Open the (mosfet) gate!

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as such on the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be FULLY OPEN at 5V... I guess I was wrong..?

Michael

 

[John Larkin]

On Wed, 24 May 2017 08:52:54 -0700 (PDT), mrdarrett@gmail.com wrote:

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as such on the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be FULLY OPEN at 5V... I guess I was wrong..?

Michael

More gate voltage makes for lower Rds-on. It's a linear device, not a
gate or a switch, despite the word "logic."

Don't trust IR specs anyhow. They are notorious for fudging. This one
might be safe at 10 amps and Vg=10 and a heat sink.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

 

On Wednesday, May 24, 2017 at 10:53:53 AM UTC-7, John Larkin wrote:

On Wed, 24 May 2017 08:52:54 -0700 (PDT), mrdarrett@gmail.com wrote:

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as such on the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be FULLY OPEN at 5V... I guess I was wrong..?

Michael

More gate voltage makes for lower Rds-on. It's a linear device, not a
gate or a switch, despite the word "logic."

Don't trust IR specs anyhow. They are notorious for fudging. This one
might be safe at 10 amps and Vg=10 and a heat sink.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

So the moral of the story is, if you want the gate opened *all the way* with minimum Rds,on, give the gate Vgs,max then?

Michael

 

[Ian Field]

<mrdarrett@gmail.com> wrote in message
news:639ab626-0171-492e-b0f7-864e38edcef4@googlegroups.com...

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as such on
the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be FULLY
OPEN at 5V... I guess I was wrong..?

PC motherboard MOSFETs usually switch pretty convincingly with just under 2V
on the gate.

The drain current can be anything up to about 95A, but you're unlikely to
find any rated higher than 30V and a few are only 20V.

 

[George Herold]

On Wednesday, May 24, 2017 at 2:33:04 PM UTC-4, mrda...@gmail.com wrote:

On Wednesday, May 24, 2017 at 10:53:53 AM UTC-7, John Larkin wrote:
On Wed, 24 May 2017 08:52:54 -0700 (PDT), mrdarrett@gmail.com wrote:

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as such on the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be FULLY OPEN at 5V... I guess I was wrong..?

Michael

More gate voltage makes for lower Rds-on. It's a linear device, not a
gate or a switch, despite the word "logic."

Don't trust IR specs anyhow. They are notorious for fudging. This one
might be safe at 10 amps and Vg=10 and a heat sink.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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


So the moral of the story is, if you want the gate opened *all the way* with minimum Rds,on, give the gate Vgs,max then?

Michael

Oh dear, I think we have some nomenclature confusion.
(Or maybe I'm confused.)
When I (we) say the gate is open, that means something like an open
circuit. Rds is infinite (or very large)
When the gate is closed, it's like a closed switch with minimum
Rds.

Your Fet has only 0.01 ohms more resistance at 5V vs 10V. That's
not much at all, and the fet is still basically closed at 5V.
If you are really pushing the limits in terms of heat dissipation then,
yeah a little more gate drive might help.

 

[John Larkin]

On Wed, 24 May 2017 11:32:58 -0700 (PDT), mrdarrett@gmail.com wrote:

On Wednesday, May 24, 2017 at 10:53:53 AM UTC-7, John Larkin wrote:
On Wed, 24 May 2017 08:52:54 -0700 (PDT), mrdarrett@gmail.com wrote:

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as such on the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be FULLY OPEN at 5V... I guess I was wrong..?

Michael

More gate voltage makes for lower Rds-on. It's a linear device, not a
gate or a switch, despite the word "logic."

Don't trust IR specs anyhow. They are notorious for fudging. This one
might be safe at 10 amps and Vg=10 and a heat sink.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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


So the moral of the story is, if you want the gate opened *all the way* with minimum Rds,on, give the gate Vgs,max then?

Michael

Well, "opened" means not conducting to me.

But more gate voltage makes for lower Rds-on, as shown in the graphs
on the data sheet. That part is almost fully enhanced at 10 volts on
the gate.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

 

[rickman]

mrdarrett@gmail.com wrote:

On Wednesday, May 24, 2017 at 10:53:53 AM UTC-7, John Larkin wrote:
On Wed, 24 May 2017 08:52:54 -0700 (PDT), mrdarrett@gmail.com wrote:

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as such on the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be FULLY OPEN at 5V... I guess I was wrong..?


More gate voltage makes for lower Rds-on. It's a linear device, not a
gate or a switch, despite the word "logic."

Don't trust IR specs anyhow. They are notorious for fudging. This one
might be safe at 10 amps and Vg=10 and a heat sink.

So the moral of the story is, if you want the gate opened *all the way* with minimum Rds,on, give the gate Vgs,max then?

Ignoring the poor use of nomenclature, yes, (considering the gate to be
a garden gate) higher Vgs opens the gate wider. There will be a point
of maximum effect or at least diminishing returns, but logic FETs will
turn on at logic level voltages, but turn on more fully at higher
voltages. Just don't get carried away and apply 20 volts to a gate that
is only rated for 10.

--

Rick C

 

On Wednesday, May 24, 2017 at 1:27:57 PM UTC-7, rickman wrote:

mrdarrett@gmail.com wrote:
On Wednesday, May 24, 2017 at 10:53:53 AM UTC-7, John Larkin wrote:
On Wed, 24 May 2017 08:52:54 -0700 (PDT), mrdarrett@gmail.com wrote:

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as such on the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be FULLY OPEN at 5V... I guess I was wrong..?


More gate voltage makes for lower Rds-on. It's a linear device, not a
gate or a switch, despite the word "logic."

Don't trust IR specs anyhow. They are notorious for fudging. This one
might be safe at 10 amps and Vg=10 and a heat sink.

So the moral of the story is, if you want the gate opened *all the way* with minimum Rds,on, give the gate Vgs,max then?

Ignoring the poor use of nomenclature, yes, (considering the gate to be
a garden gate) higher Vgs opens the gate wider. There will be a point
of maximum effect or at least diminishing returns, but logic FETs will
turn on at logic level voltages, but turn on more fully at higher
voltages. Just don't get carried away and apply 20 volts to a gate that
is only rated for 10.

--

Rick C

Ah ok, open means open-circuit.

I'm just imagining the King ordering the guards, "Open the gate!" and they open it to 90% only, and the King bumps his head on the partially-open gate as he rides in on his horse.

Michael

 

On Wednesday, May 24, 2017 at 3:37:02 PM UTC-7, mrda...@gmail.com wrote:

On Wednesday, May 24, 2017 at 1:27:57 PM UTC-7, rickman wrote:
mrdarrett@gmail.com wrote:
On Wednesday, May 24, 2017 at 10:53:53 AM UTC-7, John Larkin wrote:
On Wed, 24 May 2017 08:52:54 -0700 (PDT), mrdarrett@gmail.com wrote:

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as such on the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be FULLY OPEN at 5V... I guess I was wrong..?


More gate voltage makes for lower Rds-on. It's a linear device, not a
gate or a switch, despite the word "logic."

Don't trust IR specs anyhow. They are notorious for fudging. This one
might be safe at 10 amps and Vg=10 and a heat sink.

So the moral of the story is, if you want the gate opened *all the way* with minimum Rds,on, give the gate Vgs,max then?

Ignoring the poor use of nomenclature, yes, (considering the gate to be
a garden gate) higher Vgs opens the gate wider. There will be a point
of maximum effect or at least diminishing returns, but logic FETs will
turn on at logic level voltages, but turn on more fully at higher
voltages. Just don't get carried away and apply 20 volts to a gate that
is only rated for 10.

--

Rick C


Ah ok, open means open-circuit.

I'm just imagining the King ordering the guards, "Open the gate!" and they open it to 90% only, and the King bumps his head on the partially-open gate as he rides in on his horse.

Michael

King: "I said to open the gate!"
Guards: "We did! The specs said it's open!"
King: "OFF WITH HIS HEAD!"

 

[rickman]

mrdarrett@gmail.com wrote on 5/24/2017 6:38 PM:

On Wednesday, May 24, 2017 at 3:37:02 PM UTC-7, mrda...@gmail.com wrote:
On Wednesday, May 24, 2017 at 1:27:57 PM UTC-7, rickman wrote:
mrdarrett@gmail.com wrote:
On Wednesday, May 24, 2017 at 10:53:53 AM UTC-7, John Larkin wrote:
On Wed, 24 May 2017 08:52:54 -0700 (PDT), mrdarrett@gmail.com wrote:

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as such on the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be FULLY OPEN at 5V... I guess I was wrong..?


More gate voltage makes for lower Rds-on. It's a linear device, not a
gate or a switch, despite the word "logic."

Don't trust IR specs anyhow. They are notorious for fudging. This one
might be safe at 10 amps and Vg=10 and a heat sink.

So the moral of the story is, if you want the gate opened *all the way* with minimum Rds,on, give the gate Vgs,max then?

Ignoring the poor use of nomenclature, yes, (considering the gate to be
a garden gate) higher Vgs opens the gate wider. There will be a point
of maximum effect or at least diminishing returns, but logic FETs will
turn on at logic level voltages, but turn on more fully at higher
voltages. Just don't get carried away and apply 20 volts to a gate that
is only rated for 10.

--

Rick C


Ah ok, open means open-circuit.

I'm just imagining the King ordering the guards, "Open the gate!" and they open it to 90% only, and the King bumps his head on the partially-open gate as he rides in on his horse.

Michael


King: "I said to open the gate!"
Guards: "We did! The specs said it's open!"
King: "OFF WITH HIS HEAD!"

lol

--

Rick C

 

[Tim Wescott]

On Wed, 24 May 2017 08:52:54 -0700, mrdarrett wrote:

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as such on
the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be FULLY
OPEN at 5V... I guess I was wrong..?

Michael

That's not atypical of FETs advertised as logic level. The most you can
expect is that if it's called logic level then the data sheet will
specify operation at 5V, and it won't be too stupid (and, these days,
maybe even at 3.3V).

--
www.wescottdesign.com

 

[rickman]

Tim Wescott wrote on 5/24/2017 11:17 PM:

On Wed, 24 May 2017 08:52:54 -0700, mrdarrett wrote:

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as such on
the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be FULLY
OPEN at 5V... I guess I was wrong..?

Michael

That's not atypical of FETs advertised as logic level. The most you can
expect is that if it's called logic level then the data sheet will
specify operation at 5V, and it won't be too stupid (and, these days,
maybe even at 3.3V).

I had asked about logic level FETs in s.e.d not too long ago and I was
pointed to some with threshold voltages in the 1 volt ballpark. The
IRLML6344TRPbF is rated with a typical threshold below 1 volt, passing 1
amp with Vgs less than 1.5 volts and 10 amps with Vgs less than 2 volts.
That's a far cry from needing 5 volts.

--

Rick C

 

[Tim Wescott]

On Thu, 25 May 2017 00:45:01 -0400, rickman wrote:

Tim Wescott wrote on 5/24/2017 11:17 PM:
On Wed, 24 May 2017 08:52:54 -0700, mrdarrett wrote:

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as such
on the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be
FULLY OPEN at 5V... I guess I was wrong..?

Michael

That's not atypical of FETs advertised as logic level. The most you
can expect is that if it's called logic level then the data sheet will
specify operation at 5V, and it won't be too stupid (and, these days,
maybe even at 3.3V).

I had asked about logic level FETs in s.e.d not too long ago and I was
pointed to some with threshold voltages in the 1 volt ballpark. The
IRLML6344TRPbF is rated with a typical threshold below 1 volt, passing 1
amp with Vgs less than 1.5 volts and 10 amps with Vgs less than 2 volts.
That's a far cry from needing 5 volts.

My point is that "logic level" is a nice-sounding, mostly meaningless
name. If you want to trust what the part is going to do, read the data
sheet -- carefully.

I didn't mean that there weren't parts that might work at much lower
voltages -- just that you couldn't go shopping for parts based only on
them being "logic level".

--
www.wescottdesign.com

 

On Monday, May 29, 2017 at 12:17:16 PM UTC-7, Tim Wescott wrote:

On Thu, 25 May 2017 00:45:01 -0400, rickman wrote:

Tim Wescott wrote on 5/24/2017 11:17 PM:
On Wed, 24 May 2017 08:52:54 -0700, mrdarrett wrote:

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as such
on the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be
FULLY OPEN at 5V... I guess I was wrong..?

Michael

That's not atypical of FETs advertised as logic level. The most you
can expect is that if it's called logic level then the data sheet will
specify operation at 5V, and it won't be too stupid (and, these days,
maybe even at 3.3V).

I had asked about logic level FETs in s.e.d not too long ago and I was
pointed to some with threshold voltages in the 1 volt ballpark. The
IRLML6344TRPbF is rated with a typical threshold below 1 volt, passing 1
amp with Vgs less than 1.5 volts and 10 amps with Vgs less than 2 volts.
That's a far cry from needing 5 volts.

My point is that "logic level" is a nice-sounding, mostly meaningless
name. If you want to trust what the part is going to do, read the data
sheet -- carefully.

I didn't mean that there weren't parts that might work at much lower
voltages -- just that you couldn't go shopping for parts based only on
them being "logic level".

--
www.wescottdesign.com

Yes, yes, good point.

I'm wondering if a voltage amplifier could be used to shove 15V or so to the gate... and I could use a cheaper IRF530 / standard MOSFET.

Michael

 

[Tim Wescott]

On Tue, 30 May 2017 13:37:10 -0700, mrdarrett wrote:

On Monday, May 29, 2017 at 12:17:16 PM UTC-7, Tim Wescott wrote:
On Thu, 25 May 2017 00:45:01 -0400, rickman wrote:

Tim Wescott wrote on 5/24/2017 11:17 PM:
On Wed, 24 May 2017 08:52:54 -0700, mrdarrett wrote:

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as
such on the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be
FULLY OPEN at 5V... I guess I was wrong..?

Michael

That's not atypical of FETs advertised as logic level. The most you
can expect is that if it's called logic level then the data sheet
will specify operation at 5V, and it won't be too stupid (and, these
days, maybe even at 3.3V).

I had asked about logic level FETs in s.e.d not too long ago and I
was pointed to some with threshold voltages in the 1 volt ballpark.
The IRLML6344TRPbF is rated with a typical threshold below 1 volt,
passing 1 amp with Vgs less than 1.5 volts and 10 amps with Vgs less
than 2 volts.
That's a far cry from needing 5 volts.

My point is that "logic level" is a nice-sounding, mostly meaningless
name. If you want to trust what the part is going to do, read the data
sheet -- carefully.

I didn't mean that there weren't parts that might work at much lower
voltages -- just that you couldn't go shopping for parts based only on
them being "logic level".

--
www.wescottdesign.com


Yes, yes, good point.

I'm wondering if a voltage amplifier could be used to shove 15V or so to
the gate... and I could use a cheaper IRF530 / standard MOSFET.

If you're just switching the thing on and off, and if you have 12 or 15V
available, you want a gate driver. There's a plethora of them out
there. And lots and lots, too.

--

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

 

On Tuesday, May 30, 2017 at 8:06:00 PM UTC-7, Tim Wescott wrote:

On Tue, 30 May 2017 13:37:10 -0700, mrdarrett wrote:

On Monday, May 29, 2017 at 12:17:16 PM UTC-7, Tim Wescott wrote:
On Thu, 25 May 2017 00:45:01 -0400, rickman wrote:

Tim Wescott wrote on 5/24/2017 11:17 PM:
On Wed, 24 May 2017 08:52:54 -0700, mrdarrett wrote:

I was looking at this datasheet:

http://www.irf.com/product-info/datasheets/data/irlz34n.pdf

Rds,on is 0.035 ohm with Vgs=10V (Id=16A) and it's advertised as
such on the first page.

But at Vgs=5V (Id=16A) the Rds,on is 0.046 ohm!

I thought it was a logic level mosfet; I thought the gate would be
FULLY OPEN at 5V... I guess I was wrong..?

Michael

That's not atypical of FETs advertised as logic level. The most you
can expect is that if it's called logic level then the data sheet
will specify operation at 5V, and it won't be too stupid (and, these
days, maybe even at 3.3V).

I had asked about logic level FETs in s.e.d not too long ago and I
was pointed to some with threshold voltages in the 1 volt ballpark.
The IRLML6344TRPbF is rated with a typical threshold below 1 volt,
passing 1 amp with Vgs less than 1.5 volts and 10 amps with Vgs less
than 2 volts.
That's a far cry from needing 5 volts.

My point is that "logic level" is a nice-sounding, mostly meaningless
name. If you want to trust what the part is going to do, read the data
sheet -- carefully.

I didn't mean that there weren't parts that might work at much lower
voltages -- just that you couldn't go shopping for parts based only on
them being "logic level".

--
www.wescottdesign.com


Yes, yes, good point.

I'm wondering if a voltage amplifier could be used to shove 15V or so to
the gate... and I could use a cheaper IRF530 / standard MOSFET.

If you're just switching the thing on and off, and if you have 12 or 15V
available, you want a gate driver. There's a plethora of them out
there. And lots and lots, too.

--

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

A gate driver would work, but how about this?
https://arduinodiy.files.wordpress.com/2012/05/fet2.gif

Michael

 

[Jim Thompson]

On Wed, 31 May 2017 11:41:33 -0700 (PDT), mrdarrett@gmail.com wrote:

On Tuesday, May 30, 2017 at 8:06:00 PM UTC-7, Tim Wescott wrote:
On Tue, 30 May 2017 13:37:10 -0700, mrdarrett wrote:

[snip]

I'm wondering if a voltage amplifier could be used to shove 15V or so to
the gate... and I could use a cheaper IRF530 / standard MOSFET.

If you're just switching the thing on and off, and if you have 12 or 15V
available, you want a gate driver. There's a plethora of them out
there. And lots and lots, too.

--

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


A gate driver would work, but how about this?
https://arduinodiy.files.wordpress.com/2012/05/fet2.gif

Michael

That works, sort of... beware the slow risetime of the gate voltage,
10K and the gate capacitance might result in substantial dissipation
during turn-on.

...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 Wednesday, May 31, 2017 at 12:22:00 PM UTC-7, Jim Thompson wrote:

On Wed, 31 May 2017 11:41:33 -0700 (PDT), mrdarrett@gmail.com wrote:

On Tuesday, May 30, 2017 at 8:06:00 PM UTC-7, Tim Wescott wrote:
On Tue, 30 May 2017 13:37:10 -0700, mrdarrett wrote:

[snip]

I'm wondering if a voltage amplifier could be used to shove 15V or so to
the gate... and I could use a cheaper IRF530 / standard MOSFET.

If you're just switching the thing on and off, and if you have 12 or 15V
available, you want a gate driver. There's a plethora of them out
there. And lots and lots, too.

--

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


A gate driver would work, but how about this?
https://arduinodiy.files.wordpress.com/2012/05/fet2.gif

Michael

That works, sort of... beware the slow risetime of the gate voltage,
10K and the gate capacitance might result in substantial dissipation
during turn-on.

...Jim Thompson

How slow is slow? Operation would be restricted to below 30kHz, 1kHz, ???

Would increasing the resistor to 47k improve anything?

Michael

 

[Jim Thompson]

On Wed, 31 May 2017 13:11:02 -0700 (PDT), mrdarrett@gmail.com wrote:

On Wednesday, May 31, 2017 at 12:22:00 PM UTC-7, Jim Thompson wrote:
On Wed, 31 May 2017 11:41:33 -0700 (PDT), mrdarrett@gmail.com wrote:

On Tuesday, May 30, 2017 at 8:06:00 PM UTC-7, Tim Wescott wrote:
On Tue, 30 May 2017 13:37:10 -0700, mrdarrett wrote:

[snip]

I'm wondering if a voltage amplifier could be used to shove 15V or so to
the gate... and I could use a cheaper IRF530 / standard MOSFET.

If you're just switching the thing on and off, and if you have 12 or 15V
available, you want a gate driver. There's a plethora of them out
there. And lots and lots, too.

--

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


A gate driver would work, but how about this?
https://arduinodiy.files.wordpress.com/2012/05/fet2.gif

Michael

That works, sort of... beware the slow risetime of the gate voltage,
10K and the gate capacitance might result in substantial dissipation
during turn-on.

...Jim Thompson


How slow is slow? Operation would be restricted to below 30kHz, 1kHz, ???

Would increasing the resistor to 47k improve anything?

Michael

Frequency isn't the main event, it's risetime. You'd have to simulate
with a known MOSFET AND defined load.

...Jim Thompson
--
| James E.Thompson | mens |
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| 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 Wednesday, May 31, 2017 at 4:58:32 PM UTC-7, Jim Thompson wrote:

On Wed, 31 May 2017 13:11:02 -0700 (PDT), mrdarrett@gmail.com wrote:

On Wednesday, May 31, 2017 at 12:22:00 PM UTC-7, Jim Thompson wrote:
On Wed, 31 May 2017 11:41:33 -0700 (PDT), mrdarrett@gmail.com wrote:

On Tuesday, May 30, 2017 at 8:06:00 PM UTC-7, Tim Wescott wrote:
On Tue, 30 May 2017 13:37:10 -0700, mrdarrett wrote:

[snip]

I'm wondering if a voltage amplifier could be used to shove 15V or so to
the gate... and I could use a cheaper IRF530 / standard MOSFET.

If you're just switching the thing on and off, and if you have 12 or 15V
available, you want a gate driver. There's a plethora of them out
there. And lots and lots, too.

--

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


A gate driver would work, but how about this?
https://arduinodiy.files.wordpress.com/2012/05/fet2.gif

Michael

That works, sort of... beware the slow risetime of the gate voltage,
10K and the gate capacitance might result in substantial dissipation
during turn-on.

...Jim Thompson


How slow is slow? Operation would be restricted to below 30kHz, 1kHz, ???

Would increasing the resistor to 47k improve anything?

Michael

Frequency isn't the main event, it's risetime. You'd have to simulate
with a known MOSFET AND defined load.

...Jim Thompson

Since the NPN gate driver inverts the input signal, is there a PNP solution that won't invert it?

Thanks,

Michael