On 3/20/2017 6:59 PM, Joerg wrote:> On 2017-03-19 21:34, rickman wrote: >> I was looking to order some low current MOSFETs and realized all the >> popular items had thresholds of 3 volts and higher. I would like to use >> something that turns on pretty well at 3 volts so it won't need a 5 volt >> PSU. Any suggestions? I'm looking for a TO-92 case preferably but >> surface mount will be ok too. >> >> I could have sworn some years ago I tracked down a number of low >> threshold voltage FETs. But maybe those devices operated under 5 volts >> rather than under 3.3 volts. >> > > Assuming you want to switch power to some circuit and thus need P-channel: > > http://www.diodes.com/assets/Datasheets/DMP2100U.pdf > > Key is that Rdson is guaranteed at your min drive voltage, not just in > the graphs but in the tables. > > N-channel example: > > http://www.diodes.com/assets/Datasheets/DMP2100U.pdf > > A beefier one: > > http://www.diodes.com/assets/Datasheets/ds31837.pdfThe DMP2100U is a P channel and I am looking for an N channel device. However, the DMN2075U is N channel and looks like a very good device for very low voltage controls. Actually, I might need the P channel device for something else later. Thanks. -- Rick C
Low Threshold MOSFET
Started by ●March 20, 2017
Reply by ●March 20, 20172017-03-20
Reply by ●March 21, 20172017-03-21
Shop for parts with Vds < 30V. That's the biggest determining factor in transconductance per area. I namedropped RUM001L02T2CL here the other day. It's also very tiny, good for saving PCB area. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com "rickman" <gnuarm@gmail.com> wrote in message news:oanlv1$af7$1@dont-email.me...>I was looking to order some low current MOSFETs and realized all the >popular items had thresholds of 3 volts and higher. I would like to use >something that turns on pretty well at 3 volts so it won't need a 5 volt >PSU. Any suggestions? I'm looking for a TO-92 case preferably but surface >mount will be ok too. > > I could have sworn some years ago I tracked down a number of low threshold > voltage FETs. But maybe those devices operated under 5 volts rather than > under 3.3 volts. > > -- > > Rick C
Reply by ●March 21, 20172017-03-21
On 2017-03-20 19:29, rickman wrote:> On 3/20/2017 6:59 PM, Joerg wrote: >> On 2017-03-19 21:34, rickman wrote: >>> I was looking to order some low current MOSFETs and realized all the >>> popular items had thresholds of 3 volts and higher. I would like to use >>> something that turns on pretty well at 3 volts so it won't need a 5 volt >>> PSU. Any suggestions? I'm looking for a TO-92 case preferably but >>> surface mount will be ok too. >>> >>> I could have sworn some years ago I tracked down a number of low >>> threshold voltage FETs. But maybe those devices operated under 5 volts >>> rather than under 3.3 volts. >>> >> >> Assuming you want to switch power to some circuit and thus need >> P-channel: >> >> http://www.diodes.com/assets/Datasheets/DMP2100U.pdf >> >> Key is that Rdson is guaranteed at your min drive voltage, not just in >> the graphs but in the tables. >> >> N-channel example: >> >> http://www.diodes.com/assets/Datasheets/DMP2100U.pdf >> >> A beefier one: >> >> http://www.diodes.com/assets/Datasheets/ds31837.pdf > > The DMP2100U is a P channel and I am looking for an N channel device. > However, the DMN2075U is N channel and looks like a very good device for > very low voltage controls. Actually, I might need the P channel device > for something else later. Thanks. >You are welcome. They also make duals in small SMT 6-pin packages if you are ever fighting real estate on a board. When it has to be rock-bottom in cost a BJT can be the better choice and those also come "pre-biased" where there is a series bases resistor inside its package and sometimes also a B-E resistor. Some folks call them "digital transistors". -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●March 21, 20172017-03-21
On 2017-03-20 18:42, rickman wrote:> On 3/20/2017 6:47 PM, Hul Tytus wrote: >> Fairchild (whoever now) has a nice n channel device speced, if I remember >> correctly, at 1 volt max turn on. It served as a voltage follower op amp >> with lots of offset. They came from Mouser. > > Any more info than that? Threshold voltage is not easy to search on > because everyone specs it at a different current. Also the threshold > voltage can be a *lot* lower than the fully on voltage which is the > important one. Or is that what you mean? Still, it takes a lot of data > sheet searching to find a part that is optimal for low voltage control > and that is why I asked here. I am hoping to benefit from other's > experience. >Don't go by any graphs. Those only represent typical values. The processes used for MOSFETs have huge tolerances in threshold voltage, easily +/-30%. The only values to go by are guaranteed max Rdson values for a stated gate drive voltage. Typically two to five different gate drive voltages are spec'd. Must be in the tables. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●March 21, 20172017-03-21
Try fdv301n. I'll verify that in the morning if I get to the office. Hul rickman <gnuarm@gmail.com> wrote:> On 3/20/2017 6:47 PM, Hul Tytus wrote: > > Fairchild (whoever now) has a nice n channel device speced, if I remember > > correctly, at 1 volt max turn on. It served as a voltage follower op amp > > with lots of offset. They came from Mouser.> Any more info than that? Threshold voltage is not easy to search on > because everyone specs it at a different current. Also the threshold > voltage can be a *lot* lower than the fully on voltage which is the > important one. Or is that what you mean? Still, it takes a lot of data > sheet searching to find a part that is optimal for low voltage control > and that is why I asked here. I am hoping to benefit from other's > experience.> --> Rick C
Reply by ●March 21, 20172017-03-21
On 3/21/2017 7:36 PM, Hul Tytus wrote:> Try fdv301n. I'll verify that in the morning if I get to the office.Good number. Thanks. -- Rick C
Reply by ●March 22, 20172017-03-22
On Sunday, March 19, 2017 at 9:34:31 PM UTC-7, rickman wrote:> I was looking to order some low current MOSFETs and realized all the > popular items had thresholds of 3 volts and higher. I would like to use > something that turns on pretty well at 3 volts so it won't need a 5 volt > PSU. Any suggestions? I'm looking for a TO-92 case preferably but > surface mount will be ok too. > > I could have sworn some years ago I tracked down a number of low > threshold voltage FETs. But maybe those devices operated under 5 volts > rather than under 3.3 volts. > > -- > > Rick CIf you want really low threshold devices Advanced Linear has some zero offset +/-1mV ones. http://www.aldinc.com/pdf/ALD110800.pdf kevin
Reply by ●March 22, 20172017-03-22
On 3/19/2017 11:34 PM, rickman wrote:> I was looking to order some low current MOSFETs and realized all the > popular items had thresholds of 3 volts and higher. I would like to use > something that turns on pretty well at 3 volts so it won't need a 5 volt > PSU. Any suggestions? I'm looking for a TO-92 case preferably but > surface mount will be ok too. > > I could have sworn some years ago I tracked down a number of low > threshold voltage FETs. But maybe those devices operated under 5 volts > rather than under 3.3 volts. >We have been very happy with the FDN337N.
Reply by ●March 22, 20172017-03-22
On 3/22/2017 10:36 AM, John S wrote:> On 3/19/2017 11:34 PM, rickman wrote: >> I was looking to order some low current MOSFETs and realized all the >> popular items had thresholds of 3 volts and higher. I would like to use >> something that turns on pretty well at 3 volts so it won't need a 5 volt >> PSU. Any suggestions? I'm looking for a TO-92 case preferably but >> surface mount will be ok too. >> >> I could have sworn some years ago I tracked down a number of low >> threshold voltage FETs. But maybe those devices operated under 5 volts >> rather than under 3.3 volts. >> > > We have been very happy with the FDN337N.I was checking this out and found the prices are >$0.20 even on ebay buying 50 or more. Then I checked aliexpress and found this one... https://www.aliexpress.com/item/Free-shipping-100pcs-lot-FDN337N-screen-337-SOT-23-new-original/32718408974.html?spm=2114.01010208.3.18.ju58Ca&ws_ab_test=searchweb0_0,searchweb201602_2_10065_10130_10068_433_434_10136_10137_10138_10060_10062_10141_10056_10055_10054_301_10059_201_10531_10099_10530_129_10103_10102_10096_10052_10053_10050_10107_10142_10051_10106_10143_10526_10529_10084_10083_10080_10082_10081_10110_10111_10112_10113_10114_10037_10078_10079_10077_10073_10070_10122_10123_10124,searchweb201603_13,afswitch_1,ppcSwitch_5,single_sort_0_default&btsid=bc963ea4-0cae-4be3-95ba-e5fa2d2485cc&algo_expid=5043bdd6-47a3-424c-a756-09e1cbb36cd7-2&algo_pvid=5043bdd6-47a3-424c-a756-09e1cbb36cd7 $2.80 for 100 with free shipping! I would say that have to be fakes, but this store has been online for 3 years with 100%. How can they do that? -- Rick C
Reply by ●March 22, 20172017-03-22
On 3/22/2017 1:03 PM, rickman wrote:> On 3/22/2017 10:36 AM, John S wrote: >> On 3/19/2017 11:34 PM, rickman wrote: >>> I was looking to order some low current MOSFETs and realized all the >>> popular items had thresholds of 3 volts and higher. I would like to use >>> something that turns on pretty well at 3 volts so it won't need a 5 volt >>> PSU. Any suggestions? I'm looking for a TO-92 case preferably but >>> surface mount will be ok too. >>> >>> I could have sworn some years ago I tracked down a number of low >>> threshold voltage FETs. But maybe those devices operated under 5 volts >>> rather than under 3.3 volts. >>> >> >> We have been very happy with the FDN337N. > > I was checking this out and found the prices are >$0.20 even on ebay > buying 50 or more. Then I checked aliexpress and found this one... > > https://www.aliexpress.com/item/Free-shipping-100pcs-lot-FDN337N-screen-337-SOT-23-new-original/32718408974.html?spm=2114.01010208.3.18.ju58Ca&ws_ab_test=searchweb0_0,searchweb201602_2_10065_10130_10068_433_434_10136_10137_10138_10060_10062_10141_10056_10055_10054_301_10059_201_10531_10099_10530_129_10103_10102_10096_10052_10053_10050_10107_10142_10051_10106_10143_10526_10529_10084_10083_10080_10082_10081_10110_10111_10112_10113_10114_10037_10078_10079_10077_10073_10070_10122_10123_10124,searchweb201603_13,afswitch_1,ppcSwitch_5,single_sort_0_default&btsid=bc963ea4-0cae-4be3-95ba-e5fa2d2485cc&algo_expid=5043bdd6-47a3-424c-a756-09e1cbb36cd7-2&algo_pvid=5043bdd6-47a3-424c-a756-09e1cbb36cd7 > > > $2.80 for 100 with free shipping! I would say that have to be fakes, > but this store has been online for 3 years with 100%. How can they do > that?Don't know. I just discovered that the FDN337N is unobtanium for the next couple of months or more. That prompted me to find a substitute which I have not yet singled out. We need something in the next week or two. Crap! Sorry about that.
