[time-nuts] HP5328A LEDS driver transistor

Charles P. Steinmetz charles_steinmetz at lavabit.com
Sun Jan 22 15:25:45 EST 2012

Chris wrote:

>Motorola MPS-U51
>I look up the spec in the mps-u51 and see it is a to-220 like case and
>can handle 1W.

The Motorola "Uniwatt" case was not really comfortable dissipating 
one watt even in 25 degree free air (the book spec).  I used them and 
their NPN counterpart, the MPS-U01 in a number of designs in the 
early '70s because they were the fastest medium-power transistors 
available.  We always used them with board-mounted heatsinks (unlike 
the TO-220 case, which uses a lead frame and has sturdy leads, the 
Uniwatt has flimsy wire leads similar to a TO-5/TO-39 package).

Any switching transistor that will handle 1-2A and has an fT in the 
50 MHz range or better should work fine.  Note the EBC 
pinout.  Today, I might replace it with a TO-237 device like the 
2N6726/27/28/29/30 from Central Semi (same free-air power rating as 
U51, same pinout).  But note, same optimistic free-air power spec -- 
I'd use a clip-on heatsink if I couldn't leave my finger on it indefinitely.


These seem to be EOL at this time, but still 
available.  ZTX953/951/753/751 (Diodes, Inc.) and KSA928A (Fairchild) 
are TO-92 devices that also claim high dissipation.  Again, use a heatsink.

Best regards,


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