mosfet driver needed for logic-level mosfets?

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

 

[Tim Wescott]

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?

You need to do some (gasp!) engineering. You need to know how quickly
the FET needs to turn on and off, you need to know the FET's total gate
charge, and you need to know how much current the processor pins can
supply.

For slow-enough PWM, no, you don't need a driver. Otherwise, yes, you do
-- and you want to be careful to get a driver that has close to rail-rail
output. Some of the oldy-goldie ones have bipolar drive sections with
considerable (up to 1.5V) drop from supply voltage to gate drive. So --
even more engineering.

--
www.wescottdesign.com

 

[Tim Wescott]

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!

 

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?

Which EE classes are these topics discussed in? Can you recommend a book or two?

Thanks,

Michael

 

[Jim Thompson]

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.

Which EE classes are these topics discussed in? Can you recommend a book or two?

Thanks,

Michael

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Thinking outside the box... producing elegant solutions.

"It is not in doing what you like, but in liking what you do that
is the secret of happiness." -James Barrie

 

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

 

[Tim Wescott]

On Mon, 15 May 2017 11:58:31 -0700, 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.

Yea verily.

Which EE classes are these topics discussed in? Can you recommend a
book or two?

None that I know of, and no, in that order. That doesn't mean that
someone else may be more helpful -- just that I don't know.

I learned the technique from Zetex applications notes about 20 years ago;
I used it in a prototype and never used it again.

You can get a nicely controlled negative-going spike at the leading edge
of your base drive with an RC network from your driver, or, if you want
nice behavior over a wider range of duty cycles, a resistor-diode-cap
network. It's all complercated and I can't remember the details and by
God I hope there are still app notes floating around.

The basic idea is that if you just pull the base to ground then the
residual charges that are in the base making it conduct have to
recombine, and you have to wait. If you yank them out by force then --
they're not there any more.

--

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

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

 

[default]

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

 

[George Herold]

On Monday, May 15, 2017 at 2:33:12 PM UTC-4, mrda...@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?

Which EE classes are these topics discussed in? Can you recommend a book or two?

"Practical Electronics for Inventors" is a good basic electronics book,
(and the price is right.) after that go to AoE3.

George H.

Thanks,

Michael

 

On Monday, May 15, 2017 at 9:59:54 PM UTC-7, Tim Wescott wrote:

On Mon, 15 May 2017 11:58:31 -0700, 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.

Yea verily.

Which EE classes are these topics discussed in? Can you recommend a
book or two?

None that I know of, and no, in that order. That doesn't mean that
someone else may be more helpful -- just that I don't know.

I learned the technique from Zetex applications notes about 20 years ago;
I used it in a prototype and never used it again.

You can get a nicely controlled negative-going spike at the leading edge
of your base drive with an RC network from your driver, or, if you want
nice behavior over a wider range of duty cycles, a resistor-diode-cap
network. It's all complercated and I can't remember the details and by
God I hope there are still app notes floating around.

The basic idea is that if you just pull the base to ground then the
residual charges that are in the base making it conduct have to
recombine, and you have to wait. If you yank them out by force then --
they're not there any more.

--

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

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

Huh. I have to check out Zetex. Thanks.

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

 

On Tuesday, May 16, 2017 at 6:00:58 AM UTC-7, George Herold wrote:

On Monday, May 15, 2017 at 2:33:12 PM UTC-4, mrda...@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?

Which EE classes are these topics discussed in? Can you recommend a book or two?
"Practical Electronics for Inventors" is a good basic electronics book,
(and the price is right.) after that go to AoE3.

George H.

Thanks,

Michael

Cool! Thanks!

Michael

 

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

 

[Jim Thompson]

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.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Thinking outside the box... producing elegant solutions.

"It is not in doing what you like, but in liking what you do that
is the secret of happiness." -James Barrie

 

[default]

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

 

[default]

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

Check out all the variations... Seems to me I remember another Baker
switch that returned the base to a negative voltage to suck the
voltage down faster - but it was Fred Baker, from Motorola, not
Richard, and this was all state of the art stuff in the 70's, to drive
plasma panel displays at very high refresh rates. For merely driving
a motor with PWM chances are you don't need to get fancy at all.

I had an application (triggering a camera to power up take a pix then
go back to sleep) running on flea-power batteries. I used one I/O pin
of the controller to run a simple 20 KHZ inductor flyback booster, to
raise the 3V battery supply to 12V, to just provide mosfet bias - so I
didn't need a logic level device and it worked very well.

I clamped the voltage at 12V but it would eventually get to ~50V if I
didn't have a load or clamp the bias power supply.

 

[Tim Wescott]

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

On Monday, May 15, 2017 at 9:59:54 PM UTC-7, Tim Wescott wrote:
On Mon, 15 May 2017 11:58:31 -0700, 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.

Yea verily.

Which EE classes are these topics discussed in? Can you recommend a
book or two?

None that I know of, and no, in that order. That doesn't mean that
someone else may be more helpful -- just that I don't know.

I learned the technique from Zetex applications notes about 20 years
ago;
I used it in a prototype and never used it again.

You can get a nicely controlled negative-going spike at the leading
edge of your base drive with an RC network from your driver, or, if you
want nice behavior over a wider range of duty cycles, a
resistor-diode-cap network. It's all complercated and I can't remember
the details and by God I hope there are still app notes floating
around.

The basic idea is that if you just pull the base to ground then the
residual charges that are in the base making it conduct have to
recombine, and you have to wait. If you yank them out by force then --
they're not there any more.

--

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

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


Huh. I have to check out Zetex. Thanks.

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).

--

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

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

 

[Tim Wescott]

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.

--

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

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

 

[Jim Thompson]

On Tue, 16 May 2017 12:59:36 -0500, Tim Wescott
<seemywebsite@myfooter.really> wrote:

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

On Monday, May 15, 2017 at 9:59:54 PM UTC-7, Tim Wescott wrote:
On Mon, 15 May 2017 11:58:31 -0700, 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.

Yea verily.

Which EE classes are these topics discussed in? Can you recommend a
book or two?

None that I know of, and no, in that order. That doesn't mean that
someone else may be more helpful -- just that I don't know.

I learned the technique from Zetex applications notes about 20 years
ago;
I used it in a prototype and never used it again.

You can get a nicely controlled negative-going spike at the leading
edge of your base drive with an RC network from your driver, or, if you
want nice behavior over a wider range of duty cycles, a
resistor-diode-cap network. It's all complercated and I can't remember
the details and by God I hope there are still app notes floating
around.

The basic idea is that if you just pull the base to ground then the
residual charges that are in the base making it conduct have to
recombine, and you have to wait. If you yank them out by force then --
they're not there any more.

--

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

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


Huh. I have to check out Zetex. Thanks.

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).

As a heavily Algebra-oriented guy I find that I can simply write the
equation in a PSpice behavioral block and solve faster than I can
think bass-ackwards programming ;-)

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Thinking outside the box... producing elegant solutions.

"It is not in doing what you like, but in liking what you do that
is the secret of happiness." -James Barrie

 

[Tim Wescott]

On Mon, 15 May 2017 12:37:45 -0500, 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.

Just for chuckles, here's a demonstration circuit (very much
demonstration only). Set the "inital" voltage on V2 to 0 and compare the
transistor turn-off time: I get about a 10:1 difference.

Version 4
SHEET 1 880 680
WIRE 240 16 -160 16
WIRE 240 48 240 16
WIRE -160 112 -160 16
WIRE -32 144 -64 144
WIRE 80 144 48 144
WIRE 160 144 144 144
WIRE 240 144 240 128
WIRE 368 144 240 144
WIRE 592 144 432 144
WIRE 656 144 592 144
WIRE 768 144 736 144
WIRE 240 176 240 144
WIRE 592 192 592 144
WIRE -160 224 -160 192
WIRE -64 224 -64 144
WIRE 32 224 -64 224
WIRE 160 224 160 144
WIRE 160 224 112 224
WIRE 176 224 160 224
WIRE 768 240 768 144
WIRE -64 256 -64 224
WIRE -64 368 -64 336
WIRE 240 368 240 272
WIRE 592 368 592 256
WIRE 768 368 768 304
FLAG -160 224 0
FLAG 240 368 0
FLAG -64 368 0
FLAG 592 368 0
FLAG 768 368 0
SYMBOL npn 176 176 R0
SYMATTR InstName Q1
SYMATTR Value 2N2222
SYMBOL ind 224 32 R0
SYMATTR InstName L1
SYMATTR Value 120ᚁ
SYMBOL voltage -160 96 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 5
SYMBOL voltage -64 240 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value PULSE(-2 5 0 10n 10n 7u 10u)
SYMBOL cap 576 192 R0
SYMATTR InstName C1
SYMATTR Value 1ᚁ
SYMBOL res 752 128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 50
SYMBOL zener 784 304 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D1
SYMATTR Value BZX84C10L
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 128 208 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 220
SYMBOL schottky 368 160 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D2
SYMATTR Value MBR0530L
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL diode 144 128 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName D3
SYMATTR Value MBR0530L
SYMBOL res 64 128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 10
TEXT -82 392 Left 2 !.tran 100m


--

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

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

 

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