LM339

Thread Starter

mbohuntr

Joined Apr 6, 2009
446
Another foolish question... I picked up a LM338 comparator to use in a recent expieriment, then realized the output was really a ground that could only sink 50mA. The light just came on, is this used to bias pnp transistors? What else can the 338 be used for? thanks, Mike
 

hgmjr

Joined Jan 28, 2005
9,027
Are you sure about the part number? A quick check of the datasheet indicates that the LM338 is a 3-terminal adjustable voltage regulator.

hgmjr
 

SgtWookie

Joined Jul 17, 2007
22,230
Comparators are very useful for "squaring up" signals that have slow transition times, particularly for inputs to logic devices.

Use a 1k to 1.2k pull-up resistor on the output, and supply a small amount of feedback via a large resistor to the non-inverting input to provide hysteresis. That won't give you much source/sink capability, but it's fine for logic levels.

If you needed more current sourced/sunk at the output, you could always add transistors or MOSFETs.
 

eblc1388

Joined Nov 28, 2008
1,542
Another foolish question... I picked up a LM338(LM339) comparator to use in a recent expieriment, then realized the output was really a ground that could only sink 50mA.
Read the LM339 datasheet carefully. It only show typical 16mA output current.

50mA shown in the datasheet is the input current.
 

Thread Starter

mbohuntr

Joined Apr 6, 2009
446
Thanks, looks like it will stay on the shelf till I find a good use for it... I'll have to see what transistors can be biased w/ <16mA.
 
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