I find this one rather confusing. The junction voltage is fixed by some relationships given in quantum physics. As far as I know (But what do I know?) there are not a variety of devices that successfully avoid the parameters that determine the junction potential restrictions. It would seem to me that any switching application that requires switching at a very low threshold, say in milivolts or microvolts, could be achieved by selecting the appropriate gain (Beta) for the device; Often a Darlington arrangement for small currents or a fet differential to a reference, or several other design approaches. The only caveat I see in the extremely low level operation is the noise, linearity and hysteresis over the range. These also can be addressed in the design error budget and essential performance spec. Why would someone be looking for a different junction voltage? If indeed that is what is being sought. I am at a loss to understand why this is a junction problem. ----- Original Message ----- From: "Vasile Surducan" To: "Microcontroller discussion list - Public." Sent: Saturday, May 13, 2006 3:21 PM Subject: Re: [EE]: NPN Transistor with low switch on voltage? > On 5/13/06, Spehro Pefhany wrote: >> At 12:38 PM 5/13/2006 +1200, you wrote: >> >> >> >Tell us how you are trying to do an unknown thing and we may not be >> >able to help. >> >Tell us what you want to achieve and we'll tell you how to achieve it. >> > RM >> >> I think what he wants to do is to take an audio signal (line level?) >> and modulate a fan controller based on the expected power dissipation >> in an audio amplifier, so that the fan tends to be quiet when the >> music is quiet, and loud when the music is blasting. > > > This simple trick and needs one: transistor, termistor (Kohm range), > resistor, capacitor, ventilator. > > Thermistor is sensing the radiator's temperature on which final > transistors are mounted. Transistor's load is a low current ventilator > connected from colector to Vcc, an RC from the transistor base to > ground and the thermistor from base to Vcc. Heating the termistor will > decrease his resistance so the transitor will be turned ON and the > ventilator will blow faster. It's a common scheme used in many > computer power supplies. > > Vasile > > > >> >> Something like a precision rectifier (couple of op-amps) into a PIC ADC >> and PWM output would fill the bill. The front end might not have to be >> than complex, of course. >> >> >Best regards, >> >> Spehro Pefhany --"it's the network..." "The Journey is the >> reward" >> speff@interlog.com Info for manufacturers: >> http://www.trexon.com >> Embedded software/hardware/analog Info for designers: >> http://www.speff.com >> ->>Test equipment, parts OLED displys >> http://search.ebay.com/_W0QQsassZspeff >> >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist