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MonteCarlo New Member Offline Posts: 8	unused emitters Jan 29^th, 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
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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: unused emitters Reply #1 - Feb 1^st, 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.
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sheldon

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Re: unused emitters
Reply #2 - Feb 2^nd, 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

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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: unused emitters Reply #3 - Feb 4^th, 2008, 12:42pm Sheldon - good point. Hopefully he has layout freedom to get rid of the unneeded emitters. -- Jerry
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HdrChopper Community Fellow Offline Posts: 493	Re: unused emitters Reply #4 - Feb 4^th, 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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