Logic level HV fet...

Mike Deblis · Jan 27, 2005

Hi,

I'm looking for a 200 - 250V FET with low Qg, low RDSon (only needs maybe 3A
peak Ids, but low RDSon for efficiency) and LOGIC LEVEL GATE for use in an
SMPS that only has a 9V supply - the SMPS is in boost configuration to give
180V @ 20mA out, probably going to use the LTC1872 if I can.

Any ideas would be appreciated - I've not had a lot of luck so far - I know
its a tall order. An SMD footprint would also be good.

Thanks

Mike

Genome · Jan 27, 2005

"Mike Deblis" <mdeblis@hotmail.com> wrote in message
news:35ru47F4mkh6eU1@individual.net...

Hi,

I'm looking for a 200 - 250V FET with low Qg, low RDSon (only needs maybe
3A
peak Ids, but low RDSon for efficiency) and LOGIC LEVEL GATE for use in an
SMPS that only has a 9V supply - the SMPS is in boost configuration to
give
180V @ 20mA out, probably going to use the LTC1872 if I can.

Any ideas would be appreciated - I've not had a lot of luck so far - I
know
its a tall order. An SMD footprint would also be good.

Thanks

Mike

Use a voltage boosted boost converter. You tap the inductor so that the FET
sees a fraction of the output voltage.

----nnnnnnnnnnnn----->|-----
|
|
|--
|<-
|--
|
|
-------------------------------

DNA

Fritz Schlunder · Jan 27, 2005

"Mike Deblis" <mdeblis@hotmail.com> wrote in message
news:35ru47F4mkh6eU1@individual.net...

Hi,

I'm looking for a 200 - 250V FET with low Qg, low RDSon (only needs maybe
3A
peak Ids, but low RDSon for efficiency) and LOGIC LEVEL GATE for use in an
SMPS that only has a 9V supply - the SMPS is in boost configuration to
give
180V @ 20mA out, probably going to use the LTC1872 if I can.

Any ideas would be appreciated - I've not had a lot of luck so far - I
know
its a tall order. An SMD footprint would also be good.

Thanks

Mike

Hi there. Unfortunately the pickings for 200V or more logic level MOSFETs
is exceedingly slim. For the most part your only potentially feasible
choices I'm aware of are the IRL620, IRL630, IRL640 (TO-220 devices) and the
D2Pak versions of those same parts: IRL620S, IRL630S, IRL640S. Here is the
datasheet for the IRL630S which is a 200V 0.4 ohm Rds(on) D2Pak part.

http://www.irf.com/product-info/datasheets/data/irl630s.pdf

Digikey sells all of these device types. They aren't really very good,
noticeably inferior to their standard gate drive newer cousins.

The LTC1872 is a nice part, but the switching frequency is really
unreasonable for this application. Efficiency would be hideous at 550kHz
operation, no matter your MOSFET selection. Without doing any major
calculations before spouting off conclusions, I would bet efficiency would
be so low as to preclude the use of an SMD MOSFET for thermal reasons alone,
despite your low 3.6W output power. In addition to abysmal efficiency, you
could also expect tremendous EMI production, likely way beyond FCC
limitations. If you listen to the radio at all, you quite possibly might
find that all but the most powerful AM and FM band stations will have become
too static filled to listen to.

The problem is high dV/dt radiates. A little 3.3V to 5V step up converter
can operate at high switching frequency with very fast transitions without
producing very much EMI. The drain of the MOSFET would only swing from
0-5V. With 180V output the swing suddenly becomes 0-180V. Unless the
switching speed is reduced drastically, the dV/dt will be greatly higher and
hence much stronger EMI radiated. At first it may seem strange that a
switcher operating at 550kHz could interfere with the FM band which operates
around 100MHz. It is important to remember that a 550kHz squarewave with
fast edges contains large amounts of higher frequency content.

I would strongly recommend using something much closer to 20kHz as your
switching frequency. Make sure to use discontinuous conduction mode since
the control loop gain gets really large (IE: impossible to make stable) for
large step up ratios (which 9V to 180V certainly qualifies) in continuous
conduction mode. With a 20kHz switching frequency and 9V input an inductor
value of vaguely around 150uH would seem to be reasonable.

Fred Bloggs · Jan 27, 2005

Genome wrote:

"Mike Deblis" <mdeblis@hotmail.com> wrote in message
news:35ru47F4mkh6eU1@individual.net...

Hi,

I'm looking for a 200 - 250V FET with low Qg, low RDSon (only needs maybe

3A

peak Ids, but low RDSon for efficiency) and LOGIC LEVEL GATE for use in an
SMPS that only has a 9V supply - the SMPS is in boost configuration to

give

180V @ 20mA out, probably going to use the LTC1872 if I can.

Any ideas would be appreciated - I've not had a lot of luck so far - I

know

its a tall order. An SMD footprint would also be good.

Thanks

Mike

Use a voltage boosted boost converter. You tap the inductor so that the FET
sees a fraction of the output voltage.

----nnnnnnnnnnnn----->|-----
|
|
|--
|<-
|--
|
|
-------------------------------

DNA

Although diode sees a multiple of reverse output voltage, the duty D can
be significantly reduced from the 95% required of single inductor 20:1
multiplication of 9V->180V. Good idea.

Harry Dellamano · Jan 27, 2005

"Fritz Schlunder" <me@privacy.net> wrote in message
news:35s6nvF4se566U1@individual.net...

The LTC1872 is a nice part, but the switching frequency is really
unreasonable for this application. Efficiency would be hideous at 550kHz
operation, no matter your MOSFET selection. Without doing any major
calculations before spouting off conclusions, I would bet efficiency would
be so low as to preclude the use of an SMD MOSFET for thermal reasons
alone,
despite your low 3.6W output power. In addition to abysmal efficiency,
you
could also expect tremendous EMI production, likely way beyond FCC
limitations. If you listen to the radio at all, you quite possibly might
find that all but the most powerful AM and FM band stations will have
become
too static filled to listen to.

The problem is high dV/dt radiates. A little 3.3V to 5V step up converter
can operate at high switching frequency with very fast transitions without
producing very much EMI. The drain of the MOSFET would only swing from
0-5V. With 180V output the swing suddenly becomes 0-180V. Unless the
switching speed is reduced drastically, the dV/dt will be greatly higher
and
hence much stronger EMI radiated. At first it may seem strange that a
switcher operating at 550kHz could interfere with the FM band which
operates
around 100MHz. It is important to remember that a 550kHz squarewave with
fast edges contains large amounts of higher frequency content.

I would strongly recommend using something much closer to 20kHz as your
switching frequency. Make sure to use discontinuous conduction mode since
the control loop gain gets really large (IE: impossible to make stable)
for
large step up ratios (which 9V to 180V certainly qualifies) in continuous
conduction mode. With a 20kHz switching frequency and 9V input an
inductor
value of vaguely around 150uH would seem to be reasonable.

Hi Fritz,
This is a great application for running a simple boost in Zero Voltage
Switching mode. Add more capacity in parallel with the FET to control
(resonate) rise and fall times to about 200nS. Operate the PWM in constant
"off time" and current controlled "on time". Most control IC can be
configured for this. I use this mode of operation so I can lisiten to the
radio as I check it out. Piece of cake.
Harry

>

John Larkin · Jan 27, 2005

On Thu, 27 Jan 2005 10:29:28 -0000, "Mike Deblis"
<mdeblis@hotmail.com> wrote:

Hi,

I'm looking for a 200 - 250V FET with low Qg, low RDSon (only needs maybe 3A
peak Ids, but low RDSon for efficiency) and LOGIC LEVEL GATE for use in an
SMPS that only has a 9V supply - the SMPS is in boost configuration to give
180V @ 20mA out, probably going to use the LTC1872 if I can.

Any ideas would be appreciated - I've not had a lot of luck so far - I know
its a tall order. An SMD footprint would also be good.

Thanks

Mike

9 volts is plenty of gate drive for most regular mosfets. Drain
current will be well below 1 amp, no big deal.

John

john jardine · Jan 27, 2005

"Mike Deblis" <mdeblis@hotmail.com> wrote in message
news:35ru47F4mkh6eU1@individual.net...

Hi,

I'm looking for a 200 - 250V FET with low Qg, low RDSon (only needs maybe
3A
peak Ids, but low RDSon for efficiency) and LOGIC LEVEL GATE for use in an
SMPS that only has a 9V supply - the SMPS is in boost configuration to
give
180V @ 20mA out, probably going to use the LTC1872 if I can.

Any ideas would be appreciated - I've not had a lot of luck so far - I
know
its a tall order. An SMD footprint would also be good.

Thanks

Mike

The 2SK2350 is 200V, 0.26ohms, with 4V gate drive.

legg · Jan 28, 2005

On Thu, 27 Jan 2005 10:29:28 -0000, "Mike Deblis"
<mdeblis@hotmail.com> wrote:

Hi,

I'm looking for a 200 - 250V FET with low Qg, low RDSon (only needs maybe 3A
peak Ids, but low RDSon for efficiency) and LOGIC LEVEL GATE for use in an
SMPS that only has a 9V supply - the SMPS is in boost configuration to give
180V @ 20mA out, probably going to use the LTC1872 if I can.

Any ideas would be appreciated - I've not had a lot of luck so far - I know
its a tall order. An SMD footprint would also be good.

Siliconix Si4490DY Nchannel 200V 0R09 in SO8, is characterized with

6Vds.

http://www.vishay.com/doc?71341

RL

Fritz Schlunder · Jan 28, 2005

"legg" <legg@nospam.magma.ca> wrote in message
news:944jv0h42j87qd6rejrfqa7lm2qqoeb0iv@4ax.com...

On Thu, 27 Jan 2005 10:29:28 -0000, "Mike Deblis"
mdeblis@hotmail.com> wrote:

Hi,

I'm looking for a 200 - 250V FET with low Qg, low RDSon (only needs maybe
3A
peak Ids, but low RDSon for efficiency) and LOGIC LEVEL GATE for use in
an
SMPS that only has a 9V supply - the SMPS is in boost configuration to
give
180V @ 20mA out, probably going to use the LTC1872 if I can.

Any ideas would be appreciated - I've not had a lot of luck so far - I
know
its a tall order. An SMD footprint would also be good.

Siliconix Si4490DY Nchannel 200V 0R09 in SO8, is characterized with
6Vds.

http://www.vishay.com/doc?71341

RL

Hey now that is an interesting part. I wonder how much it costs...

Fritz Schlunder · Jan 28, 2005

"Harry Dellamano" <harryd@tdsystems.org> wrote in message
news:mJ7Kd.975$lg5.564@trnddc06...

Hi Fritz,
This is a great application for running a simple boost in Zero Voltage
Switching mode. Add more capacity in parallel with the FET to control
(resonate) rise and fall times to about 200nS. Operate the PWM in constant
"off time" and current controlled "on time". Most control IC can be
configured for this. I use this mode of operation so I can lisiten to the
radio as I check it out. Piece of cake.
Harry

I agree, ZVS would be very nice for this application. This is a good idea.

mike · Jan 28, 2005

Genome wrote:
snipped all the bigoted stuff

Why'd you have to go ruin a perfectly good suggestion with all that
crap.

Of course, you have to do the math for all the options. But you can at
least be objective about it.

mike

--
Return address is VALID.
Wanted, PCMCIA SCSI Card for HP m820 CDRW.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
http://nm7u.tripod.com/homepage/te.html
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Bunch of stuff For Sale and Wanted at the link below.
http://www.geocities.com/SiliconValley/Monitor/4710/

Winfield Hill · Jan 28, 2005

legg wrote...

Fritz Schlunder wrote:
legg wrote...
Mike Deblis wrote:

I'm looking for a 200 - 250V FET with low Qg, low RDSon (only needs
maybe 3A peak Ids, but low RDSon for efficiency) and LOGIC LEVEL
GATE for use in an SMPS that only has a 9V supply ...

Siliconix Si4490DY Nchannel 200V 0R09 in SO8, is characterized with
6Vds. http://www.vishay.com/doc?71341

Hey now that is an interesting part. I wonder how much it costs...

Never inquired about Si4490. The 150V parts were 0R05 or less.

It's a boring part. Yawn.

--
Thanks,
- Win

Winfield Hill · Jan 28, 2005

john jardine wrote...

Mike Deblis wrote:

I'm looking for a 200 - 250V FET with low Qg, low RDSon (only
needs maybe 3A peak Ids, but low RDSon for efficiency) and
LOGIC LEVEL GATE for use in an SMPS that only has a 9V supply ...

The 2SK2350 is 200V, 0.26ohms, with 4V gate drive.

It appears the 0.26ohm rating is with 10V drive.
That's a boring part. Nothing special. Yawn.

--
Thanks,
- Win

legg · Jan 28, 2005

On 28 Jan 2005 04:24:20 -0800, Winfield Hill
<hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

legg wrote...

Fritz Schlunder wrote:
legg wrote...
Mike Deblis wrote:

I'm looking for a 200 - 250V FET with low Qg, low RDSon (only needs
maybe 3A peak Ids, but low RDSon for efficiency) and LOGIC LEVEL
GATE for use in an SMPS that only has a 9V supply ...

Siliconix Si4490DY Nchannel 200V 0R09 in SO8, is characterized with
6Vds. http://www.vishay.com/doc?71341

Hey now that is an interesting part. I wonder how much it costs...

Never inquired about Si4490. The 150V parts were 0R05 or less.

It's a boring part. Yawn.

Reality is such a bore!

Shall I peel you a grape?

RL

Rich Grise · Jan 28, 2005

On Fri, 28 Jan 2005 01:21:27 -0800, mike wrote:

Genome wrote:
snipped all the bigoted stuff

Why'd you have to go ruin a perfectly good suggestion with all that
crap.

Of course, you have to do the math for all the options. But you can at
least be objective about it.

Oh, I've plonked Genome some time ago for gratuitous vulgarity.

Thanks for the reminder!
Rich

Joerg · Jan 28, 2005

Hello John,

Look at the graphs. This fet has very nearly the same Ron at a 5V gate. This
is in sharp contrast to many Fets advertised as being 'logic-level' when in
actual fact they are barely starting to move, hence incapable of doing any
real work at this drive level.

If you look at the Vgs versus Vds graph in the middle of page 3 there is
less than a volt of head room at 5V gate drive before Vds shoots up and
potentially turns the device into a pile of ash. Too close for comfort
to me.

Go on then, suggest a logic level fet, easily available at a reasonable
price, that should be preferred for this switching job. An insulated case
type would be nice. .

That's just the problem, not much out there. It is an issue I run into a
lot and often end up with bipolar transistors. What really drives me up
the wall is a glitzy ad for some new FET, saying it is guaranteed 3V or
something and then in the fine print I find that was for 1mA and Vds=1V.
At least one can then crumple the data sheet, form a ball and smack it
into the bin across the room. Or use it to light the wood stove.

Regards, Joerg

http://www.analogconsultants.com

Genome · Jan 28, 2005

"mike" <spamme0@netscape.net> wrote in message
news:41FA0417.1010100@netscape.net...

Genome wrote:
snipped all the bigoted stuff

Why'd you have to go ruin a perfectly good suggestion with all that
crap.

Of course, you have to do the math for all the options. But you can at
least be objective about it.

mike

--

OK, objectively speaking, Mel Brooks might have been worth it.

DNA

Genome · Jan 29, 2005

"Rich Grise" <richgrise@example.net> wrote in message
news

an.2005.01.28.20.35.55.45022@example.net...

On Fri, 28 Jan 2005 01:21:27 -0800, mike wrote:

Genome wrote:
snipped all the bigoted stuff

Why'd you have to go ruin a perfectly good suggestion with all that
crap.

Of course, you have to do the math for all the options. But you can at
least be objective about it.

Oh, I've plonked Genome some time ago for gratuitous vulgarity.

Thanks for the reminder!
Rich

Ta muchly for plonking me.

Your services are much apprecieated.

DNA

Jim Thompson · Jan 29, 2005

On Sat, 29 Jan 2005 01:19:07 GMT, "Genome" <ilike_spam@yahoo.co.uk>
wrote:

"Rich Grise" <richgrise@example.net> wrote in message
newsan.2005.01.28.20.35.55.45022@example.net...
[snip]

Oh, I've plonked Genome some time ago for gratuitous vulgarity.

Thanks for the reminder!
Rich

Ta muchly for plonking me.

Your services are much apprecieated.

DNA

480)460-2350 | |
| E-mail Address at Website Fax

Winfield Hill · Jan 29, 2005

legg wrote...

Shall I peel you a grape?

No, I prefer it with the skin.

--
Thanks,
- Win

Logic level HV fet...

Mike Deblis

Guest

Genome

Guest

Fritz Schlunder

Guest

Fred Bloggs

Guest

Harry Dellamano

Guest

John Larkin

Guest

john jardine

Guest

legg

Guest

Fritz Schlunder

Guest

Fritz Schlunder

Guest

mike

Guest

Winfield Hill

Guest

Winfield Hill

Guest

legg

Guest

Rich Grise

Guest

Joerg

Guest

Genome

Guest

Genome

Guest

Jim Thompson

Guest

Winfield Hill

Guest

Log in

Welcome to EDABoard.com

Sponsor