| Author |
Message |
Mike Deblis
Guest
|
 Posted:
Thu Jan 27, 2005 4:29 pm Post subject:
Logic level HV fet... |
|
|
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
|
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PeteS
Guest
|
| Posted:
Thu Jan 27, 2005 5:49 pm Post subject:
Re: Logic level HV fet... |
|
|
At voltages such as this, Qg (and Ciss, Coss) are more important than
Rds(on) although obviously it has to be reasonably low. The reason is
the large voltage swing of the source when the Switch turns on. It will
go from Vout to Vin, and capacitively couple that delta to other parts
of the SMPS with possibly harrowing results. At the load level you
suggest, a device in the hundreds of milliohm range would probably be
suitable (but check the SOA curve).
Most FETs at this breakdown are normally specified at 10V Vgs. If 9V is
not sufficient, you can always make a simple capacitive charge pump to
run the boost driver (Linear tech has excellent app notes on this sort
of thing).
For a typical device list, see this page
http://ec.irf.com/v6/en/US/adirect/ir?cmd=catNavigateFrame&punchInID=54
which lists the excellent range of IR HexFets(tm). Similar devices and
capabilities are also available from Vishay-Siliconix and Fairchild
(although the selection from fairchild is more limited).
As for footprints, many high voltage devices come in D-PAK or D2-PAK
surface mount footprints, to name the more common ones.
Cheers
PeteS
Mike Deblis wrote:
| Quote: | 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 |
|
|
| Back to top |
|
|
Genome
Guest
|
| Posted:
Thu Jan 27, 2005 6:49 pm Post subject:
Re: Logic level HV fet... |
|
|
"Mike Deblis" <mdeblis@hotmail.com> wrote in message
news:35ru47F4mkh6eU1@individual.net...
| Quote: | 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
|
|
| Back to top |
|
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Fritz Schlunder
Guest
|
| Posted:
Thu Jan 27, 2005 6:59 pm Post subject:
Re: Logic level HV fet... |
|
|
"Mike Deblis" <mdeblis@hotmail.com> wrote in message
news:35ru47F4mkh6eU1@individual.net...
| Quote: | 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. |
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|
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Mike Deblis
Guest
|
| Posted:
Thu Jan 27, 2005 7:09 pm Post subject:
Re: Logic level HV fet... |
|
|
"Fritz Schlunder" <me@privacy.net> wrote in message
news:35s6nvF4se566U1@individual.net...
| Quote: | 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.
....
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,
Thanks for the reply. Normally, I use a MAX1771 which runs at 50kHz and
gives me about 87% efficiency in this configuration - really a very nice
chip.
However, getting the MAX chips in Europe and elsewhere is often a pain, and
I was looking at emulating its performance using LTspice when an LT FAE
mentioned their devices, which are emulated for you in LTspice, and he
suggested I look at those as well, hence this investigation.
I agree with everything you say about the LT chip - it is a very nice device
in a very small package, but the maximum efficiency I've been able to get is
in the order of 65%.... Also, unlike the MAX1771, the LT device can only
handle up to 9.8V in, which really means logic level FETs - if I was going
at add a charge pump or whatever for the gate drive, I might as well use the
MAX device which is more forgiving anyway...
Ho, hum... just a thought...
Thanks
Mike |
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|
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Fred Bloggs
Guest
|
| Posted:
Thu Jan 27, 2005 7:31 pm Post subject:
Re: Logic level HV fet... |
|
|
Genome wrote:
| Quote: | "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. |
|
| Back to top |
|
|
Genome
Guest
|
| Posted:
Thu Jan 27, 2005 7:38 pm Post subject:
Re: Logic level HV fet... |
|
|
"Fred Bloggs" <nospam@nospam.com> wrote in message
news:41F8ED17.3080900@nospam.com...
| Quote: |
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,
|
Yes, that's the caveat.
DNA
the duty D can
| Quote: | be significantly reduced from the 95% required of single inductor 20:1
multiplication of 9V->180V. Good idea.
|
|
|
| Back to top |
|
|
Harry Dellamano
Guest
|
| Posted:
Thu Jan 27, 2005 9:25 pm Post subject:
Re: Logic level HV fet... |
|
|
"Fritz Schlunder" <me@privacy.net> wrote in message
news:35s6nvF4se566U1@individual.net...
| Quote: |
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
> |
|
| Back to top |
|
|
John Larkin
Guest
|
| Posted:
Thu Jan 27, 2005 10:02 pm Post subject:
Re: Logic level HV fet... |
|
|
On Thu, 27 Jan 2005 10:29:28 -0000, "Mike Deblis"
<mdeblis@hotmail.com> wrote:
| Quote: | 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 |
|
| Back to top |
|
|
john jardine
Guest
|
| Posted:
Fri Jan 28, 2005 6:09 am Post subject:
Re: Logic level HV fet... |
|
|
"Mike Deblis" <mdeblis@hotmail.com> wrote in message
news:35ru47F4mkh6eU1@individual.net...
| Quote: | 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. |
|
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| Back to top |
|
|
legg
Guest
|
| Posted:
Fri Jan 28, 2005 7:11 am Post subject:
Re: Logic level HV fet... |
|
|
On Thu, 27 Jan 2005 10:29:28 -0000, "Mike Deblis"
<mdeblis@hotmail.com> wrote:
| Quote: | 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 |
|
| Back to top |
|
|
mike
Guest
|
| Posted:
Fri Jan 28, 2005 7:50 am Post subject:
Re: Logic level HV fet... |
|
|
Genome wrote:
| Quote: | "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
|
Once you've decided to tap the inductor, is there any practical
difference between that and a transformer. Probably still want
different size wire in the two sections anyway.
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/ |
|
| Back to top |
|
|
John Popelish
Guest
|
| Posted:
Fri Jan 28, 2005 8:17 am Post subject:
Re: Logic level HV fet... |
|
|
mike wrote:
| Quote: |
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
Once you've decided to tap the inductor, is there any practical
difference between that and a transformer. Probably still want
different size wire in the two sections anyway.
mike
|
I agree. Once you have decided to spring for a custom magnetic part,
you have all sorts of choices that trade cost and complexity in one
place for cost, efficiency and simplicity in others. I would consider
a 3 winding transformer, with the primary rectified and both
secondaries separately rectified, and all 3 stacked in series, so that
the transistor would see only about 60 volts and schottky rectifiers
could be used all 3 places. 100 volt fets are more common than 200
volt units in SMT low gate voltage versions.
--
John Popelish |
|
| Back to top |
|
|
Fritz Schlunder
Guest
|
| Posted:
Fri Jan 28, 2005 10:01 am Post subject:
Re: Logic level HV fet... |
|
|
"legg" <legg@nospam.magma.ca> wrote in message
news:944jv0h42j87qd6rejrfqa7lm2qqoeb0iv@4ax.com...
| Quote: | 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... |
|
| Back to top |
|
|
Fritz Schlunder
Guest
|
| Posted:
Fri Jan 28, 2005 10:02 am Post subject:
Re: Logic level HV fet... |
|
|
"Harry Dellamano" <harryd@tdsystems.org> wrote in message
news:mJ7Kd.975$lg5.564@trnddc06...
| Quote: | 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. |
|
| Back to top |
|
|
|
|
|
|
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