L339 Difference Comparator

Trevor Tomic

Other Parts Discussed in Thread: LM339, LP339, LMV339

Hi everyone,

I'm working on a project with a 24V digital signal which I'm using to trigger a camera on the falling edge. The problem I'm having is that the digital signal has too much noise to create a reliable trigger so I'd like to implement a difference comparator to clean it up and outuput a clean 24V digital signal since a few useconds won't make a difference in my image.

I think the L339 will do this task but I don't have much experience with electronics and wanted a second opinion before moving forward with it.

If this is the part I'm looking for a believe I'll need Vcc=26V to get Vo=24V is this correct? Also would I need any external resistors or electrical components?

Thanks in advance,

Trevor

over 11 years ago

0 Ron Michallick over 11 years ago

TI__Guru**** 152406 points

Trevor,

The LM339 is open collector. VOH is set by pull up resistor.

This schematic is non inverting.

0 Trevor Tomic over 11 years ago in reply to Ron Michallick

Prodigy 20 points

Hi Ron,

Thanks for the detailed schematic. For my application I really need a higher cutoff voltage for the falling edge, sorry should of given more details. Ideally the cutoff would be in the 20-23V range. I expect that to do this I'd need to decrease R4 and increase R5? Say use a value of R4=4.7k and R5=15K?

In my rush to move forward I ordered the LP339, from the specs it looks like they'll act in a similar way but if necessary I'll order the LM339. I know I'm a little green so I really appreciate the help. Also just out of curiosity what is the simulation software you're using?

Best Regards,

Trevor

0 Ron Michallick over 11 years ago in reply to Trevor Tomic

TI__Guru**** 152406 points

Trevor,

I used Ti-Tina which is free software. http://www.ti.com/tool/tina-ti

The LM339 wasn't in the library, so I cut and pasted LM339 p-spice code into the LMV339 model. I did this by right click component and select "enter macro".
TI models are here http://www.ti.com/adc/docs/midlevel.tsp?contentId=55102

The LP uses less power than LM but sacrifices some speed in the process.

LM339 noninv comp.TSC

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L339 Difference Comparator