Searching \ for '[EE] Continuous high-side drive' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=continuous+high
Search entire site for: 'Continuous high-side drive'.

Exact match. Not showing close matches.
PICList Thread
'[EE] Continuous high-side drive'
2007\03\26@195629 by Sean Breheny

face picon face
Hi all,

I have a circuit which needs to switch a 48V supply (which can rise as
high as 80V). The load is ground referenced and can draw as much as
100 Amps. The switch, however, need not open while any more than 1 Amp
is flowing.

To accomplish this, I was planning on using several N channel FETs in
parallel (because of their low Rds_on). Because the load can be on for
hours or days, I need a true DC high-side drive (normal bootstrap-type
drivers will not work because the bootstrap cap will discharge
slowly).

Based on a web search, I thought that the Intersil ISL6801 would do
this, but the datasheet is confusing and ambiguous, and my actual
prototype test showed that it cannot handle this situation (acts like
a normal bootstrap driver).

Most of the other ICs I found which claim to do this are limited to
less than 80V at the FET source.

I designed up a circuit to do it using a transformer and optocouplers,
but it is not pretty or cheap.

Anyone know of an IC to do gate drive for something like this?

Thanks,

Sean

2007\03\26@202329 by Brent Brown

picon face
Sean Breheny wrote:
> I have a circuit which needs to switch a 48V supply (which can rise as
> high as 80V). The load is ground referenced and can draw as much as
> 100 Amps. The switch, however, need not open while any more than 1 Amp
> is flowing.
<snip>
> Anyone know of an IC to do gate drive for something like this?

Yes,

The following are an absolutley brilliant invention and not well enough known
(IMHO)...

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

Think of it as an optocoupler with an LED on one side and a solar cell on the other
side. Output voltage is completely isolated. Limited in it's applications by it's output
current and thereby turn on speed when switching MOSFET's. Potentialy (no pun
intended) could be exactly what you need.

--
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  spam_OUTbrent.brownTakeThisOuTspamclear.net.nz


2007\03\26@202857 by Robert Rolf

picon face
Sean Breheny wrote:

> Hi all,
>
> I have a circuit which needs to switch a 48V supply (which can rise as
> high as 80V). The load is ground referenced and can draw as much as
> 100 Amps. The switch, however, need not open while any more than 1 Amp
> is flowing.
>
> To accomplish this, I was planning on using several N channel FETs in
> parallel (because of their low Rds_on). Because the load can be on for
> hours or days, I need a true DC high-side drive (normal bootstrap-type
> drivers will not work because the bootstrap cap will discharge
> slowly).


Why not break your FETs into multiple banks and drive then with a
multiple phase low off duty cycle signal?
You could then use bootstrap drive mode. (clamp diode to give fast
recharge recovery)
If you have 8 Fets, you'd have 1 of 8 off for a few milliseconds
every second so at most you'd need 1 extra Fet to cover the load
of the one that is off.l

> Based on a web search, I thought that the Intersil ISL6801 would do
> this, but the datasheet is confusing and ambiguous, and my actual
> prototype test showed that it cannot handle this situation (acts like
> a normal bootstrap driver).

Huh? The spec sheet says it does DC.

"To ensure static DC operation an integrated recharge path charges the
bootstrap cap while the driver is switched off."


> Most of the other ICs I found which claim to do this are limited to
> less than 80V at the FET source.
>
> I designed up a circuit to do it using a transformer and optocouplers,
> but it is not pretty or cheap.
>
> Anyone know of an IC to do gate drive for something like this?

And you can't use a relay because???
Or bridge the Fets with a relay after their initial operation?

Robert

2007\03\26@202956 by Brent Brown

picon face
Brent Brown wrote:
{Quote hidden}

P.S. For more information check out their application note...

http://www.irf.com/technical-info/appnotes/an-1017.pdf


--
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  .....brent.brownKILLspamspam@spam@clear.net.nz


2007\03\26@203636 by Jake Anderson

flavicon
face
Sean Breheny wrote:
{Quote hidden}

no but I would be interested in which ones you found for < 80v if you
happen to have them handy?

2007\03\26@204027 by peter green

flavicon
face
part 1 1926 bytes content-type:text/plain; (unknown type 8bit not decoded)


> I have a circuit which needs to switch a 48V supply (which can rise as
> high as 80V). The load is ground referenced and can draw as much as
> 100 Amps. The switch, however, need not open while any more than 1 Amp
> is flowing.
>
> To accomplish this, I was planning on using several N channel FETs in
> parallel (because of their low Rds_on). Because the load can be on for
> hours or days, I need a true DC high-side drive (normal bootstrap-type
> drivers will not work because the bootstrap cap will discharge
> slowly).
i think we can solve this one with a variation on the idea of a charge pump.

http://img155.imageshack.us/img155/8071/drivecircuitei5.png

when the square wave is low the pump capacitor charges from the "high" voltage supply when it is low its output is lifted and transferred into the tank capacitor.

hence the tank capacitor output ends up at roughly the supply voltage for the high supply plus the peak to peak of the square wave minus a couple of diode drops and some other inefficiancies.

the two diodes to the supplies for the square wave are to protect the square wave generator during power up and down and probablly need to be shotkeys.

this then powers the pull up for the resistor/transistor buffer allowing it to get above the high voltage supply rail and hence provide and appropriate gate voltage for the main mosfets.

working out component values and simulating this thing is left as an excercise for the implementer, this is an idea only and has not been tested.

note: this circuit may have pathalogical behaviour if the supply voltage varies in step with the square wave driving the pump. This seems pretty unlikely thought
--
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.446 / Virus Database: 268.18.18/733 - Release Date: 25/03/2007 11:07




part 2 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2007\03\26@204734 by John Dammeyer

flavicon
face
Hi Sean,

It's not as difficult with the normal bootstrap drivers as you might
think.  

The High side drivers just need a supply referenced to the Source of the
high side FET that allows them to drive with more than 10V.

We did this for a military project using a 5V to 12V isolated DC to DC
module powering an IR2104.  The output ground of the modules are
connected to the sources of the upper FET in the H-Bridge.  The IR2104
switches this 12V onto the gate of the FET.  

The bootstrap method where the PWM provides the drive voltage is only a
cost saving feature to provide a higher than motor rail voltage.  You
don't have to use it.

John Dammeyer


Automation Artisans Inc.
http://www.autoartisans.com
Ph. 1 250 544 4950


> {Original Message removed}

2007\03\26@205001 by Nate Duehr

face
flavicon
face
On 3/26/07, Sean Breheny <shb7spamKILLspamcornell.edu> wrote:
> Hi all,
>
> I have a circuit which needs to switch a 48V supply (which can rise as
> high as 80V). The load is ground referenced and can draw as much as
> 100 Amps. The switch, however, need not open while any more than 1 Amp
> is flowing.

Telco/Central Office/Inside-plant remote power switches do stuff like
this all the time.

You might want to talk to or look at products like those...
http://www.servertech.com would be one example of many...

Many of these products do just have good "old-fashioned" relays in
them, however... especially for the higher current models.

Nate

2007\03\26@225619 by Sean Breheny
face picon face
Hi Brent,

Thanks! This looks like exactly what I am looking for.

Sean


On 3/26/07, Brent Brown <.....brent.brownKILLspamspam.....clear.net.nz> wrote:
{Quote hidden}

> -

2007\03\26@225720 by Sean Breheny

face picon face
Hi John,

Thanks for your reply. I was trying to do this without the cost of an
isolated DC to DC converter (especially considering that only
microamps are needed to keep the FET gates charged).

Sean

On 3/26/07, John Dammeyer <johndspamspam_OUTautoartisans.com> wrote:
{Quote hidden}

> > {Original Message removed}

2007\03\26@230512 by Sean Breheny

face picon face
Hi Robert,

Thanks for your reply. Please see my responses below.

On 3/26/07, Robert Rolf <@spam@Robert.RolfKILLspamspamualberta.ca> wrote:
> Why not break your FETs into multiple banks and drive then with a
> multiple phase low off duty cycle signal?
> You could then use bootstrap drive mode. (clamp diode to give fast
> recharge recovery)
> If you have 8 Fets, you'd have 1 of 8 off for a few milliseconds
> every second so at most you'd need 1 extra Fet to cover the load
> of the one that is off.l

That's not all that bad an idea but I had a feeling that there was a
simpler way to do this which was a standard "easy way" to do this kind
of thing. Brent seems to have such an answer.

> Huh? The spec sheet says it does DC.
>
> "To ensure static DC operation an integrated recharge path charges the
> bootstrap cap while the driver is switched off."
>

That's what I thought, too. However, read further and you will see
that they are never clear about how that would work. There is no
charge pump or other boosting supply present. Also, they talk about
the bootstrap cap being charged "when the driver is off", which sounds
suspiciously like a normal bootstrap driver. The "recharge path" they
show would only help when the driver was in fact off. It shows no way
of charging while the FET is on. My tests confirmed this - after turn
on the gate drive slowly fell off until the source was lower than the
gate drive bias supply.

I think it must be poorly translated or misunderstood by the datasheet
writer. I think what they actually mean is that it is like a normal
bootstrapped driver except that they provide an internal path to
recharge the cap so you do not need a low-side switch (which would
normally ground the source node and charge the cap).

> And you can't use a relay because???
> Or bridge the Fets with a relay after their initial operation?

We looked at relays and couldn't find anything which could break 80VDC
and also carry 100A while closed for anything less than $90 USD in
large quantity. Most power relays are only spec'd to 32VDC.

Sean


>
> Robert
>
> -

2007\03\26@230700 by Sean Breheny

face picon face
Hi Jake,

I don't have the model numbers off-hand but take a look at some of the
ones produced by Intersil and Linear Technologies. This does seem to
be a standard thing for hot-swappable devices on computers, etc.

Sean

On 3/26/07, Jake Anderson <KILLspamjakeKILLspamspamvapourforge.com> wrote:
> no but I would be interested in which ones you found for < 80v if you
> happen to have them handy?
> -

2007\03\26@230733 by Sean Breheny

face picon face
Hi Nate,

Thanks. I think I'm going to try Brent's idea.

Sean


On 3/26/07, Nate Duehr <RemoveMEnateTakeThisOuTspamnatetech.com> wrote:
{Quote hidden}

> -

2007\03\26@231802 by Sean Breheny

face picon face
Hi Peter,

I'm sure something like this would work but I'm going to try the
integrated solution which Brent suggested first. Thanks!

Sean

On 3/26/07, peter green <TakeThisOuTplugwashEraseMEspamspam_OUTp10link.net> wrote:

{Quote hidden}

> -

2007\03\26@233327 by Herbert Graf

flavicon
face
On Mon, 2007-03-26 at 19:56 -0400, Sean Breheny wrote:
> Hi all,
>
> I have a circuit which needs to switch a 48V supply (which can rise as
> high as 80V). The load is ground referenced and can draw as much as
> 100 Amps. The switch, however, need not open while any more than 1 Amp
> is flowing.

Have you considered using a relay? This it the typical type of
application for a relay, unless speed or power consumption is really
important.

TTYL

2007\03\26@234143 by Richard Prosser

picon face
> We looked at relays and couldn't find anything which could break 80VDC
> and also carry 100A while closed for anything less than $90 USD in
> large quantity. Most power relays are only spec'd to 32VDC.
>
> Sean
>
>
> >
> > Robert
> >

Robert,
Check Allbright, Prestolite, AMTEK (spelling?). Also there are some
Chinese contactors (Guizhou Tianyi Electrical) that may meet your
price range.

We use contactors up to about 1200A at similar voltages. 100A is at
the small end of things!

RP

2007\03\27@041516 by Peter P.

picon face
Sean Breheny <shb7 <at> cornell.edu> writes:

> > http://www.irf.com/technical-info/appnotes/an-1017.pdf

Imho this is a great part but simulating the circuit first could be important.
When I had to do such a floating switch I used a Royer style dc/dc converter and
a hysteresis element after the high side rectifier. Imho the control current
supplied by the irf part is insufficient for a stable gate drive when noise etc
is present and during switching. Perhaps it could be used to supply power to a
standard gate driver instead of being used stand-alone.

Peter P.


2007\03\27@042811 by Alan B. Pearce

face picon face
>Anyone know of an IC to do gate drive for something like this?

I take it that you are not PWM driving this seeing you say it will be on for
days.

In that case I would use a small isolated dc-dc converter to get a drive
voltage above the supply voltage, and make a gate drive circuit out of
discrete devices, as you are not looking for real high speed switching.

2007\03\27@043441 by Alan B. Pearce

face picon face
>> The following are an absolutley brilliant invention and not well
>> enough known (IMHO)...
>>
>> www.irf.com/product-info/datasheets/data/pvin.pdf
>>
>
>P.S. For more information check out their application note...
>
> http://www.irf.com/technical-info/appnotes/an-1017.pdf

hey guys, that is an absolutely brilliant solution to a problem I have been
looking at. Must investigate the pricing of these ...



2007\03\27@091450 by Sean Breheny

face picon face
Hi Richard,

That was I who made the comment about not finding inexpensive relays,
not Robert. I should have removed his name when I edited the quoted
text.

To really justify going to a relay, I'd say it would have to be less
than $20 in high quantity. $90 is not my requirement, simply the
cheapest I found.

Sean

On 3/26/07, Richard Prosser <RemoveMErhprosserspamTakeThisOuTgmail.com> wrote:
{Quote hidden}

> -

2007\03\31@140229 by Sean Breheny

face picon face
Hi all,

Thanks again for the help. I got some of the PVI1050N chips which
Brent mentioned. They work great and look like an ideal solution for
me. I don't care about turn-on time, only turn off time. I was able to
speed that up by adding a BJT and a diode so that the PVI charges the
FET gate through the diode and pulls it low using the transistor. This
gave me 2ms turn-on time and 5us turn off time for 30nF gate
capacitance (three FETs in parallel).

Sean


On 3/27/07, Sean Breheny <shb7EraseMEspam.....cornell.edu> wrote:
{Quote hidden}

More... (looser matching)
- Last day of these posts
- In 2007 , 2008 only
- Today
- New search...