[sci.electronics] Transistor Selection

jwm712@unhd.unh.edu (Jonathan W Miner) (05/14/91)

This may be a FAQ, but I don't usally read this group:

  I need to switch a 12 volt / 1 Amp circuit using a 5 volt CMOS
  control.  What type of NPN transistor do I need?  I have
  used 2N3904's in past projects, but I know that they will
  not handle the current.  

Not being a regular reader of the group, Email is preferred.
I'll post a summary if enough people are interested.

Thanks in advance.
Jon.

-- 
Jonathan Miner        | I won't speak for UNH, and UNH does not 
jwm712@unhd.unh.edu   | speak for me, but they'll charge me anyway! 
(603)868-3416         | Hacking to graduate this May!
Moving soon to miner@mervax.sanders.com  (I think?!)

gibbonsj@iccgcc.decnet.ab.com (05/21/91)

In article <1991May14.003221.5725@unhd.unh.edu>, jwm712@unhd.unh.edu (Jonathan W Miner) writes:
>   I need to switch a 12 volt / 1 Amp circuit using a 5 volt CMOS
>   control.  What type of NPN transistor do I need?  I have

> Thanks in advance.
> Jon.

Don't use a bipolar transistor, use a MOSFET.  International Rectifier (IR) 
makes an IRF*** series that will do the job real nicely, and the gate drive just
looks like a 1000 pF cap (not too hard to drive with regular logic!).

If the load is inductive, be sure to damp the ringing with an RC snubber.
For example, the IRF531 has an Rds(on) resistance of 0.18 Ohms, and can handle 
60 volts Drain to source.   

Hope this helps!

-- 
  John Gibbons             N8OBJ                     Macedonia, Ohio

           "Welcome My Son, Welcome To The Machine" - Pink Floyd

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