MOSFET Usage
in [Design]
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From: Joe G (Home) on 23 May 2010 10:01 another MOSFET web site that might be useful. http://homepages.which.net/~paul.hills/SpeedControl/Mosfets.html
From: Ron M. on 24 May 2010 19:32 On May 22, 10:42 am, "Joe G \(Home\)" <jo...(a)optusnet.com.au> wrote: > "Ron M." <strmbr...(a)hotmail.com> wrote in message > > news:a67274a4-1270-45cf-8c90-4f139be8ad3c(a)y12g2000vbr.googlegroups.com... > > >I am in the process of designing a device that uses 30A MOSFET for the > > output. I need it to apply a 12 Vdc source to a switchable load on the > > ground side. Are there any major issues using a MOSFET in this way? > > What is the load type, inductive (motor etc) capacitive, resistive? > > What is the peak current on switch on? > > Have you done thermal calcuations of the MOSFET and heat sink? > > What is the operating temprature range? Do the thermal calcualtions meet > the MOSFET thermal requirements? > > What is the operating voltage? Is the max_Vds of the MOSEFT much greater > than the operating voltage. > > What is the Vgs_turn_voltage? Is it much greater than the MOSFET > Vgs_turn_on_threshold? > > If you answer these questions then you are well on your way to operating the > MOSFET correctly. > > PS... good clues on MOSFET operation may be obtained from here. > > http://www.btipnow.com/events/training.php > > Joe I knew this would go crazy if didn't spell things out. OK here we go. The MOSFET will be switching a 2 ohm (resistive) load for approx 100 - 200 ms. It will be controlled via 555 output. The MOSFET needs to have plus attached all the time and the load will be between the MOSFET and ground and will be several loads switched in one at a time. Basically this is the output for a sequencer that will be used to provide power to several different strings of devices (9 outputs in sequence by 20 sequences). The different sequences will be switched in manually using diode matrixing and siwtched grounds (relay). I know the MOSFET can handle the amount of current and power factors being used. Just wasn't sure if the plus could be connected to the MOSFET all the time and the load between the MOSFET and ground. Haven't used them much and wanted to save myself some grief during the design stages. They aren't that expensive $1.80 each but why blow em up if you don't gotta. THANKS for all the responses. Hopefully this will be enough for an informed opinion. THANKS folks.
From: neddie on 25 May 2010 07:56 On May 25, 1:32 am, "Ron M." <strmbr...(a)hotmail.com> wrote: > On May 22, 10:42 am, "Joe G \(Home\)" <jo...(a)optusnet.com.au> wrote: > > > > > "Ron M." <strmbr...(a)hotmail.com> wrote in message > > >news:a67274a4-1270-45cf-8c90-4f139be8ad3c(a)y12g2000vbr.googlegroups.com.... > > > >I am in the process of designing a device that uses 30A MOSFET for the > > > output. I need it to apply a 12 Vdc source to a switchable load on the > > > ground side. Are there any major issues using a MOSFET in this way? > > > What is the load type, inductive (motor etc) capacitive, resistive? > > > What is the peak current on switch on? > > > Have you done thermal calcuations of the MOSFET and heat sink? > > > What is the operating temprature range? Do the thermal calcualtions meet > > the MOSFET thermal requirements? > > > What is the operating voltage? Is the max_Vds of the MOSEFT much greater > > than the operating voltage. > > > What is the Vgs_turn_voltage? Is it much greater than the MOSFET > > Vgs_turn_on_threshold? > > > If you answer these questions then you are well on your way to operating the > > MOSFET correctly. > > > PS... good clues on MOSFET operation may be obtained from here. > > >http://www.btipnow.com/events/training.php > > > Joe > > I knew this would go crazy if didn't spell things out. OK here we go. > The MOSFET will be switching a 2 ohm (resistive) load for approx 100 - > 200 ms. It will be controlled via 555 output. The MOSFET needs to have > plus attached all the time and the load will be between the MOSFET and > ground and will be several loads switched in one at a time. Basically > this is the output for a sequencer that will be used to provide power > to several different strings of devices (9 outputs in sequence by 20 > sequences). The different sequences will be switched in manually using > diode matrixing and siwtched grounds (relay). I know the MOSFET can > handle the amount of current and power factors being used. Just wasn't > sure if the plus could be connected to the MOSFET all the time and the > load between the MOSFET and ground. Haven't used them much and wanted > to save myself some grief during the design stages. They aren't that > expensive $1.80 each but why blow em up if you don't gotta. THANKS for > all the responses. Hopefully this will be enough for an informed > opinion. THANKS folks. Do you want to use N-channel or P-channel mosfets. Using the latter would be easier for switching grounded loads.
From: neddie on 25 May 2010 09:40 On May 25, 1:56 pm, neddie <seegoo...(a)yahoo.com> wrote: > On May 25, 1:32 am, "Ron M." <strmbr...(a)hotmail.com> wrote: > > > > > On May 22, 10:42 am, "Joe G \(Home\)" <jo...(a)optusnet.com.au> wrote: > > > > "Ron M." <strmbr...(a)hotmail.com> wrote in message > > > >news:a67274a4-1270-45cf-8c90-4f139be8ad3c(a)y12g2000vbr.googlegroups.com.... > > > > >I am in the process of designing a device that uses 30A MOSFET for the > > > > output. I need it to apply a 12 Vdc source to a switchable load on the > > > > ground side. Are there any major issues using a MOSFET in this way? > > > > What is the load type, inductive (motor etc) capacitive, resistive? > > > > What is the peak current on switch on? > > > > Have you done thermal calcuations of the MOSFET and heat sink? > > > > What is the operating temprature range? Do the thermal calcualtions meet > > > the MOSFET thermal requirements? > > > > What is the operating voltage? Is the max_Vds of the MOSEFT much greater > > > than the operating voltage. > > > > What is the Vgs_turn_voltage? Is it much greater than the MOSFET > > > Vgs_turn_on_threshold? > > > > If you answer these questions then you are well on your way to operating the > > > MOSFET correctly. > > > > PS... good clues on MOSFET operation may be obtained from here. > > > >http://www.btipnow.com/events/training.php > > > > Joe > > > I knew this would go crazy if didn't spell things out. OK here we go. > > The MOSFET will be switching a 2 ohm (resistive) load for approx 100 - > > 200 ms. It will be controlled via 555 output. The MOSFET needs to have > > plus attached all the time and the load will be between the MOSFET and > > ground and will be several loads switched in one at a time. Basically > > this is the output for a sequencer that will be used to provide power > > to several different strings of devices (9 outputs in sequence by 20 > > sequences). The different sequences will be switched in manually using > > diode matrixing and siwtched grounds (relay). I know the MOSFET can > > handle the amount of current and power factors being used. Just wasn't > > sure if the plus could be connected to the MOSFET all the time and the > > load between the MOSFET and ground. Haven't used them much and wanted > > to save myself some grief during the design stages. They aren't that > > expensive $1.80 each but why blow em up if you don't gotta. THANKS for > > all the responses. Hopefully this will be enough for an informed > > opinion. THANKS folks. > > Do you want to use N-channel or P-channel mosfets. Using the latter > would be easier > for switching grounded loads. This is a simple way to do it. Used 555's to generate signals , but just to show the principle. If your load is purely resistive , ok. If inductive , use a diode across it . Use components (Fet) that came with LTSpice. There are probably better ones to use, that's up to you :0) Version 4 SHEET 1 1132 680 WIRE 848 -208 752 -208 WIRE 864 -208 848 -208 WIRE 1008 -208 864 -208 WIRE 864 -160 864 -208 WIRE 752 -96 752 -128 WIRE -80 -80 -544 -80 WIRE 32 -80 32 -96 WIRE -224 -32 -624 -32 WIRE 1008 -16 1008 -208 WIRE -80 0 -80 -80 WIRE 32 0 -16 0 WIRE 864 0 864 -80 WIRE 960 0 864 0 WIRE 400 80 400 64 WIRE 496 80 400 80 WIRE -192 96 -192 80 WIRE -96 96 -192 96 WIRE 112 96 64 96 WIRE 400 96 400 80 WIRE 400 96 336 96 WIRE -480 112 -528 112 WIRE -192 112 -192 96 WIRE -192 112 -256 112 WIRE 32 160 32 0 WIRE 112 160 32 160 WIRE 496 160 336 160 WIRE -624 176 -624 -32 WIRE -480 176 -624 176 WIRE -96 176 -256 176 WIRE 864 192 864 0 WIRE -96 208 -96 176 WIRE 112 224 48 224 WIRE 448 224 336 224 WIRE -544 240 -544 -80 WIRE -480 240 -544 240 WIRE -224 240 -224 -32 WIRE -224 240 -256 240 WIRE -144 240 -224 240 WIRE 688 240 656 240 WIRE 800 240 768 240 WIRE 448 272 448 224 WIRE 496 272 496 160 WIRE 496 272 448 272 WIRE -144 288 -144 240 WIRE -96 288 -144 288 WIRE 112 288 96 288 WIRE -480 304 -496 304 WIRE 1008 304 1008 80 WIRE 496 320 496 272 WIRE -624 352 -624 176 WIRE -624 512 -624 416 WIRE -368 512 -624 512 WIRE 496 512 496 384 WIRE 496 512 -368 512 WIRE 864 512 864 288 WIRE 864 512 496 512 WIRE 1008 512 1008 384 WIRE 1008 512 864 512 WIRE -368 544 -368 512 FLAG -528 112 0 FLAG -368 544 0 FLAG 752 -96 0 FLAG 848 -208 Vcc FLAG -496 304 Vcc FLAG -192 80 Vcc FLAG 656 240 Out FLAG 64 96 0 FLAG 96 288 Vcc FLAG 400 64 Vcc FLAG 48 224 Out FLAG 32 -96 Vcc SYMBOL Misc\\NE555 -368 208 R0 SYMATTR InstName U1 SYMBOL cap -640 352 R0 SYMATTR InstName C1 SYMATTR Value 4.7µ SYMBOL res -112 80 R0 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL res -112 192 R0 SYMATTR InstName R2 SYMATTR Value 200k SYMBOL voltage 752 -224 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL pmos 960 80 M180 SYMATTR InstName M1 SYMATTR Value FDS6375 SYMBOL res 848 -176 R0 SYMATTR InstName R3 SYMATTR Value 1k SYMBOL res 784 224 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R4 SYMATTR Value 1k SYMBOL res 992 288 R0 SYMATTR InstName LOAD SYMATTR Value 2 SYMBOL npn 800 192 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL Misc\\NE555 224 192 R0 SYMATTR InstName U2 SYMBOL cap 480 320 R0 SYMATTR InstName C2 SYMATTR Value 1.8µ SYMBOL res 480 64 R0 SYMATTR InstName R6 SYMATTR Value 100k SYMBOL res 16 -96 R0 SYMATTR InstName R7 SYMATTR Value 10k SYMBOL cap -16 -16 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C3 SYMATTR Value 100p TEXT -98 568 Left 0 !.tran 10
From: ian field on 25 May 2010 12:21
"neddie" <seegoon99(a)yahoo.com> wrote in message news:4a1cecae-c789-4601-8dd1-34b0daa6d242(a)y12g2000vbr.googlegroups.com... On May 25, 1:32 am, "Ron M." <strmbr...(a)hotmail.com> wrote: > On May 22, 10:42 am, "Joe G \(Home\)" <jo...(a)optusnet.com.au> wrote: > > > > > "Ron M." <strmbr...(a)hotmail.com> wrote in message > > >news:a67274a4-1270-45cf-8c90-4f139be8ad3c(a)y12g2000vbr.googlegroups.com... > > > >I am in the process of designing a device that uses 30A MOSFET for the > > > output. I need it to apply a 12 Vdc source to a switchable load on the > > > ground side. Are there any major issues using a MOSFET in this way? > > > What is the load type, inductive (motor etc) capacitive, resistive? > > > What is the peak current on switch on? > > > Have you done thermal calcuations of the MOSFET and heat sink? > > > What is the operating temprature range? Do the thermal calcualtions meet > > the MOSFET thermal requirements? > > > What is the operating voltage? Is the max_Vds of the MOSEFT much greater > > than the operating voltage. > > > What is the Vgs_turn_voltage? Is it much greater than the MOSFET > > Vgs_turn_on_threshold? > > > If you answer these questions then you are well on your way to operating > > the > > MOSFET correctly. > > > PS... good clues on MOSFET operation may be obtained from here. > > >http://www.btipnow.com/events/training.php > > > Joe > > I knew this would go crazy if didn't spell things out. OK here we go. > The MOSFET will be switching a 2 ohm (resistive) load for approx 100 - > 200 ms. It will be controlled via 555 output. The MOSFET needs to have > plus attached all the time and the load will be between the MOSFET and > ground and will be several loads switched in one at a time. Basically > this is the output for a sequencer that will be used to provide power > to several different strings of devices (9 outputs in sequence by 20 > sequences). The different sequences will be switched in manually using > diode matrixing and siwtched grounds (relay). I know the MOSFET can > handle the amount of current and power factors being used. Just wasn't > sure if the plus could be connected to the MOSFET all the time and the > load between the MOSFET and ground. Haven't used them much and wanted > to save myself some grief during the design stages. They aren't that > expensive $1.80 each but why blow em up if you don't gotta. THANKS for > all the responses. Hopefully this will be enough for an informed > opinion. THANKS folks. Do you want to use N-channel or P-channel mosfets. Using the latter would be easier for switching grounded loads. *************** If an old style iron cored transformer and rectifier is used as the power source its not too difficult to add a voltage doubling rectifier to provide an additional rail for n-channel gate drive. It is usually possible to do something similar with an SMPSU, but usually this involves opening and modifying an approved assembly - something not everyone's willing to do. |