LM393 dual comparator

Thread Starter

AymanKhuzundar

Joined Apr 2, 2017
60
Hello everybody , I'm new on this site and wish You to help me
I use the LM393 to run a PNP transistor and the transistor is connected to my load , but I've found some people using it to run a NPN transistor using a feedback resistor - I guess - from the non-inverting input to the output and another resistor from the Vcc to the output , my question is why they prefer to do this ? what's the difference between the two ways ? is it better than that I use ? what are the advantages for both - if there is a difference -
Thanks all .
 

MrChips

Joined Oct 2, 2009
22,472
There are circuit applications for PNP transistors and there are circuit applications for NPN transistors.
You need to know when to use a PNP transistor and when to use a NPN transistor.
Post the two circuits you have in mind then we will be able to provide you with advice.
 

Dodgydave

Joined Jun 22, 2012
9,837
The Lm393 has an Open Collector output, so it cannot supply a Positive output, so the resistor is there to switch on the transistor.
 

dl324

Joined Mar 30, 2015
12,211
Welcome to AAC!

Here's your post using paragraphs to make it more readable:
Hello everybody , I'm new on this site and wish You to help me

I use the LM393 to run a PNP transistor and the transistor is connected to my load , but I've found some people using it to run a NPN transistor using a feedback resistor - I guess - from the non-inverting input to the output and another resistor from the Vcc to the output ,

my question is why they prefer to do this ? what's the difference between the two ways ? is it better than that I use ? what are the advantages for both - if there is a difference -

Thanks all .
Don't guess; post schematics.

Comparators are usually used with no feedback. It depends on the nature of input signals.

Most are open collector, like the LM393, but some newer designs aren't.
 

Thread Starter

AymanKhuzundar

Joined Apr 2, 2017
60
There are circuit applications for PNP transistors and there are circuit applications for NPN transistors.
You need to know when to use a PNP transistor and when to use a NPN transistor.
Post the two circuits you have in mind then we will be able to provide you with advice.
The load is a relay , how can I know when to use the PNP and the NPN ?
 

Thread Starter

AymanKhuzundar

Joined Apr 2, 2017
60
Well I'm amazed that the University has not told you to read Datasheets!!!, if your output is to ground then use a PNP.
Don't Know why Your answers is like that !!
I say I read the datasheet and use the PNP , nut found some people use the NPN , the question is whyyy they use the NPN ??? what is the difference ??? Just like that !!
 

Dodgydave

Joined Jun 22, 2012
9,837
The Second method as you ask is for using a PNP transistor this is Normal, whereas the first method, uses R2 to turn on the transistor and R3 for Hysteresis.
 
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