Reply by September 4, 20172017-09-04
On Saturday, September 2, 2017 at 6:39:56 PM UTC-4, Tim Williams wrote:
> <dagmargoodboat@yahoo.com> wrote in message > news:cfa51960-d831-4b3d-9d84-7dcde9df7ee1@googlegroups.com... > > Oh dear, an octal is one gate shy. Scratch that. But you could use an > > octal, make two drivers with six gates, and the last driver with one > > external buffer e.g., > > https://www.seventransistorlabs.com/Images/BoostedLogicGateDrive.png > > Although it still has the problem of coming up one short, if your signal > isn't inverted. > > Tim
Yes, a complementary emitter follower works well, but Klaus said no discretes. If it were allowed, a NPN-PNP in one package and a resistor from base to emitter gets you six drivers per 'AC14. -+- | |/ .----| | |>. |\ | | >---| >o----+--R1--+--> |/ | | | |<' '----| |\ ' | === I think that's a John Larkin fave. Cheers, James Arthur
Reply by Tim Williams September 3, 20172017-09-03
"whit3rd" <whit3rd@gmail.com> wrote in message 
news:6e18a20b-4d4c-44e2-99ae-de061a835096@googlegroups.com...
> How about > > <http://rohmfs.rohm.com/en/products/databook/datasheet/discrete/transistor/digital/emg8t2r-e.pdf> > > (plus a pullup resistor).
Well. To be fair, he didn't say it couldn't be a class A driver. You'll actually burn more money on the 10 ohm power resistor, though. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by whit3rd September 3, 20172017-09-03
On Friday, September 1, 2017 at 3:10:26 PM UTC-7, Klaus Kragelund wrote:


> 74AC14, which is very cheap, has 24mA drive, ca. 0.65V, which translates to euquivalent RDSon to about 26 ohms
> So, anyone got partnumber on a about 10 ohm or better logic level IC, dirt cheap, preferable 2-3 or more parts in a package
How about <http://rohmfs.rohm.com/en/products/databook/datasheet/discrete/transistor/digital/emg8t2r-e.pdf> (plus a pullup resistor).
Reply by Klaus Kragelund September 3, 20172017-09-03
On Sunday, September 3, 2017 at 12:39:56 AM UTC+2, Tim Williams wrote:
> <dagmargoodboat@yahoo.com> wrote in message > news:cfa51960-d831-4b3d-9d84-7dcde9df7ee1@googlegroups.com... > > Oh dear, an octal is one gate shy. Scratch that. But you could use an > > octal, make two drivers with six gates, and the last driver with one > > external buffer e.g., > > https://www.seventransistorlabs.com/Images/BoostedLogicGateDrive.png > > Although it still has the problem of coming up one short, if your signal > isn't inverted. >
That could be done with one of this tripple inverter tiny logic thingies :-)
Reply by Klaus Kragelund September 3, 20172017-09-03
On Saturday, September 2, 2017 at 11:47:34 PM UTC+2, John Larkin wrote:
> On Fri, 1 Sep 2017 23:33:01 -0700 (PDT), Klaus Kragelund > <klauskvik@hotmail.com> wrote: > > >On Saturday, September 2, 2017 at 1:02:43 AM UTC+2, John Larkin wrote: > >> On Fri, 1 Sep 2017 15:10:18 -0700 (PDT), Klaus Kragelund > >> <klauskvik@hotmail.com> wrote: > >> > >> >Hi > >> > > >> >I am using the 74AC14 for driving a medium power MOSFET > >> > > >> >I need it dirt cheap, so no external small signal MOSFET to help to drive the power MOSFET possible > >> > > >> >74AC14, which is very cheap, has 24mA drive, ca. 0.65V, which translates to euquivalent RDSon to about 26 ohms > >> > > >> >http://www.mouser.com/ds/2/149/74ACT14-1006522.pdf > >> > > >> >I could parallel 2 of them, but since my input is slowly moving, that would be an questionable approach > >> > > >> >So, anyone got partnumber on a about 10 ohm or better logic level IC, dirt cheap, preferable 2-3 or more parts in a package > >> > > >> >Cheers > >> > > >> >Klaus > >> > >> How about an HCT or ACT hex something, one section driving the other > >> five in parallel? You've basically got that in the AC14. > >> > > > >I drive 3 FETs, so that would be one package per FET. I would like to drive them all from a single IC, 3 pcs is too expensive. > > > >> I like ON SEMI NL37WZ16US, at abs max Vcc, three sections in > >> parallel, insanely fast, 12 cents, but that needs CMOS level drive, > >> not HCT. > >> > > > >That is a good one, similar to the other ones I found, equivalent resistance of about 17 ohms, but about 3 times to high > > You must be driving giant fets. The NL37WZ16 rise time, unloaded, is > about 700 ps. Driving the just-right-size fet, you can switch 50 volts > at 1 amp in about a nanosecond. >
The problem is not driving them on, but making sure that when they are off, that they stay off. Say you have a half bridge configuration and the top FET has been on. It is turned off, and some ns later, the lowside FET is turned on. WHen the midpoint voltage ramps quickly to GND, then the source-gate capacitance of the high side FET is subjected to high dV/dt, and that current runs out of the gate driver for the highside FET. So if the high side FET driver has non-zere impedance, the gate voltage will rise during the midpoint travelling to GND and that is enough to turn on the high side FET which translates into cross conduction. BAD
> Of course, our products are lowish quantity, and parts cost doesn't > usually matter much. I sometimes use two or even three of the tiny > triples in parallel (like, 9 gates!) to drive a mosfet.
I don't have that luxury :-)
> > "Anything worth doing is worth overdoing." > > - Meat Loaf > > > > > >I have looked into analog switches, which comes down in the numbers needed, but then the manufacturer knows well that he can ask for a higher price :-( > > The USB switches are fairly cheap and just a few ohms. >
Will check them out Cheers Klaus
Reply by September 2, 20172017-09-02
On Sat, 2 Sep 2017 14:24:03 -0700 (PDT), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

>On Saturday, September 2, 2017 at 4:00:12 PM UTC+2, John S wrote: >> On 9/1/2017 5:10 PM, Klaus Kragelund wrote: >> > Hi >> > >> > I am using the 74AC14 for driving a medium power MOSFET >> > >> > I need it dirt cheap, so no external small signal MOSFET to help to drive the power MOSFET possible >> > >> > 74AC14, which is very cheap, has 24mA drive, ca. 0.65V, which translates to euquivalent RDSon to about 26 ohms >> > >> > http://www.mouser.com/ds/2/149/74ACT14-1006522.pdf >> > >> > I could parallel 2 of them, but since my input is slowly moving, that would be an questionable approach >> > >> > So, anyone got partnumber on a about 10 ohm or better logic level IC, dirt cheap, preferable 2-3 or more parts in a package >> > >> > Cheers >> > >> > Klaus >> > >> >> What is the part number of your medium power MOSFET? > >https://www.diodes.com/assets/Datasheets/DMC4047LSD.pdf
Nice part! I may have a use for that one.
Reply by Dimitrij Klingbeil September 2, 20172017-09-02
On 02.09.2017 00:10, Klaus Kragelund wrote:
> Hi > > I am using the 74AC14 for driving a medium power MOSFET > > I need it dirt cheap, so no external small signal MOSFET to help to > drive the power MOSFET possible > > 74AC14, which is very cheap, has 24mA drive, ca. 0.65V, which > translates to euquivalent RDSon to about 26 ohms > > http://www.mouser.com/ds/2/149/74ACT14-1006522.pdf > > I could parallel 2 of them, but since my input is slowly moving, that > would be an questionable approach > > So, anyone got partnumber on a about 10 ohm or better logic level IC, > dirt cheap, preferable 2-3 or more parts in a package > > Cheers > > Klaus
You could at least try a permanently-enabled NC7SZ125 TinyLogic 3-state line driver (or its TI equivalent SN74LVC1G125). The datasheet does not say much, but my experience with them so far is, that they are considerably "beefier" than other typical logic outputs. If accidentally driven against a 3.3V CPU or FPGA output pin, it would easily overdrive the CPU / FPGA pin strongly enough to land at a valid opposite logic level. The only indication that something is wrong apart from the other chip not being made to stand this for very long, was a small voltage offset from VCC (or from GND) on the offending signal, an offset small enough to be quite easily overlooked. The datasheet specifies 32 mA output at 4.5 V supply, but that's rated output current. Peak current into a dead short is rather around 150 mA (not that the chip would be expected to survive it very long either). Dimitrij
Reply by Tim Williams September 2, 20172017-09-02
<dagmargoodboat@yahoo.com> wrote in message 
news:cfa51960-d831-4b3d-9d84-7dcde9df7ee1@googlegroups.com...
> Oh dear, an octal is one gate shy. Scratch that. But you could use an > octal, make two drivers with six gates, and the last driver with one > external buffer e.g.,
https://www.seventransistorlabs.com/Images/BoostedLogicGateDrive.png Although it still has the problem of coming up one short, if your signal isn't inverted. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by John Larkin September 2, 20172017-09-02
On Sat, 2 Sep 2017 14:24:03 -0700 (PDT), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

>On Saturday, September 2, 2017 at 4:00:12 PM UTC+2, John S wrote: >> On 9/1/2017 5:10 PM, Klaus Kragelund wrote: >> > Hi >> > >> > I am using the 74AC14 for driving a medium power MOSFET >> > >> > I need it dirt cheap, so no external small signal MOSFET to help to drive the power MOSFET possible >> > >> > 74AC14, which is very cheap, has 24mA drive, ca. 0.65V, which translates to euquivalent RDSon to about 26 ohms >> > >> > http://www.mouser.com/ds/2/149/74ACT14-1006522.pdf >> > >> > I could parallel 2 of them, but since my input is slowly moving, that would be an questionable approach >> > >> > So, anyone got partnumber on a about 10 ohm or better logic level IC, dirt cheap, preferable 2-3 or more parts in a package >> > >> > Cheers >> > >> > Klaus >> > >> >> What is the part number of your medium power MOSFET? > >https://www.diodes.com/assets/Datasheets/DMC4047LSD.pdf
Yikes. What switching speed do you want? -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by John Larkin September 2, 20172017-09-02
On Fri, 1 Sep 2017 23:33:01 -0700 (PDT), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

>On Saturday, September 2, 2017 at 1:02:43 AM UTC+2, John Larkin wrote: >> On Fri, 1 Sep 2017 15:10:18 -0700 (PDT), Klaus Kragelund >> <klauskvik@hotmail.com> wrote: >> >> >Hi >> > >> >I am using the 74AC14 for driving a medium power MOSFET >> > >> >I need it dirt cheap, so no external small signal MOSFET to help to drive the power MOSFET possible >> > >> >74AC14, which is very cheap, has 24mA drive, ca. 0.65V, which translates to euquivalent RDSon to about 26 ohms >> > >> >http://www.mouser.com/ds/2/149/74ACT14-1006522.pdf >> > >> >I could parallel 2 of them, but since my input is slowly moving, that would be an questionable approach >> > >> >So, anyone got partnumber on a about 10 ohm or better logic level IC, dirt cheap, preferable 2-3 or more parts in a package >> > >> >Cheers >> > >> >Klaus >> >> How about an HCT or ACT hex something, one section driving the other >> five in parallel? You've basically got that in the AC14. >> > >I drive 3 FETs, so that would be one package per FET. I would like to drive them all from a single IC, 3 pcs is too expensive. > >> I like ON SEMI NL37WZ16US, at abs max Vcc, three sections in >> parallel, insanely fast, 12 cents, but that needs CMOS level drive, >> not HCT. >> > >That is a good one, similar to the other ones I found, equivalent resistance of about 17 ohms, but about 3 times to high
You must be driving giant fets. The NL37WZ16 rise time, unloaded, is about 700 ps. Driving the just-right-size fet, you can switch 50 volts at 1 amp in about a nanosecond. Of course, our products are lowish quantity, and parts cost doesn't usually matter much. I sometimes use two or even three of the tiny triples in parallel (like, 9 gates!) to drive a mosfet. "Anything worth doing is worth overdoing." - Meat Loaf
> >I have looked into analog switches, which comes down in the numbers needed, but then the manufacturer knows well that he can ask for a higher price :-(
The USB switches are fairly cheap and just a few ohms. -- John Larkin Highland Technology, Inc lunatic fringe electronics