Post by thread:[EE]: Are there any small germanium transistors st

Hi, Does anyone knows about any small signal germanium transistors that are still in production ???!! I need slower vbe than silicon to use in a short circuit protection system. The 0.6 volts of silicon transistor makes me use a large wire wound resistor that could have it's value divided by 3 and would also get the dissipation much lower. For this application the leakage problems should not make any difference. It is either that or complex op-amps circuits and the thing has high side drivers wich make it harder to measure current. The project is very price sensitive so I am not able to use protected FET's. Best regards, Alexandre Guimaraes -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Alexandre Guimarães wrote: > Hi, > > Does anyone knows about any small signal germanium transistors that are > still in production ???!! I believe that the short answer is no. The long answer is that SiGe (silicon-germanium combinations) are one of the very latest things for transistors for extremely high frequencies (up in the microwave range). But they're not what you're looking for. Electronic Goldmine has some NOS (very old) germanium transistors for $1 each: http://sales.goldmine-elec.com/prodinfo.asp?prodid=3661 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

{Quote hidden}> -----Original Message----- > From: Alexandre Guimarães [SMTP:spam_OUTalexgTakeThisOuTMS.MICROLINK.COM.BR] > Sent: Tuesday, June 18, 2002 10:49 AM > To: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU > Subject: [EE]: Are there any small germanium transistors still being > manufactured ? I need lower vbe !! > > Hi, > > Does anyone knows about any small signal germanium transistors that > are > still in production ???!! > > I need slower vbe than silicon to use in a short circuit protection > system. The 0.6 volts of silicon transistor makes me use a large wire > wound > resistor that could have it's value divided by 3 and would also get the > dissipation much lower. For this application the leakage problems should > not > make any difference. It is either that or complex op-amps circuits and the > thing has high side drivers wich make it harder to measure current. The > project is very price sensitive so I am not able to use protected FET's. > > Best regards, > Alexandre Guimaraes > You don't need to use a germanium device to reduce the value of the sense resistor. Use a diode to provide one Vbe volt drop on the output of the sense resistor and reference the base of the transistor to a fraction of the voltage accross the diode. This gives the possibility of very fine current control and reduces the temperature sensitivity of the current limit (depending on the fraction of the diode drop you sense). HTH. Regards Mike Rsense ---+-----\/\/\/\/---+--------+------ | | _|_ \ e \ \ / >|__________> / -+- /| b \ | / c / | | | | | +--------+ | | | \ | / | \ | / ---+-------------------------+------ | -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

{Quote hidden}> -----Original Message----- > From: Alexandre Guimarães [SMTP:alexgKILLspamMS.MICROLINK.COM.BR] > Sent: Tuesday, June 18, 2002 10:49 AM > To: .....PICLISTKILLspam.....MITVMA.MIT.EDU > Subject: [EE]: Are there any small germanium transistors still being > manufactured ? I need lower vbe !! > > Hi, > > Does anyone knows about any small signal germanium transistors that > are > still in production ???!! > > I need slower vbe than silicon to use in a short circuit protection > system. The 0.6 volts of silicon transistor makes me use a large wire > wound > resistor that could have it's value divided by 3 and would also get the > dissipation much lower. For this application the leakage problems should > not > make any difference. It is either that or complex op-amps circuits and the > thing has high side drivers wich make it harder to measure current. The > project is very price sensitive so I am not able to use protected FET's. > > Best regards, > Alexandre Guimaraes > Oops, I saw my stupid mistake just as I hit the send button! The collector would obviously go to whatever you are using to control voltage. Mike Rsense ---+-----\/\/\/\/---+--------+------ | | _|_ \ e \ \ / >|__________> / -+- /| b \ | / c / | | | | | +--------+ | | | \ v To current limit / \ / -----------------------------+------ | -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

At 06:49 AM 6/18/02 -0300, =?Windows-1252?Q?Alexandre_Guimar=E3es?= wrote: >Hi, > > Does anyone knows about any small signal germanium transistors that are >still in production ???!! > > I need slower vbe than silicon to use in a short circuit protection >system. The 0.6 volts of silicon transistor makes me use a large wire wound >resistor that could have it's value divided by 3 and would also get the >dissipation much lower. You can bias the base of the transistor so that it is not quite turned on. There are a couple of ways of doing this - how temperature stable does this whole thing need to be? The easiest way should just involve adding a single resistor. You probably have the base connected to your current sense resistor via a 1K or so protection resistor. Just add another resistor to the base that pulls the base towards conduction by 0.4V or so. The words sound confusing but it is very simple. It would be easier if you could describe your circuit. Or even better - draw your circuit in ASCII and post it. dwayne -- Dwayne Reid <EraseMEdwaynerspam_OUTTakeThisOuTplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 18 years of Engineering Innovation (1984 - 2002) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

You MAY be able to current sense at lower voltage drops using a long tailed pair using only two (or possibly three) transistors. Also something like an LM358 (dual opamp) or LM339 (quad comparator) is quite cheap - probably around $US0.20 in volume, maybe less.) Having a transistor partially turned on with external bias would also allow lower voltage drop across the sense resistor but complicates the circuit somewhat. Russell McMahon {Original Message removed}

Hi, Russel > You MAY be able to current sense at lower voltage drops using a long tailed > pair using only two (or possibly three) transistors. I am not quite sure that I could trust the match between the transistor to form a differential amplifier and get good results. It might be worth a try together with a "current mirror" circuit. A little more complex but might work. > Also something like an LM358 (dual opamp) or LM339 (quad comparator) is > quite cheap - probably around $US0.20 in volume, maybe less.) I have some problems with that option. The environment I will be working with has very noisy supply and voltage can go easily up to 80v ! I would have to power the opamp from a "shunt" power supply referenced to the positive rail because I have to use high side driver transistor and have not control on ground return ! Cheap op-amps do not like to work too close to the supply rails. Simple op-amps would be too much trouble in my opinion. > Having a transistor partially turned on with external bias would also allow > lower voltage drop across the sense resistor but complicates the circuit > somewhat. That is exactly what I am trying to accomplish right now. It should work but I am still trying to sort out some problems. I decided to use it using the RDS-ON off the FET together with the shunt resistor and there are some nasty problems when the FET is off or there is no load. As a good side effect I should be able to show when there is a short circuit or detect an open load condition. I should have it working by the end of next week and I will get the results back here. It is the least complicated solution, even with the added parts to bias the transistor. Best regards, Alexandre Guimaraes -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

> > You MAY be able to current sense at lower voltage drops using > a long tailed > > pair using only two (or possibly three) transistors. > > I am not quite sure that I could trust the match between the > transistor to form a differential amplifier and get good results How about a supermatch pair, eg LM394 ? http://www.national.com/pf/LM/LM394.html -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Hi, > > > You MAY be able to current sense at lower voltage drops using > > a long tailed > > > pair using only two (or possibly three) transistors. > > > > I am not quite sure that I could trust the match between the > > transistor to form a differential amplifier and get good results > > How about a supermatch pair, eg LM394 ? > > http://www.national.com/pf/LM/LM394.html Those are very expensive parts. It would be cheaper to buy a ready made current sensor chip ! Best regards, Alexandre Guimaraes -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body