>-----Original Message-----
>From: Olin Lathrop [mailto:olin_piclist@EMBEDINC.COM]
>Sent: 20 January 2004 12:42
>To: PICLIST@MITVMA.MIT.EDU
>Subject: Re: [EE:] IR modulator schematic?
>
>
>Jinx wrote:
>> I recommend Zetex transistors for the LED switching. They're heaps
>> better than common junk-box transistors (eg 2N2222, BC548, BC337 etc)
>
>Why?  An IR led is typically driven with 50-100mA.  I don't
>see why that should be a problem for a junkbox transistor,
>like the 2N4401 I use for such purposes.

They are better in a couple of respects:  They have a surprisingly high gain
at high collector currents, which means you aren't wasted power driving the
base hard.  They also have a very low Vcesat compared to average signal
transistors, which may be important if you have a remote running from e.g.
3volts.  They also come in the tiny (for a leaded component) E-line package
which may be good news if space is tight.

The downside (as always) is cost and to a lesser extent availability.

Regards

Mike




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