I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.

TIA

Bob

On Wed, 24 Feb 2016 18:29:07 +0000, Bob Minchin
wrote:

I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.


Isn't the external diode there to absorb back-emf's so if the Fet has
one built in similarly connected, does it offer the same level of
protection?

Cheers, T i m

T i m wrote:
On Wed, 24 Feb 2016 18:29:07 +0000, Bob Minchin
wrote:

I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.


Isn't the external diode there to absorb back-emf's so if the Fet has
one built in similarly connected, does it offer the same level of
protection?

Cheers, T i m

Well this is the basis of my question. I would expect the integral diode
to be rated to be man enough to protect the device - otherwise why put
it in? The schematic shows it as a zener diode so it should clamp at or
around the maximum drain source voltage in zener mode and when forward
biassed it should absorb the back emf.
The H bridge circuit is only showing cooking grade 1n4004 diodes which
are not fast types and so might not catch fast voltage spikes

On Wed, 24 Feb 2016 20:27:15 +0000, Bob Minchin
wrote:

T i m wrote:
On Wed, 24 Feb 2016 18:29:07 +0000, Bob Minchin
wrote:

I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.


Isn't the external diode there to absorb back-emf's so if the Fet has
one built in similarly connected, does it offer the same level of
protection?

Cheers, T i m

Well this is the basis of my question. I would expect the integral diode
to be rated to be man enough to protect the device - otherwise why put
it in?

Well, I'm not sure something like that could know what size of (say)
back-emf the device might be exposed to but something could be better
than nothing?

The schematic shows it as a zener diode so it should clamp at or
around the maximum drain source voltage in zener mode and when forward
biassed it should absorb the back emf.

Makes sense.

The H bridge circuit is only showing cooking grade 1n4004 diodes which
are not fast types and so might not catch fast voltage spikes

Isn't it 'Schottky' diodes that are the fast ones (I was a support
tech not a design engineer). ;-)

I used some little IC / integrated bridges with the Arduino project
recently that were both very cheap and worked very well but only good
for the PWM'd amp or so a OO gauge model train would pull. ;-)

Sorry I can't be of any help.

Cheers, T i m

T i m wrote:
On Wed, 24 Feb 2016 20:27:15 +0000, Bob Minchin
wrote:

T i m wrote:
On Wed, 24 Feb 2016 18:29:07 +0000, Bob Minchin
wrote:

I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.


Isn't the external diode there to absorb back-emf's so if the Fet has
one built in similarly connected, does it offer the same level of
protection?

Cheers, T i m

Well this is the basis of my question. I would expect the integral diode
to be rated to be man enough to protect the device - otherwise why put
it in?

Well, I'm not sure something like that could know what size of (say)
back-emf the device might be exposed to but something could be better
than nothing?

The schematic shows it as a zener diode so it should clamp at or
around the maximum drain source voltage in zener mode and when forward
biassed it should absorb the back emf.

Makes sense.

The H bridge circuit is only showing cooking grade 1n4004 diodes which
are not fast types and so might not catch fast voltage spikes

Isn't it 'Schottky' diodes that are the fast ones (I was a support
tech not a design engineer). ;-)

I used some little IC / integrated bridges with the Arduino project
recently that were both very cheap and worked very well but only good
for the PWM'd amp or so a OO gauge model train would pull. ;-)

Sorry I can't be of any help.

Cheers, T i m



Thanks for responding Tim. I've used the integrated H bridges for
driving stepper motors as well as bought in drives but this is my first
experience of driving a golf cart motor with discrete devices for a project.
I'm not short of space and so I can easily fit external diodes - I just
like to try and understand what I'm doing!
Yes Schotty diode are the faster ones. In the 1N400x series the suffix
UF indicates the fast ones eg 1N4004UF. They tend to get used in switch
mode PSUs

In article ,
Bob Minchin writes:
T i m wrote:
On Wed, 24 Feb 2016 18:29:07 +0000, Bob Minchin
wrote:

I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.


Isn't the external diode there to absorb back-emf's so if the Fet has
one built in similarly connected, does it offer the same level of
protection?

Cheers, T i m

Well this is the basis of my question. I would expect the integral diode
to be rated to be man enough to protect the device - otherwise why put
it in? The schematic shows it as a zener diode so it should clamp at or
around the maximum drain source voltage in zener mode and when forward
biassed it should absorb the back emf.
The H bridge circuit is only showing cooking grade 1n4004 diodes which
are not fast types and so might not catch fast voltage spikes

The internal diode is there by accident - the device can't be made
without it. However, it can carry the full load current without any
problems, although it has a higher voltage drop, so power dissipation
is a consideration if you actually plan on using it (as I have in
a mains switching application). Because it's a big diode, it has a
poor recovery time, but that's only relevant at high frequencies.
I would not rely on it's zener properties, and they aren't there to
protect the device.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 24/02/16 22:06, Andrew Gabriel wrote:
The internal diode is there by accident - the device can't be made
without it. However, it can carry the full load current without any
problems,


I'd be very very wary of that.



--
Future generations will wonder in bemused amazement that the early
twenty-first centurys developed world went into hysterical panic over a
globally average temperature increase of a few tenths of a degree, and,
on the basis of gross exaggerations of highly uncertain computer
projections combined into implausible chains of inference, proceeded to
contemplate a rollback of the industrial age.

Richard Lindzen

On 24/02/2016 20:27, Bob Minchin wrote:
T i m wrote:
On Wed, 24 Feb 2016 18:29:07 +0000, Bob Minchin
wrote:

I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.


Isn't the external diode there to absorb back-emf's so if the Fet has
one built in similarly connected, does it offer the same level of
protection?

Cheers, T i m

Well this is the basis of my question. I would expect the integral diode
to be rated to be man enough to protect the device - otherwise why put
it in?

It's not 'put in' as such, it's there as a sort of 'side effect' of the
way these are made. It's called a 'body diode' and its characteristics
are on the data sheet. The forward drop is fairly high, so beware of
power dissipation if you rely on this.

BTW, isn't IRF5305 a P channel?

The schematic shows it as a zener diode so it should clamp at or
around the maximum drain source voltage in zener mode and when forward
biassed it should absorb the back emf.
The H bridge circuit is only showing cooking grade 1n4004 diodes which
are not fast types and so might not catch fast voltage spikes

Cheers
--
Syd

On 25/02/2016 10:14, Syd Rumpo wrote:

snip

Just seen that Andrew Gabriel said much the same, sorry for the repetition.

Cheers
--
Syd

Syd Rumpo wrote:
BTW, isn't IRF5305 a P channel?
Quite correct Syd

I got my Ns & Ps reversed!

Bob

I'd imagine the external diode is going to be more beefy than the internal
one, for a few pence why take the risk?
I've often wondered if one could harvest this back EMF and do something
useful with it.
Brian

"T i m" wrote in message
...
On Wed, 24 Feb 2016 18:29:07 +0000, Bob Minchin
wrote:

I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.


Isn't the external diode there to absorb back-emf's so if the Fet has
one built in similarly connected, does it offer the same level of
protection?

Cheers, T i m

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!

On 24/02/16 18:29, Bob Minchin wrote:
I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.

TIA

Bob
Why dont you just go and buy a model racing car/robot motor controller?

But yeas, you need an external diode. The internal one is parasitic and
not capable of much current.



--
He who ****s in the road, will meet flies on his return.

"Mr Natural"

The Natural Philosopher wrote:
On 24/02/16 18:29, Bob Minchin wrote:
I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.

TIA

Bob
Why dont you just go and buy a model racing car/robot motor controller?

But yeas, you need an external diode. The internal one is parasitic and
not capable of much current.



OK thanks for that.

On 24/02/2016 21:29, The Natural Philosopher wrote:
On 24/02/16 18:29, Bob Minchin wrote:
I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.

TIA

Bob
Why dont you just go and buy a model racing car/robot motor controller?

But yeas, you need an external diode. The internal one is parasitic and
not capable of much current.

What would you say is not "much current"? 1Amp, 2Amps, 10Amps, 50Amps?

What's the rated current of a 1N4004? [1]

What's the continuous Source-Drain Diode Current for the N-channel
IRFZ40? [2]

What's the continuous Source-Drain Diode Current for the P-channel
IRF9Z30? [3]

Are you suggesting continuously rated current of [1] is less than that
of [2] and [3]?

[1] http://www.diodes.com/_files/datasheets/ds28002.pdf (1Amp)
[2] http://www.vishay.com/docs/91385/sihfz40.pdf (50Amps)
[3] http://www.vishay.com/docs/91459/sihf9z30.pdf (18Amps)

--
A closed mouth gathers no foot.

On 24/02/2016 21:29, The Natural Philosopher wrote:
On 24/02/16 18:29, Bob Minchin wrote:
I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.

TIA

Bob
Why dont you just go and buy a model racing car/robot motor controller?

But yeas, you need an external diode. The internal one is parasitic and
not capable of much current.

That's incorrect, both parts show 30A continuous, 110A pulsed for the
body diode, about the same as the drain current.

Cheers
--
Syd

On 24/02/2016 18:29, Bob Minchin wrote:
I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.

To me the 1N4004 diodes seem entirely superfluous. The internal Drain
Source diode is far meatier than any 1n4001. Plus it can dissipate any
transient energy with ease.

The bit that worries me is the driving of these gates. The level
translator is all well and good, but the biggest concern is how to not
overlap the gate drives to ensure that no n and p channels MOSFETs are
conducting at the same time.

10k is considered large in comparison with gate charge of 10s of nC
leading to an extended on and off times.

Fredxxx wrote:
On 24/02/2016 18:29, Bob Minchin wrote:
I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.

To me the 1N4004 diodes seem entirely superfluous. The internal Drain
Source diode is far meatier than any 1n4001. Plus it can dissipate any
transient energy with ease.

The bit that worries me is the driving of these gates. The level
translator is all well and good, but the biggest concern is how to not
overlap the gate drives to ensure that no n and p channels MOSFETs are
conducting at the same time.

10k is considered large in comparison with gate charge of 10s of nC
leading to an extended on and off times.

I see your point. In my application reversing will be quite infrequent
so should not be an issue.

On 24/02/2016 21:44, Bob Minchin wrote:
Fredxxx wrote:
On 24/02/2016 18:29, Bob Minchin wrote:
I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.

To me the 1N4004 diodes seem entirely superfluous. The internal Drain
Source diode is far meatier than any 1n4001. Plus it can dissipate any
transient energy with ease.

The bit that worries me is the driving of these gates. The level
translator is all well and good, but the biggest concern is how to not
overlap the gate drives to ensure that no n and p channels MOSFETs are
conducting at the same time.

10k is considered large in comparison with gate charge of 10s of nC
leading to an extended on and off times.

I see your point. In my application reversing will be quite infrequent
so should not be an issue.

How will you ensure the upper and lower MOSFETs can never be turned on
simultaneously?

What voltage and current is your application?

Would something like this make your life so much easier?

http://uk.farnell.com/stmicroelectro...tor/dp/2475457

Datasheet for IC:
http://www.farnell.com/datasheets/1902055.pdf

On Wed, 24 Feb 2016 23:57:47 +0000, Fredxxx wrote:

snip

Would something like this make your life so much easier?

http://uk.farnell.com/stmicroelectro...tor/dp/2475457

Datasheet for IC:
http://www.farnell.com/datasheets/1902055.pdf


Or this could be easier still. ;-)

http://preview.tinyurl.com/zkc9ljz

Cheers, T i m

T i m wrote:
On Wed, 24 Feb 2016 23:57:47 +0000, Fredxxx wrote:

snip

Would something like this make your life so much easier?

http://uk.farnell.com/stmicroelectro...tor/dp/2475457

Datasheet for IC:
http://www.farnell.com/datasheets/1902055.pdf


Or this could be easier still. ;-)

http://preview.tinyurl.com/zkc9ljz

Cheers, T i m

That looks quite interesting Tim Thanks
Might be useful if all the smoke escapes from my discrete breadboard in
an instant.

A few comments
1) I just ordered a load of £1 mosfets from CPC to play with befreo
seeing your post.
2) The ebay seller says no circuit info available - yes I could draw it
out. No terminal blocks either. Doh! why not add a £1 to price and do a
proper job on the pcb build.
3)It says two half bridges - do 2 halves make a whole? Look more like a
stepper driver? I'm not up with the jargon. Also mentions two motors WTF?
4)Only N channel mosfets I think so "top" half o/p won't got to full
supply. I need the full power Igor! This motor powers an elevation
platform for a 1/4 tonne machine.
5)Chinglish description only partially decoded by me so far.
6)Waiting for delivery from H-K etc Wanna play now!!
7)I might not learn as much from a bought in module.

Cheers
Bob

In article ,
Bob Minchin wrote:
I want to use mosfets in an H bridge configuration to control and
reverse a 12v permanent magnet motor - obviously an inductive load.
Running current will be 10amps or so.

The sort of circuit I plan to use is here
http://www.talkingelectronics.com/pr...-Bridge-1.html
Scroll down to design number 6

I'll be using IRF5305 N channel and IRLZ34 P channel devices.

The data sheet for the Mosfets show an internal diode from drain to
source and yet the above circuit (and many other on the web) show an
external catch diode as well.

Is this necessary, a prudent precaution or simply redundant.

Although I've been working in electronics all my working career I was
moved into management and not allowed to do real work before power
mosfets came into common use.

Mosfets and PWM drive are very common on car injection systems. To drive
things like injectors, fuel pumps, idle motors etc. Many use an IC these
days which includes protection etc. Just a thought.

--
*Frustration is trying to find your glasses without your glasses.

Dave Plowman London SW
To e-mail, change noise into sound.