdarrett@gmail.com wrote:

On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote:
On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote:

Hello,

I've discovered logic-level mosfets, and am using an Arduino to drive a
small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N
as the power mosfet.

Would a mosfet-driver be recommended to switch that mosfet on and off
more quickly? Or is a logic-level mosfet already designed to
efficiently turn on and off with the weak logic level signal?

Given that you are also asking about BJT vs. FET, note that in order to
switch at it's fastest, a BJT needs a base driver that can push charge in
quickly and actively pull it out quickly. The difference in recovery
from saturation when you pull the base below ground vs. when you just
pull it _to_ ground can be dramatic.

And don't use a grotty old TIP31 if you want speed -- Zetex developed
some pretty impressive modern BJTs before they got bought by Diodes,
Inc., and turned into a cash cow. Those transistors are still sold, and
have some pretty impressive HFE_sat and VCE_sat numbers.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!


This is an interesting article. It does mention pulling the base to -1V.. Is this the article you were referring to?

https://www.diodes.com/assets/App-Note-Files/zetex/an14.pdf

Also noteworthy:

"This isn't to exclude MOSFET based designs (some IC vendors have specified MOS as this suits their technology) but in terms of equivalent on-resistance and silicon efficiency, the low voltage bipolar device has no equal. For example, the ZETEX ZTX849 E-Line (TO-92 compatible) transistor exhibits a RCE(sat) of 36m?. This can only be matched by a much larger (and expensive) MOSFET die, only
available in TO-220, D-Pak, and similar larger packages."

Michael

That's kinda old. Actually, very old. There are some milliohm mosfets
around now.

https://www.digikey.com/product-detail/en/alpha-omega-semiconductor-inc/AO3416/785-1011-2-ND/1855783



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

Oh nice!

From the datasheet, Vgs,th,max = 1.1V. This should work fine as a logic-level mosfet, then?

http://aosmd.com/res/data_sheets/AO3416.pdf

In general, for PWM at 1-2A, 12-18VDC, are mosfets preferred (lower resistance, cheaper) than BJTs?

Thanks,

Michael

 

[Tim Wescott]

On Wed, 17 May 2017 09:40:57 -0700, mrdarrett wrote:

On Tuesday, May 16, 2017 at 8:30:26 PM UTC-7, John Larkin wrote:
On Tue, 16 May 2017 12:42:58 -0700 (PDT), mrdarrett@gmail.com wrote:

On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote:
On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote:

Hello,

I've discovered logic-level mosfets, and am using an Arduino to
drive a small 12VDC (about an amp or so) pump motor with PWM,
using an IRLZ34N as the power mosfet.

Would a mosfet-driver be recommended to switch that mosfet on and
off more quickly? Or is a logic-level mosfet already designed to
efficiently turn on and off with the weak logic level signal?

Given that you are also asking about BJT vs. FET, note that in order
to switch at it's fastest, a BJT needs a base driver that can push
charge in quickly and actively pull it out quickly. The difference
in recovery from saturation when you pull the base below ground vs.
when you just pull it _to_ ground can be dramatic.

And don't use a grotty old TIP31 if you want speed -- Zetex
developed some pretty impressive modern BJTs before they got bought
by Diodes, Inc., and turned into a cash cow. Those transistors are
still sold, and have some pretty impressive HFE_sat and VCE_sat
numbers.

--

Tim Wescott Wescott Design Services http://www.wescottdesign.com

I'm looking for work -- see my website!


This is an interesting article. It does mention pulling the base to
-1V. Is this the article you were referring to?

https://www.diodes.com/assets/App-Note-Files/zetex/an14.pdf

Also noteworthy:

"This isn't to exclude MOSFET based designs (some IC vendors have
specified MOS as this suits their technology) but in terms of
equivalent on-resistance and silicon efficiency, the low voltage
bipolar device has no equal. For example, the ZETEX ZTX849 E-Line
(TO-92 compatible) transistor exhibits a RCE(sat) of 36m?. This can
only be matched by a much larger (and expensive) MOSFET die, only
available in TO-220, D-Pak, and similar larger packages."

Michael

That's kinda old. Actually, very old. There are some milliohm mosfets
around now.

https://www.digikey.com/product-detail/en/alpha-omega-semiconductor-
inc/AO3416/785-1011-2-ND/1855783



--

John Larkin Highland Technology, Inc

lunatic fringe electronics


Oh nice!

From the datasheet, Vgs,th,max = 1.1V. This should work fine as a
logic-level mosfet, then?

http://aosmd.com/res/data_sheets/AO3416.pdf

In general, for PWM at 1-2A, 12-18VDC, are mosfets preferred (lower
resistance, cheaper) than BJTs?

AFAIK FETs have pretty much taken over any space where BJTs were once
useful as switching power devices. Once you get above the convenient
operating voltage of FETs, you start seeing IGBTs and SCRs. There may be
some fringe applications, and some older circuits that are still being
shamelessly copied (photoflash units come to mind), but by and large I
think that the BJT has had its day for this.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[rickman]

On 5/16/2017 1:59 PM, Tim Wescott wrote:

On Tue, 16 May 2017 09:22:59 -0700, mrdarrett wrote:


You might have to write another book! I took a peek at your Controls
book and I had no idea Scilab was free. A free Matlab clone, huh?

Michael

BETTER than Matlab. For a certain meaning of "better" (it's not
compatible), but I like it.

People keep trying to tell me to use Python for scientific computation,
and I keep stabbing at learning it, only to gag at learning yet another
interpreted language (and, I'm sorry, indentation should NOT tell the
compiler what the program structure is -- that's simply nuts).

I know a variation of Forth that uses color for syntax. There are modes
of execution of the code. Some code is executed by the editor, some by
the compiler and some is run time. They are all distinguished by color
(along with some other categories like comments).

Oddly enough it is called... ColorForth (written with "color" in red
and "Forth" in green).

--

Rick C

 

[Tim Wescott]

On Wed, 17 May 2017 13:53:05 -0400, rickman wrote:

On 5/16/2017 1:59 PM, Tim Wescott wrote:
On Tue, 16 May 2017 09:22:59 -0700, mrdarrett wrote:


You might have to write another book! I took a peek at your Controls
book and I had no idea Scilab was free. A free Matlab clone, huh?

Michael

BETTER than Matlab. For a certain meaning of "better" (it's not
compatible), but I like it.

People keep trying to tell me to use Python for scientific computation,
and I keep stabbing at learning it, only to gag at learning yet another
interpreted language (and, I'm sorry, indentation should NOT tell the
compiler what the program structure is -- that's simply nuts).

I know a variation of Forth that uses color for syntax. There are modes
of execution of the code. Some code is executed by the editor, some by
the compiler and some is run time. They are all distinguished by color
(along with some other categories like comments).

Oddly enough it is called... ColorForth (written with "color" in red
and "Forth" in green).

Eeew.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[John Larkin]

On Wed, 17 May 2017 09:40:57 -0700 (PDT), mrdarrett@gmail.com wrote:

On Tuesday, May 16, 2017 at 8:30:26 PM UTC-7, John Larkin wrote:
On Tue, 16 May 2017 12:42:58 -0700 (PDT), mrdarrett@gmail.com wrote:

On Monday, May 15, 2017 at 10:37:52 AM UTC-7, Tim Wescott wrote:
On Mon, 15 May 2017 08:33:58 -0700, mrdarrett wrote:

Hello,

I've discovered logic-level mosfets, and am using an Arduino to drive a
small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N
as the power mosfet.

Would a mosfet-driver be recommended to switch that mosfet on and off
more quickly? Or is a logic-level mosfet already designed to
efficiently turn on and off with the weak logic level signal?

Given that you are also asking about BJT vs. FET, note that in order to
switch at it's fastest, a BJT needs a base driver that can push charge in
quickly and actively pull it out quickly. The difference in recovery
from saturation when you pull the base below ground vs. when you just
pull it _to_ ground can be dramatic.

And don't use a grotty old TIP31 if you want speed -- Zetex developed
some pretty impressive modern BJTs before they got bought by Diodes,
Inc., and turned into a cash cow. Those transistors are still sold, and
have some pretty impressive HFE_sat and VCE_sat numbers.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!


This is an interesting article. It does mention pulling the base to -1V. Is this the article you were referring to?

https://www.diodes.com/assets/App-Note-Files/zetex/an14.pdf

Also noteworthy:

"This isn't to exclude MOSFET based designs (some IC vendors have specified MOS as this suits their technology) but in terms of equivalent on-resistance and silicon efficiency, the low voltage bipolar device has no equal. For example, the ZETEX ZTX849 E-Line (TO-92 compatible) transistor exhibits a RCE(sat) of 36m?. This can only be matched by a much larger (and expensive) MOSFET die, only
available in TO-220, D-Pak, and similar larger packages."

Michael

That's kinda old. Actually, very old. There are some milliohm mosfets
around now.

https://www.digikey.com/product-detail/en/alpha-omega-semiconductor-inc/AO3416/785-1011-2-ND/1855783



--

John Larkin Highland Technology, Inc

lunatic fringe electronics


Oh nice!

From the datasheet, Vgs,th,max = 1.1V. This should work fine as a logic-level mosfet, then?

http://aosmd.com/res/data_sheets/AO3416.pdf

If you have 2.5V of gate drive, that makes <26 mohms ON resistance.
3.3 volts, even lower.

If there is a possibility that your drive port could go hi-Z (like
maybe a uP port that's not configured at powerup) a resistor from gate
to ground, 10K or something, would be prudent.

In general, for PWM at 1-2A, 12-18VDC, are mosfets preferred (lower resistance, cheaper) than BJTs?

Thanks,

Michael

I sure prefer them. I rarely use bipolar transistors these days. Maybe
exotica like emitter followers or cascodes or something. Bipolars do
have lower capacitances, which sometimes matters. But for power
switching, mosfets are great.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

On Wednesday, May 17, 2017 at 11:33:56 AM UTC-7, Tim Wescott wrote:

On Wed, 17 May 2017 13:53:05 -0400, rickman wrote:

On 5/16/2017 1:59 PM, Tim Wescott wrote:
On Tue, 16 May 2017 09:22:59 -0700, mrdarrett wrote:


You might have to write another book! I took a peek at your Controls
book and I had no idea Scilab was free. A free Matlab clone, huh?

Michael

BETTER than Matlab. For a certain meaning of "better" (it's not
compatible), but I like it.

People keep trying to tell me to use Python for scientific computation,
and I keep stabbing at learning it, only to gag at learning yet another
interpreted language (and, I'm sorry, indentation should NOT tell the
compiler what the program structure is -- that's simply nuts).

I know a variation of Forth that uses color for syntax. There are modes
of execution of the code. Some code is executed by the editor, some by
the compiler and some is run time. They are all distinguished by color
(along with some other categories like comments).

Oddly enough it is called... ColorForth (written with "color" in red
and "Forth" in green).

Eeew.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

It would be a nightmare for those of us who are moderately color blind

I can barely tell the yeasts apart on page 12.
http://www.fermentis.com/brewing/craftbrewing/tips-tricks/

Michael

 

On Wednesday, May 17, 2017 at 11:37:22 AM UTC-7, John Larkin wrote:

*squish*

That's kinda old. Actually, very old. There are some milliohm mosfets
around now.

https://www.digikey.com/product-detail/en/alpha-omega-semiconductor-inc/AO3416/785-1011-2-ND/1855783



--

John Larkin Highland Technology, Inc

lunatic fringe electronics


Oh nice!

From the datasheet, Vgs,th,max = 1.1V. This should work fine as a logic-level mosfet, then?

http://aosmd.com/res/data_sheets/AO3416.pdf

If you have 2.5V of gate drive, that makes <26 mohms ON resistance.
3.3 volts, even lower.

If there is a possibility that your drive port could go hi-Z (like
maybe a uP port that's not configured at powerup) a resistor from gate
to ground, 10K or something, would be prudent.


In general, for PWM at 1-2A, 12-18VDC, are mosfets preferred (lower resistance, cheaper) than BJTs?

Thanks,

Michael

I sure prefer them. I rarely use bipolar transistors these days. Maybe
exotica like emitter followers or cascodes or something. Bipolars do
have lower capacitances, which sometimes matters. But for power
switching, mosfets are great.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Cool! Thanks!

Michael

 

[John Larkin]

On Wed, 17 May 2017 11:41:42 -0700 (PDT), mrdarrett@gmail.com wrote:

On Wednesday, May 17, 2017 at 11:33:56 AM UTC-7, Tim Wescott wrote:
On Wed, 17 May 2017 13:53:05 -0400, rickman wrote:

On 5/16/2017 1:59 PM, Tim Wescott wrote:
On Tue, 16 May 2017 09:22:59 -0700, mrdarrett wrote:


You might have to write another book! I took a peek at your Controls
book and I had no idea Scilab was free. A free Matlab clone, huh?

Michael

BETTER than Matlab. For a certain meaning of "better" (it's not
compatible), but I like it.

People keep trying to tell me to use Python for scientific computation,
and I keep stabbing at learning it, only to gag at learning yet another
interpreted language (and, I'm sorry, indentation should NOT tell the
compiler what the program structure is -- that's simply nuts).

I know a variation of Forth that uses color for syntax. There are modes
of execution of the code. Some code is executed by the editor, some by
the compiler and some is run time. They are all distinguished by color
(along with some other categories like comments).

Oddly enough it is called... ColorForth (written with "color" in red
and "Forth" in green).

Eeew.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com


It would be a nightmare for those of us who are moderately color blind

Forth is a nightmare no matter what your vision.

I can barely tell the yeasts apart on page 12.
http://www.fermentis.com/brewing/craftbrewing/tips-tricks/

Michael

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[rickman]

On 5/17/2017 2:41 PM, mrdarrett@gmail.com wrote:

On Wednesday, May 17, 2017 at 11:33:56 AM UTC-7, Tim Wescott wrote:
On Wed, 17 May 2017 13:53:05 -0400, rickman wrote:

On 5/16/2017 1:59 PM, Tim Wescott wrote:
On Tue, 16 May 2017 09:22:59 -0700, mrdarrett wrote:


You might have to write another book! I took a peek at your Controls
book and I had no idea Scilab was free. A free Matlab clone, huh?

Michael

BETTER than Matlab. For a certain meaning of "better" (it's not
compatible), but I like it.

People keep trying to tell me to use Python for scientific computation,
and I keep stabbing at learning it, only to gag at learning yet another
interpreted language (and, I'm sorry, indentation should NOT tell the
compiler what the program structure is -- that's simply nuts).

I know a variation of Forth that uses color for syntax. There are modes
of execution of the code. Some code is executed by the editor, some by
the compiler and some is run time. They are all distinguished by color
(along with some other categories like comments).

Oddly enough it is called... ColorForth (written with "color" in red
and "Forth" in green).

Eeew.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com


It would be a nightmare for those of us who are moderately color blind

Yeah, there's supposed to be some way of getting around that, but I
don't recall. It was written by one person for himself, Chuck Moore.

--

Rick C

 

[rickman]

On 5/17/2017 2:56 PM, John Larkin wrote:

On Wed, 17 May 2017 11:41:42 -0700 (PDT), mrdarrett@gmail.com wrote:

On Wednesday, May 17, 2017 at 11:33:56 AM UTC-7, Tim Wescott wrote:
On Wed, 17 May 2017 13:53:05 -0400, rickman wrote:

On 5/16/2017 1:59 PM, Tim Wescott wrote:
On Tue, 16 May 2017 09:22:59 -0700, mrdarrett wrote:


You might have to write another book! I took a peek at your Controls
book and I had no idea Scilab was free. A free Matlab clone, huh?

Michael

BETTER than Matlab. For a certain meaning of "better" (it's not
compatible), but I like it.

People keep trying to tell me to use Python for scientific computation,
and I keep stabbing at learning it, only to gag at learning yet another
interpreted language (and, I'm sorry, indentation should NOT tell the
compiler what the program structure is -- that's simply nuts).

I know a variation of Forth that uses color for syntax. There are modes
of execution of the code. Some code is executed by the editor, some by
the compiler and some is run time. They are all distinguished by color
(along with some other categories like comments).

Oddly enough it is called... ColorForth (written with "color" in red
and "Forth" in green).

Eeew.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com


It would be a nightmare for those of us who are moderately color blind

Forth is a nightmare no matter what your vision.

From someone who doesn't program. Forth is easy to learn, but you have
to learn it. Funny though. Programming in Forth requires you to start
with the basics (it doesn't have arrays built in for example, but they
are easy to create, very easy) but can be very powerful opening the full
potential of the system you are running on. That strikes me as
analogous to the way JL does analog. I guess when it comes to things he
doesn't understand he expects it all to have been done for him.

--

Rick C

 

[Jasen Betts]

On 2017-05-16, Tim Wescott <seemywebsite@myfooter.really> wrote:

On Tue, 16 May 2017 05:01:34 -0400, default wrote:

On Mon, 15 May 2017 12:02:39 -0700 (PDT), mrdarrett@gmail.com wrote:

https://en.wikipedia.org/wiki/Baker_clamp

That's not at all what I was referring to. Zetex (or somebody) figured
out that you could go ahead and let the transistor saturate, but still
get significantly faster turn-off if you actively drew the carriers out
of the base.

maybe just stick the right capacitor in parallel with the base or with
most of the base resistance.

--
This email has not been checked by half-arsed antivirus software

 

[amdx]

On 5/15/2017 10:33 AM, mrdarrett@gmail.com wrote:

Hello,

I've discovered logic-level mosfets, and am using an Arduino to drive a small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N as the power mosfet.

Would a mosfet-driver be recommended to switch that mosfet on and off more quickly? Or is a logic-level mosfet already designed to efficiently turn on and off with the weak logic level signal?

Thanks,

Michael

This doesn't sound like a very critical application.
So it might be overkill, have you looked at the TC4420 series of
FET drivers.
> http://www.learn-c.com/tc4429.pdf

Mikek