** Try measuring some - as I suggested.
Data sheets are often great works of fiction.
** Not with a Vce of near zero. ** Huh ?** It would be better to use a Schottky diode instead.
........ Phil
small signal NPN transitor for muting microphone
Jan 22, 2006
24 Replies
Why not use a MOSFET? It will handle the small AC signals perfectly, provided you don't yell into the mic & cause the MOSFET's diode to turn on. Cheers, Ian Du Rieu The Leon Audio Company
"Ian Du Rieu"
** That darn body diode plus higher cost.** Junction fets are sometimes used ( ie J111, 112, 113 ) - but have on resistances 50 to 100 times greater than a small signal transistor.
........ Phil
[snip]
That is correct. The drop of a bipolar device, when acting as a switch, is a function of inverse beta, the higher the inverse beta the lower the drop.
When a transistor is inverted, then "inverse" beta is actually the value of the "forward" beta.
Clear as mud, but I hope it covered the ground ?:-)
...Jim Thompson
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
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It\'s what you learn, after you know it all, that counts.
When bipolar transistors are are saturated they exhibit an offset voltage. If the emitter and collector are reversed in your circuit, then when the bipolar is on it will show virtually no offset voltage, i.e. the voltage between the emitter and collector is nearly zero. If it were me, I would not do it this way. I would use a 2N7000 CMOS transistor which is similar to the
2N2222, except the input impedance of the 2N7000 is infinite. Next use a 1uF capacitor to couple the 2N7000 drain to the signal channel. This may prevent a click when the mute is engaged. If you do get a click, then I would go to the VACTEC LED/Photoresistor module and also use the 1uF capacitor. The VACTEC photoresistor may be turned on softly (slowly) and this will allow the cap to charge slowly, below the bandpass of the channel (Join the Discussion
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