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https://designers-guide.org/forum/YaBB.pl Design >> Analog Design >> unused emitters https://designers-guide.org/forum/YaBB.pl?num=1201616006 Message started by MonteCarlo on Jan 29th, 2008, 6:13am |
Title: unused emitters Post by MonteCarlo on Jan 29th, 2008, 6:13am What should I do with the unsed emitters in a multi-emitter npn? Connect to base, collector, Vcc or Open Circuit? -Monte |
Title: Re: unused emitters Post by loose-electron on Feb 1st, 2008, 5:03pm As a general rule? Probably connect the emitter to the positive power rail, so that you keep the Vbe junction always turned off. Better yet, in a chip, do a layout that only has the emitters that you need. |
Title: Re: unused emitters Post by sheldon on Feb 2nd, 2008, 6:47pm Monte Carlo, What is the application, the power supply voltage of the design? How are you using the transistor, etc. Shorting the base and emitter should also be okay. The only concern about shorting the emitter to the positive power supply is that for high voltage applications, the B-E junction may breakdown and zener clamp the base to the power supply. So for 3V applications you should be okay, but for 15V applications, there could be issues. Best Regards, Sheldon |
Title: Re: unused emitters Post by loose-electron on Feb 4th, 2008, 12:42pm Sheldon - good point. Hopefully he has layout freedom to get rid of the unneeded emitters. -- Jerry |
Title: Re: unused emitters Post by thechopper on Feb 4th, 2008, 2:53pm Going back to Jerry´s suggestion, here´s one more thing to consider: Again depending on the application, you might not want to tie the emitter to the power supply in case leakage is a problem on the NPN´s base node: although the NPN is turned off it will leak thru BE junction if temp is high. Hope this helps Tosei |
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