Switch and fight (leakage)?
in [Design]
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From: John Larkin on 17 Apr 2010 15:45 On Sat, 17 Apr 2010 06:51:25 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"Jasen Betts" <jasen(a)xnet.co.nz> wrote in message >news:hqbqef$f4l$3(a)reversiblemaps.ath.cx... >> however photdiodes packed in black plastic are packaged >> in plastic that is transparent in the infrared, black >> in the visible wavelengths cuts down on interferance >> from fluorescent lights etc... > >I tested one of those with a red superbright. Just enough attenuation that >I got a useful signal with the LED positioned directly in front of the >sensor (CTR on the order of 0.01%). > >Tim Interesting. We *need* an optocoupler with a CTR of 0.01%. The current plan is to put the LED in a cavity in an aluminum block, with the PD in the other side, and use a setscrew in the middle that can, fully scrunched down, block all the light between. John
From: Artemus on 17 Apr 2010 16:57 "Phil Hobbs" <pcdhSpamMeSenseless(a)electrooptical.net> wrote in message news:4BC9CE8B.1060401(a)electrooptical.net... > > The old plastic transistors that were photosensitive were > phenolic-encapsulated, iirc. Metal can transistors detect light that > gets in through the green frit seals--it usually takes direct sunlight > before that's a problem, but it can be very puzzling! > You got that right. Ages ago I was a test development engineer for an analog semi company. One day I get a call from product engineering saying the equipment I designed is screwed up and failing all the opamps in TO99 packages for excess Ib. I took my golden units out to production and had them tested. The data matched my old data quite nicely. After much head scratching it was determined that the package vendor had switched the glass on the frit seals and light was entering and reflecting off the lid of the can. It was puzzling but fun too as it wasn't some old problem again for the Nth time. Art
From: Fred Bartoli on 17 Apr 2010 17:36 Phil Hobbs a �crit : > On 4/17/2010 4:10 AM, Jasen Betts wrote: >> On 2010-04-16, Jim >> Thompson<To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >>> On Fri, 16 Apr 2010 01:27:15 -0700, Robert Baer >>> <robertbaer(a)localnet.com> wrote: >> >>> Even those diodes (and transistors) packaged in black plastic exhibit >>> photo effects. >>> >>> TI used to have a whole series of IR diodes (for TV remote links) that >>> had no window. >> >> I've seen some like that, a bare silicon wafer. >> >> however photdiodes packed in black plastic are packaged >> in plastic that is transparent in the infrared, black >> in the visible wavelengths cuts down on interferance >> from fluorescent lights etc... >> >>> And, John, they don't "leak when light hits them"... what a dummy :-) >> >> >> --- news://freenews.netfront.net/ - complaints: news(a)netfront.net --- > > The old plastic transistors that were photosensitive were > phenolic-encapsulated, iirc. Metal can transistors detect light that > gets in through the green frit seals--it usually takes direct sunlight > before that's a problem, but it can be very puzzling! > Yup. I had exactly this happening with the input Jfets of my 200pV/rtHz preamplifier built a few years ago. Measurements gave way too much of 1/f noise. A cloud passes => pb solved. Of course it was hard to sell the cloud with the preamp... -- Thanks, Fred.
From: Joerg on 17 Apr 2010 18:38
Fred Bartoli wrote: > Phil Hobbs a �crit : >> On 4/17/2010 4:10 AM, Jasen Betts wrote: >>> On 2010-04-16, Jim >>> Thompson<To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >>>> On Fri, 16 Apr 2010 01:27:15 -0700, Robert Baer >>>> <robertbaer(a)localnet.com> wrote: >>> >>>> Even those diodes (and transistors) packaged in black plastic exhibit >>>> photo effects. >>>> >>>> TI used to have a whole series of IR diodes (for TV remote links) that >>>> had no window. >>> >>> I've seen some like that, a bare silicon wafer. >>> >>> however photdiodes packed in black plastic are packaged >>> in plastic that is transparent in the infrared, black >>> in the visible wavelengths cuts down on interferance >>> from fluorescent lights etc... >>> >>>> And, John, they don't "leak when light hits them"... what a dummy :-) >>> >>> >>> --- news://freenews.netfront.net/ - complaints: news(a)netfront.net --- >> >> The old plastic transistors that were photosensitive were >> phenolic-encapsulated, iirc. Metal can transistors detect light that >> gets in through the green frit seals--it usually takes direct sunlight >> before that's a problem, but it can be very puzzling! >> > > Yup. I had exactly this happening with the input Jfets of my 200pV/rtHz > preamplifier built a few years ago. > Measurements gave way too much of 1/f noise. A cloud passes => pb solved. > Of course it was hard to sell the cloud with the preamp... > Don't you guys have a longer term cloud these days? I mean the one from way up north, not the financial one from the south :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |