Any logic-level FETs with breakdown 300V+?

[Joerg]

Hello,

Just curious, although I am not holding my breath that any exist:

Are there FETs with a Vds rating of 300V or higher, preferably DPAK
(TO-252), that have a guaranteed Rdson of around 1ohm or less at Vgs of
6V or less? 1A current or higher.

With guaranteed I mean not in some graph but with an entry under "max"
in the tables. The usual ones are only rated at 10V although the figures
indicate that they could have rated them for lower gate drive voltages
at lesser current. But the manufacturers chose not to and trying to get
any endorsement to that effect is like kicking a big oak tree.

The motivation is the usual. Logic drive, the typical MIC4422 or similar
is too much money plus it would need its personal supply voltage which
would have to be made.

 

[Jamie]

Hello,

Just curious, although I am not holding my breath that any exist:

Are there FETs with a Vds rating of 300V or higher, preferably DPAK
(TO-252), that have a guaranteed Rdson of around 1ohm or less at Vgs of
6V or less? 1A current or higher.

With guaranteed I mean not in some graph but with an entry under "max"
in the tables. The usual ones are only rated at 10V although the figures
indicate that they could have rated them for lower gate drive voltages
at lesser current. But the manufacturers chose not to and trying to get
any endorsement to that effect is like kicking a big oak tree.

The motivation is the usual. Logic drive, the typical MIC4422 or similar
is too much money plus it would need its personal supply voltage which
would have to be made.

http://www.datasheetcatalog.com/datasheets_pdf/S/T/B/2/STB20NK50ZT4.shtml

how about that ?

http://webpages.charter.net/jamie_5"

 

[JSprocket]

Are there FETs with a Vds rating of 300V or higher, preferably DPAK
(TO-252), that have a guaranteed Rdson of around 1ohm or less at Vgs of
6V or less? 1A current or higher.

I've no idea, but seeing what will happen to the rest of the system if
one fails d-g, I'd be tempted to opto isolate it. I've seen PCBs with a
big, brown- edged hole where the electronics used to be.

 

[TheM]

http://www.datasheetcatalog.com/datasheets_pdf/S/T/B/2/STB20NK50ZT4.shtml

how about that ?

Pretty nice. Now does digikey stock them?

M

 

[Spehro Pefhany]

Hello,

Just curious, although I am not holding my breath that any exist:

Are there FETs with a Vds rating of 300V or higher, preferably DPAK
(TO-252), that have a guaranteed Rdson of around 1ohm or less at Vgs of
6V or less? 1A current or higher.

With guaranteed I mean not in some graph but with an entry under "max"
in the tables. The usual ones are only rated at 10V although the figures
indicate that they could have rated them for lower gate drive voltages
at lesser current. But the manufacturers chose not to and trying to get
any endorsement to that effect is like kicking a big oak tree.

The motivation is the usual. Logic drive, the typical MIC4422 or similar
is too much money plus it would need its personal supply voltage which
would have to be made.

Have not noticed any (though there are a few 200V small MOSFETs rated
for logic-level drive, but higher Rds(on) and lower current rating
than you want.

OTOH, you'll have thousands of inexpensive jellybean choices if you
make it 10V drive.


Best regards,
Spehro Pefhany

 

[Joerg]

Bipolar? Darlington?

Way too slow. Most have turn-off times in the usec range. Sure, you can
hold them a wee bit above saturation but then circuit complexity begins
to eat real estate and pennies.

 

[Joerg]

http://www.datasheetcatalog.com/datasheets_pdf/S/T/B/2/STB20NK50ZT4.shtml

how about that ?

Like usual, Rdson max only guaranteed at 10V and the transfer
characteristic looks rather spooky. It's most likely going to explode if
you try to switch heavy loads at 5V:

http://www.st.com/stonline/products/literature/ds/9118/stb20nk50z.pdf

 

[Joerg]

I've no idea, but seeing what will happen to the rest of the system if
one fails d-g, I'd be tempted to opto isolate it. I've seen PCBs with a
big, brown- edged hole where the electronics used to be.

We are fuse-protected

 

[Joerg]

Have not noticed any (though there are a few 200V small MOSFETs rated
for logic-level drive, but higher Rds(on) and lower current rating
than you want.

OTOH, you'll have thousands of inexpensive jellybean choices if you
make it 10V drive.

Yeah, which is what we'll do. I was just hoping. 10V drive will add a
lot of stuff and we are really cramped for space on this one.

I wish there were fast BJT under 15c with hold-off Schottky built in. Is
there still time to write to Santa ...?

 

[Joerg]

Silly me, I should have know that speed was important here.

Sorry, should have mentioned that.

 

[Joerg]

Does the drive need to be truly DC-coupled? You could maybe do some
cute stuff if the fet doesn't have to be on for a long time.

I could but then the transformed-up Cgs would hit us from behind. Looks
like we might have to provide a clean and staunch 10V.

 

[Nico Coesel]

Yeah, which is what we'll do. I was just hoping. 10V drive will add a
lot of stuff and we are really cramped for space on this one.

A two-stage solution (N channel pulling a P channel to ground) is out
of the question?

 

[Joerg]

A two-stage solution (N channel pulling a P channel to ground) is out
of the question?

Requires dead-time control (+8 parts) or we'll run a chance of sitting
there at the EMC lab with egg in our faces.

 

[Jamie]

Pretty nice. Now does digikey stock them?

M

Mouser has them.


http://webpages.charter.net/jamie_5"

 

[Jamie]

Like usual, Rdson max only guaranteed at 10V and the transfer
characteristic looks rather spooky. It's most likely going to explode if
you try to switch heavy loads at 5V:

http://www.st.com/stonline/products/literature/ds/9118/stb20nk50z.pdf

And why can't you use a charge pump inverter source on the driving side
for the gate?
I've done that before using simple things like a PNP for high side to
drive the gate via a charge pump inverter and common on the low side via
a open collector NPN drive.

It works perfectly, since the charge pump reservoir cap has more than
enough to over come the Cgs on the gate for the initial transition. You
may also consider a low value R in series with gate to avoid parasitic
noise, like ringing for example. Many times board design can over come
this how ever, it does not hurt to through in a 1..10 R.

Or, just use a ready made gate driver chip with the same characteristics.

http://webpages.charter.net/jamie_5"

 

[Eeyore]

http://www.datasheetcatalog.com/datasheets_pdf/S/T/B/2/STB20NK50ZT4.shtml

how about that ?

USELESS.

VGS(th) Gate Threshold Voltage VDS = VGS, ID = 100 uA 3V min 3.75V typ 4.5 V
max

Do you suggest Joerg selects them ?

Graham

 

[Jamie]

Jamie wrote:




USELESS.

VGS(th) Gate Threshold Voltage VDS = VGS, ID = 100 uA 3V min 3.75V typ 4.5 V
max

Do you suggest Joerg selects them ?

Graham

Jesus christ..
You got to be kidding me.

That fits every spec he was looking for with the exception of
the gate voltage for which, is the simplest thing to work around. Which
is why they make charge pump drivers in cases like this..

Yes, it adds a little extra to the component count how ever, this has
been answered many times with various types of gate drivers.

This is 101 design techniques around FETS. Gate voltage in most
cases is the smallest issues.



http://webpages.charter.net/jamie_5"

 

[Eeyore]

That fits every spec he was looking for with the exception of
the gate voltage.

He specifically asked for LOGIC LEVEL !

Graham

 

[Joerg]

And why can't you use a charge pump inverter source on the driving side
for the gate?
I've done that before using simple things like a PNP for high side to
drive the gate via a charge pump inverter and common on the low side via
a open collector NPN drive.

It works perfectly, since the charge pump reservoir cap has more than
enough to over come the Cgs on the gate for the initial transition. You
may also consider a low value R in series with gate to avoid parasitic
noise, like ringing for example. Many times board design can over come
this how ever, it does not hurt to through in a 1..10 R.

Well, there ain't so much space left as for a carpenter ant to squish in
there ;-)

Or, just use a ready made gate driver chip with the same characteristics.

Needs a separate supply and thus even more space. But if all else fails
that's what we'll have to do. On another design a month ago I did that
but there I had over 200 square inches of free land. So I just stuck a
claim somewhere ...

 

[Jamie]

Well, there ain't so much space left as for a carpenter ant to squish in
there ;-)



Needs a separate supply and thus even more space. But if all else fails
that's what we'll have to do. On another design a month ago I did that
but there I had over 200 square inches of free land. So I just stuck a
claim somewhere ...

Making a low yield supply on board to drive a fet should be a trivial
task, one that requires very little real-estate.
The size of gate driver chips are very small these days. One could even
plant a mini daughter board just in front/over the top of the FET if
space is tight.

Did that the other day btw, to modify a circuit that was already in
use.! Needed to enhance a analog PID board, so I etched out a mini .5"
square DS board and elevated it over the main board with the
connection legs...

In your case, I guess if you wanted to design this into your board you
could use a header and simply make the danghter board removable.



http://webpages.charter.net/jamie_5"