A Jfet to use for switching?
in [Design]
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From: Bitrex on 10 Feb 2010 23:36 Joerg wrote: > Bitrex wrote: >> John Larkin wrote: >>> On Tue, 09 Feb 2010 19:46:38 -0500, Bitrex >>> <bitrex(a)de.lete.earthlink.net> wrote: >>> >>>> Can anyone recommend an N channel TO-92 JFET that would be good for >>>> signal switching in a battery powered application? The on >>>> resistance isn't really critical, but the supply voltage and the >>>> signal amplitude require that the pinchoff voltage always be less >>>> than -2 volts or so. >>> >>> No chance of using an integrated CMOS analog switch? >>> >>> John >>> >> >> I only need one switch, and as a hobbyist doing a prototype on >> breadboard I was hoping to use through-hole components. ... > > > You really should try to overcome that limitation. If you shun SOT23 > devices you are going to be missing out on a world of new and wonderful > devices. BF862 and such. > > http://www.nxp.com/documents/data_sheet/BF862.pdf > > [...] > Agreed. Small PCBs are inexpensive enough through services like BatchPCB that it seems silly to spend time constructing some circuits on protoboard. For more experimental designs I have been able to find some custom designed blob-boards that support both through-hole and surface mount components.
From: Bitrex on 10 Feb 2010 23:36 Thanks gentlemen, for all your helpful advice!
From: Paul E. Schoen on 11 Feb 2010 21:57 "Joerg" <invalid(a)invalid.invalid> wrote in message news:7tgb0lFqjjU5(a)mid.individual.net... > Bitrex wrote: >> >> I only need one switch, and as a hobbyist doing a prototype on >> breadboard I was hoping to use through-hole components. ... > > > You really should try to overcome that limitation. If you shun SOT23 > devices you are going to be missing out on a world of new and wonderful > devices. BF862 and such. > > http://www.nxp.com/documents/data_sheet/BF862.pdf Until recently I used all THT components, even for production. But I found that, with a bit of practice and good magnifying goggles, good lighting, and a decent soldering iron, I was able to handle SMT components quite easily. SOT23 has 1.9 mm spacing, which is no sweat. SOIC components have 1.28 mm and are easy to work with. My greatest challenges have been PLCC devices with 0.95 mm and TSSOP with 0.65 mm pitch. That was pretty much the limit of what I could do with the tools I had. I had considered a 0.5 mm QFN-28 part but decided it was beyond what I could do by hand. I find that I don't do a whole lot of breadboarding anymore. Most of my projects will eventually be used for at least small scale production, and I usually make the first prototype PCB with several alternative parts and room for extra components and thru-hole test points where I can hang other parts if required. I have some adapters for SMT that have pads brought out for breadboarding but I've seldom used them. The technique I use for SMT soldering is to coat the pads with liquid flux. Then I set the SMT device in place, and the flux is usually thick enough to make it stick. Then I hold the part in place with a pointed probe or tip of sharp tweezers, and touch one lead with a slim tip soldering iron with a small amount of solder on it. When it melts, I remove heat, and then solder an opposite leg. With the right temperature iron, I find that you can solder the remaining legs easily, using minimal extra solder, as the board often has almost enough solder already plated on the pads. Paul
From: Joerg on 14 Feb 2010 16:50 Paul E. Schoen wrote: > "Joerg" <invalid(a)invalid.invalid> wrote in message > news:7tgb0lFqjjU5(a)mid.individual.net... >> Bitrex wrote: >>> I only need one switch, and as a hobbyist doing a prototype on >>> breadboard I was hoping to use through-hole components. ... >> >> You really should try to overcome that limitation. If you shun SOT23 >> devices you are going to be missing out on a world of new and wonderful >> devices. BF862 and such. >> >> http://www.nxp.com/documents/data_sheet/BF862.pdf > > Until recently I used all THT components, even for production. But I found > that, with a bit of practice and good magnifying goggles, good lighting, > and a decent soldering iron, I was able to handle SMT components quite > easily. SOT23 has 1.9 mm spacing, which is no sweat. SOIC components have > 1.28 mm and are easy to work with. My greatest challenges have been PLCC > devices with 0.95 mm and TSSOP with 0.65 mm pitch. That was pretty much the > limit of what I could do with the tools I had. I had considered a 0.5 mm > QFN-28 part but decided it was beyond what I could do by hand. > > I find that I don't do a whole lot of breadboarding anymore. Most of my > projects will eventually be used for at least small scale production, and I > usually make the first prototype PCB with several alternative parts and > room for extra components and thru-hole test points where I can hang other > parts if required. I have some adapters for SMT that have pads brought out > for breadboarding but I've seldom used them. > With one clever cut you can place SOT23 parts onto almost any Vector board. Onto the ones with square pads even without cuts if you accept the odd looks of parts placed at 45 degree angle. > The technique I use for SMT soldering is to coat the pads with liquid flux. > Then I set the SMT device in place, and the flux is usually thick enough to > make it stick. Then I hold the part in place with a pointed probe or tip of > sharp tweezers, and touch one lead with a slim tip soldering iron with a > small amount of solder on it. When it melts, I remove heat, and then solder > an opposite leg. With the right temperature iron, I find that you can > solder the remaining legs easily, using minimal extra solder, as the board > often has almost enough solder already plated on the pads. > I use the thinnest Kester No-Clean there is, 15mils. Leaded, of course. Gets the job done and I don't have to clean up the flux. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: MooseFET on 14 Feb 2010 21:02 On Feb 14, 1:50 pm, Joerg <inva...(a)invalid.invalid> wrote: > Paul E. Schoen wrote: > > "Joerg" <inva...(a)invalid.invalid> wrote in message > >news:7tgb0lFqjjU5(a)mid.individual.net... > >> Bitrex wrote: > >>> I only need one switch, and as a hobbyist doing a prototype on > >>> breadboard I was hoping to use through-hole components. ... > > >> You really should try to overcome that limitation. If you shun SOT23 > >> devices you are going to be missing out on a world of new and wonderful > >> devices. BF862 and such. > > >>http://www.nxp.com/documents/data_sheet/BF862.pdf > > > Until recently I used all THT components, even for production. But I found > > that, with a bit of practice and good magnifying goggles, good lighting, > > and a decent soldering iron, I was able to handle SMT components quite > > easily. SOT23 has 1.9 mm spacing, which is no sweat. SOIC components have > > 1.28 mm and are easy to work with. My greatest challenges have been PLCC > > devices with 0.95 mm and TSSOP with 0.65 mm pitch. That was pretty much the > > limit of what I could do with the tools I had. I had considered a 0.5 mm > > QFN-28 part but decided it was beyond what I could do by hand. > > > I find that I don't do a whole lot of breadboarding anymore. Most of my > > projects will eventually be used for at least small scale production, and I > > usually make the first prototype PCB with several alternative parts and > > room for extra components and thru-hole test points where I can hang other > > parts if required. I have some adapters for SMT that have pads brought out > > for breadboarding but I've seldom used them. > > With one clever cut you can place SOT23 parts onto almost any Vector > board. Onto the ones with square pads even without cuts if you accept > the odd looks of parts placed at 45 degree angle. > > > The technique I use for SMT soldering is to coat the pads with liquid flux. > > Then I set the SMT device in place, and the flux is usually thick enough to > > make it stick. Then I hold the part in place with a pointed probe or tip of > > sharp tweezers, and touch one lead with a slim tip soldering iron with a > > small amount of solder on it. When it melts, I remove heat, and then solder > > an opposite leg. With the right temperature iron, I find that you can > > solder the remaining legs easily, using minimal extra solder, as the board > > often has almost enough solder already plated on the pads. > > I use the thinnest Kester No-Clean there is, 15mils. Leaded, of course. > Gets the job done and I don't have to clean up the flux. Never use "no clean" flux. The stuff is just nasty because it only takes a little exposure to any hydrocarbon to make the ions get loose and start causing trouble. > > -- > Regards, Joerg > > http://www.analogconsultants.com/ > > "gmail" domain blocked because of excessive spam. > Use another domain or send PM.
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