[time-nuts] HP5328A LEDS driver transistor

Charles P. Steinmetz charles_steinmetz at lavabit.com
Mon Jan 23 17:27:32 EST 2012

Stan wrote:

>The 5328A manual I have shows a 3.5 V supply (looks like it is used just
>for the display).  But with a bit lower Vce sat drops, I'd guess you 
>get around
>1 V across the 10 ohm segment resistors.  Or only about 900 mA when all
>9 segments are on (but at a low duty cycle).  Did HP also use a 5 V version
>of the driver in some 5328A counters?

Interesting.  I have 3 different sets of schematics for the 
5328A.  The most legible of these (thus the one I consult first) 
shows a 5 V supply for the display.  The other two show 3.5 V, as 
yours does.  I cannot recall ever measuring the display supply 
voltage in a 5328.

Even with 900 mA per digit, I'd want a transistor with >/=2 A maximum 
collector current for the digit drivers -- so I still think the 
ZTX949 may be the best readily-available choice.

Best regards,


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